Activiti User Guide

The snippet below adds 2 listeners to a process-definition. The first listener will receive events of any type, with a listener implementation based on a fully-qualified class name. The second listener is only notified when a job is successfully executed or when it failed, using a listener that has been defined in the beans property of the process engine configuration.

For events related to entities, it’s also possible to add listeners to a process-definition that get only notified when entity-events occur for a certain entity type. The snippet below shows how this can be achieved. It can be used along for ALL entity-events (first example) or for specific event types only (second example).

Supported values for the entityType are: attachment, comment, execution, identity-link, job, process-instance, process-definition, task.

[EXPERIMENTAL]

Another way of handling events being dispatched is to throw a BPMN event. Please bear in mind that it only makes sense to throw BPMN-events with certain kinds of Activiti event types. For example, throwing a BPMN event when the process-instance is deleted will result in an error. The snippet below shows how to throw a signal inside process-instance, throw a signal to an external process (global), throw a message-event inside the process-instance and throw an error-event inside the process-instance. Instead of using the class or delegateExpression, the attribute throwEvent is used, along with an additional attribute, specific to the type of event being thrown.

If additional logic is needed to decide whether or not to throw the BPMN-event, it’s possible to extend the listener-classes provided by Activiti. By overriding the isValidEvent(ActivitiEvent event) in your subclass, the BPMN-event throwing can be prevented. The classes involved are +org.activiti.engine.test.api.event.SignalThrowingEventListenerTest, org.activiti.engine.impl.bpmn.helper.MessageThrowingEventListener and org.activiti.engine.impl.bpmn.helper.ErrorThrowingEventListener.

A signal can either be thrown by a process instance using a BPMN construct or programmatically using java API. The following methods on the org.activiti.engine.RuntimeService can be used to throw a signal programmatically:

The difference between signalEventReceived(String signalName); and signalEventReceived(String signalName, String executionId); is that the first method throws the signal globally to all subscribed handlers (broadcast semantics) and the second method delivers the signal to a specific execution only.

A signal event can be caught by an intermediate catch signal event or a signal boundary event.

It is possible to query for all executions which have subscribed to a specific signal event:

We could then use the signalEventReceived(String signalName, String executionId) method to deliver the signal to these executions.

By default, signals are broadcast process engine wide. This means that you can throw a signal event in a process instance, and other process instances with different process definitions can react on the occurrence of this event.

However, sometimes it is wanted to react to a signal event only within the same process instance. A use case for example is a synchronization mechanism in the process instance, if two or more activities are mutually exclusive.

To restrict the scope of the signal event, add the (non-BPMN 2.0 standard!) scope attribute to the signal event definition:

The default value for this is attribute is "global".

The following is an example of two separate processes communicating using signals. The first process is started if an insurance policy is updated or changed. After the changes have been reviewed by a human participant, a signal event is thrown, signaling that a policy has changed:

This event can now be caught by all process instances which are interested. The following is an example of a process subscribing to the event.

Note: it is important to understand that a signal event is broadcast to all active handlers. This means in the case of the example given above, that all instances of the process catching the signal would receive the event. In this case this is what we want. However, there are also situations where the broadcast behavior is unintended. Consider the following process:

The pattern described in the process above is not supported by Activiti. The idea is that the error thrown while performing the "do something" task is caught by the boundary error event and would be propagated to the parallel path of execution using the signal throw event and then interrupt the "do something in parallel" task. So far Activiti would perform as expected. The signal would be propagated to the catching boundary event and interrupt the task. However, due to the broadcast semantics of the signal, it would also be propagated to all other process instances which have subscribed to the signal event. In this case, this might not be what we want.

Note: the signal event does not perform any kind of correlation to a specific process instance. On the contrary, it is broadcast to all process instances. If you need to deliver a signal to a specific process instance only, perform correlation manually and use signalEventReceived(String signalName, String executionId) and the appropriate query mechanisms.

As an embeddable process engine, Activiti is not concerned with actually receiving a message. This would be environment dependent and entail platform-specific activities like connecting to a JMS (Java Messaging Service) Queue/Topic or processing a Webservice or REST request. The reception of messages is therefore something you have to implement as part of the application or infrastructure into which the process engine is embedded.

After you have received a message inside your application, you must decide what to do with it. If the message should trigger the start of a new process instance, choose between the following methods offered by the runtime service:

These methods allow starting a process instance using the referenced message.

If the message needs to be received by an existing process instance, you first have to correlate the message to a specific process instance (see next section) and then trigger the continuation of the waiting execution. The runtime service offers the following methods for triggering an execution based on a message event subscription:

Since there can only be one process definition for a specific message subscription, the query always returns zero or one results. If a process definition is updated, only the newest version of the process definition has a subscription to the message event.

Such queries are called correlation queries and usually require knowledge about the processes (in this case that there will be at most one process instance for a given orderId).

The following is an example of a process which can be started using two different messages:

This is useful if the process needs alternative ways to react to different start events but eventually continues in a uniform way.

A none start event technically means that the trigger for starting the process instance is unspecified. This means that the engine cannot anticipate when the process instance must be started. The none start event is used when the process instance is started through the API by calling one of the startProcessInstanceByXXX methods.

Note: a subprocess always has a none start event.

A none start event is visualized as a circle with no inner icon (i.e. no trigger type).

The XML representation of a none start event is the normal start event declaration, without any sub-element (other start event types all have a sub-element declaring the type).

formKey: references to a form template that users have to fill in when starting a new process instance. More information can be found in the forms section Example:

A timer start event is used to create process instance at given time. It can be used both for processes which should start only once and for processes that should start in specific time intervals.

Note: a subprocess cannot have a timer start event.

Note: a start timer event is scheduled as soon as process is deployed. There is no need to call startProcessInstanceByXXX, although calling start process methods is not restricted and will cause one more starting of the process at the time of startProcessInstanceByXXX Invocation.

Note: when a new version of a process with a start timer event is deployed, the job corresponding with the previous timer will be removed. The reasoning is that normally it is not wanted to keep automatically starting new process instances of this old version of the process.

A timer start event is visualized as a circle with clock inner icon.

The XML representation of a timer start event is the normal start event declaration, with timer definition sub-element. Please refer to timer definitions for configuration details.

Example: process will start 4 times, in 5 minute intervals, starting on 11th march 2011, 12:13

Example: process will start once, on selected date

A message start event can be used to start a process instance using a named message. This effectively allows us to select the right start event from a set of alternative start events using the message name.

When deploying a process definition with one or more message start events, the following considerations apply:

When starting a process instance, a message start event can be triggered using the following methods on the RuntimeService:

The messageName is the name given in the name attribute of the message element referenced by the messageRef attribute of the messageEventDefinition. The following considerations apply when starting a process instance:

A message start event is visualized as a circle with a message event symbol. The symbol is unfilled, to visualize the catching (receiving) behavior.

The XML representation of a message start event is the normal start event declaration with a messageEventDefinition child-element:

A signal start event can be used to start a process instance using a named signal. The signal can be fired from within a process instance using the intermediary signal throw event or through the API (runtimeService.signalEventReceivedXXX methods). In both cases, all process definitions that have a signal start event with the same name will be started.

Note that in both cases, it is also possible to choose between a synchronous and asynchronous starting of the process instances.

The signalName that must be passed in the API is the name given in the name attribute of the signal element referenced by the signalRef attribute of the signalEventDefinition.

A signal start event is visualized as a circle with a signal event symbol. The symbol is unfilled, to visualize the catching (receiving) behavior.

The XML representation of a signal start event is the normal start event declaration with a signalEventDefinition child-element:

An error start event can be used to trigger an Event Sub-Process. An error start event cannot be used for starting a process instance.

An error start event is always interrupting.

An error start event is visualized as a circle with an error event symbol. The symbol is unfilled, to visualize the catching (receiving) behavior.

The XML representation of an error start event is the normal start event declaration with an errorEventDefinition child-element:

A none end event means that the result thrown when the event is reached is unspecified. As such, the engine will not do anything extra besides ending the current path of execution.

A none end event is visualized as a circle with a thick border with no inner icon (no result type).

The XML representation of a none end event is the normal end event declaration, without any sub-element (other end event types all have a sub-element declaring the type).

When process execution arrives in an error end event, the current path of execution is ended and an error is thrown. This error can caught by a matching intermediate boundary error event. In case no matching boundary error event is found, an exception will be thrown.

An error end event is visualized as a typical end event (circle with thick border), with the error icon inside. The error icon is completely black, to indicate the throwing semantics.

And error end event is represented as an end event, with an errorEventDefinition child element.

The errorRef attribute can reference an error element that is defined outside the process:

The errorCode of the error will be used to find the matching catching boundary error event. If the errorRef does not match any defined error, then the errorRef is used as a shortcut for the errorCode. This is an Activiti specific shortcut. More concretely, following snippets are equivalent in functionality.

is equivalent with

Note that the errorRef must comply with the BPMN 2.0 schema, and must be a valid QName.

When a terminate end event is reached, the current process instance or sub-process will be terminated. Conceptually, when an execution arrives in a terminate end event, the first scope (process or sub-process) will be determined and ended. Note that in BPMN 2.0, a sub-process can be an embedded sub-process, call activity, event sub-process or transaction sub-process. This rule applies in general: when for example there is a multi-instance call activity or embedded subprocess, only that instance will be ended, the other instances and the process instance are not affected.

There is an optional attribute terminateAll that can be added. When true, regardless of the placement of the terminate end event in the process definition and regardless of being in a sub-process (even nested), the (root) process instance will be terminated.

A cancel end event visualized as a typical end event (circle with thick outline), with a full black circle inside.

A terminate end event is represented as an end event, with a terminateEventDefinition child element.

Note that the terminateAll attribute is optional (and false by default).

The cancel end event can only be used in combination with a bpmn transaction subprocess. When the cancel end event is reached, a cancel event is thrown which must be caught by a cancel boundary event. The cancel boundary event then cancels the transaction and triggers compensation.

A cancel end event visualized as a typical end event (circle with thick outline), with the cancel icon inside. The cancel icon is completely black, to indicate the throwing semantics.

A cancel end event is represented as an end event, with a cancelEventDefinition child element.

A timer boundary event acts as a stopwatch and alarm clock. When an execution arrives in the activity where the boundary event is attached to, a timer is started. When the timer fires (e.g. after a specified interval), the activity is interrupted boundary event are followed.

A timer boundary event is visualized as a typical boundary event (i.e. circle on the border), with the timer icon on the inside.

A timer boundary event is defined as a regular boundary event. The specific type sub-element is in this case a timerEventDefinition element.

Please refer to timer event definition for details on timer configuration.

In the graphical representation, the line of the circle is dotted as you can see in this example above:

A typical use case is sending an escalation email additionally but not interrupt the normal process flow.

Since BPMN 2.0 there is the difference between the interrupting and non interrupting timer event. The interrupting is the default. The non-interrupting leads to the original activity is not interrupted but the activity stays there. Instead an additional executions is created and send over the outgoing transition of the event. In the XML representation, the cancelActivity attribute is set to false:

Note: boundary timer events are only fired when the job or async executor is enabled (i.e. jobExecutorActivate or asyncExecutorActivate needs to be set to true in the activiti.cfg.xml, since the job and async executor are disabled by default).

There is a known issue regarding concurrency when using boundary events of any type. Currently, it is not possible to have multiple outgoing sequence flow attached to a boundary event (see issue ACT-47). A solution to this problem is to use one outgoing sequence flow that goes to a parallel gateway.

An intermediate catching error on the boundary of an activity, or boundary error event for short, catches errors that are thrown within the scope of the activity on which it is defined.

Defining a boundary error event makes most sense on an embedded subprocess, or a call activity, as a subprocess creates a scope for all activities inside the subprocess. Errors are thrown by error end events. Such an error will propagate its parent scopes upwards until a scope is found on which a boundary error event is defined that matches the error event definition.

When an error event is caught, the activity on which the boundary event is defined is destroyed, also destroying all current executions within (e.g. concurrent activities, nested subprocesses, etc.). Process execution continues following the outgoing sequence flow of the boundary event.

A boundary error event is visualized as a typical intermediate event (circle with smaller circle inside) on the boundary, with the error icon inside. The error icon is white, to indicate the catch semantics.

A boundary error event is defined as a typical boundary event:

As with the error end event, the errorRef references an error defined outside the process element:

The errorCode is used to match the errors that are caught:

Following example process shows how an error end event can be used. When the 'Review profitability' user task is completed by stating that not enough information is provided, an error is thrown. When this error is caught on the boundary of the subprocess, all active activities within the 'Review sales lead' subprocess are destroyed (even if 'Review customer rating' was not yet completed), and the 'Provide additional details' user task is created.

This process is shipped as example in the demo setup. The process XML and unit test can be found in the org.activiti.examples.bpmn.event.error package.

An attached intermediate catching signal on the boundary of an activity, or boundary signal event for short, catches signals with the same signal name as the referenced signal definition.

Note: contrary to other events like the boundary error event, a boundary signal event does not only catch signal events thrown from the scope it is attached to. On the contrary, a signal event has global scope (broadcast semantics) meaning that the signal can be thrown from any place, even from a different process instance.

Note: contrary to other events like an error event, a signal is not consumed if it is caught. If you have two active signal boundary events catching the same signal event, both boundary events are triggered, even if they are part of different process instances.

A boundary signal event is visualized as a typical intermediate event (Circle with smaller circle inside) on the boundary, with the signal icon inside. The signal icon is white (unfilled), to indicate the catch semantics.

A boundary signal event is defined as a typical boundary event:

See section on signal event definitions.

An attached intermediate catching message on the boundary of an activity, or boundary message event for short, catches messages with the same message name as the referenced message definition.

A boundary message event is visualized as a typical intermediate event (Circle with smaller circle inside) on the boundary, with the message icon inside. The message icon is white (unfilled), to indicate the catch semantics.

Note that boundary message event can be both interrupting (right hand side) and non-interrupting (left hand side).

A boundary message event is defined as a typical boundary event:

See section on message event definitions.

An attached intermediate catching cancel on the boundary of a transaction subprocess, or boundary cancel event for short, is triggered when a transaction is cancelled. When the cancel boundary event is triggered, it first interrupts all executions active in the current scope. Next, it starts compensation of all active compensation boundary events in the scope of the transaction. Compensation is performed synchronously, i.e. the boundary event waits before compensation is completed before leaving the transaction. When compensation is completed, the transaction subprocess is left using the sequence flow(s) running out of the cancel boundary event.

Note: Only a single cancel boundary event is allowed for a transaction subprocess.

Note: If the transaction subprocess hosts nested subprocesses, compensation is only triggered for subprocesses that have completed successfully.

Note: If a cancel boundary event is placed on a transaction subprocess with multi instance characteristics, if one instance triggers cancellation, the boundary event cancels all instances.

A cancel boundary event is visualized as a typical intermediate event (Circle with smaller circle inside) on the boundary, with the cancel icon inside. The cancel icon is white (unfilled), to indicate the catching semantics.

A cancel boundary event is defined as a typical boundary event:

Since the cancel boundary event is always interrupting, the cancelActivity attribute is not required.

An attached intermediate catching compensation on the boundary of an activity or compensation boundary event for short, can be used to attach a compensation handler to an activity.

The compensation boundary event must reference a single compensation handler using a directed association.

A compensation boundary event has a different activation policy from other boundary events. Other boundary events like for instance the signal boundary event are activated when the activity they are attached to is started. When the activity is left, they are deactivated and the corresponding event subscription is cancelled. The compensation boundary event is different. The compensation boundary event is activated when the activity it is attached to completes successfully. At this point, the corresponding subscription to the compensation events is created. The subscription is removed either when a compensation event is triggered or when the corresponding process instance ends. From this, it follows:

Note: the compensation boundary event is not supported on embedded subprocesses.

A compensation boundary event is visualized as a typical intermediate event (Circle with smaller circle inside) on the boundary, with the compensation icon inside. The compensation icon is white (unfilled), to indicate the catching semantics. In addition to a compensation boundary event, the following figure shows a compensation handler associated with the boundary event using a unidirectional association:

A compensation boundary event is defined as a typical boundary event:

Since the compensation boundary event is activated after the activity has completed successfully, the cancelActivity attribute is not supported.

A timer intermediate event acts as a stopwatch. When an execution arrives in catching event activity, a timer is started. When the timer fires (e.g. after a specified interval), the sequence flow going out of the timer intermediate event is followed.

A timer intermediate event is visualized as an intermediate catching event, with the timer icon on the inside.

A timer intermediate event is defined as an intermediate catching event. The specific type sub-element is in this case a timerEventDefinition element.

See timer event definitions for configuration details.

An intermediate catching signal event catches signals with the same signal name as the referenced signal definition.

Note: contrary to other events like an error event, a signal is not consumed if it is caught. If you have two active signal boundary events catching the same signal event, both boundary events are triggered, even if they are part of different process instances.

An intermediate signal catch event is visualized as a typical intermediate event (Circle with smaller circle inside), with the signal icon inside. The signal icon is white (unfilled), to indicate the catch semantics.

A signal intermediate event is defined as an intermediate catching event. The specific type sub-element is in this case a signalEventDefinition element.

See section on signal event definitions.

An intermediate catching message event catches messages with a specified name.

An intermediate catching message event is visualized as a typical intermediate event (Circle with smaller circle inside), with the message icon inside. The message icon is white (unfilled), to indicate the catch semantics.

A message intermediate event is defined as an intermediate catching event. The specific type sub-element is in this case a messageEventDefinition element.

See section on message event definitions.

An intermediate throwing signal event throws a signal event for a defined signal.

In Activiti, the signal is broadcast to all active handlers (i.e. all catching signal events). Signals can be published synchronous or asynchronous.

An intermediate signal throw event is visualized as a typical intermediate event (Circle with smaller circle inside), with the signal icon inside. The signal icon is black (filled), to indicate the throw semantics.

A signal intermediate event is defined as an intermediate throwing event. The specific type sub-element is in this case a signalEventDefinition element.

An asynchronous signal event would look like this:

See section on signal event definitions.

An intermediate throwing compensation event can be used to trigger compensation.

Triggering compensation: Compensation can either be triggered for a designated activity or for the scope which hosts the compensation event. Compensation is performed through execution of the compensation handler associated with an activity.

Note: If compensation is thrown within a scope which contains a subprocess and the subprocess contains activities with compensation handlers, compensation is only propagated to the subprocess if it has completed successfully when compensation is thrown. If some of the activities nested inside the subprocess have completed and have attached compensation handlers, the compensation handlers are not executed if the subprocess containing these activities is not completed yet. Consider the following example:

In this process we have two concurrent executions, one executing the embedded subprocess and one executing the "charge credit card" activity. Let’s assume both executions are started and the first concurrent execution is waiting for a user to complete the "review bookings" task. The second execution performs the "charge credit card" activity and an error is thrown, which causes the "cancel reservations" event to trigger compensation. At this point the parallel subprocess is not yet completed which means that the compensation event is not propagated to the subprocess and thus the "cancel hotel reservation" compensation handler is not executed. If the user task (and thus the embedded subprocess) completes before the "cancel reservations" is performed, compensation is propagated to the embedded subprocess.

Process variables: When compensating an embedded subprocess, the execution used for executing the compensation handlers has access to the local process variables of the subprocess in the state they were in when the subprocess completed execution. To achieve this, a snapshot of the process variables associated with the scope execution (execution created for executing the subprocess) is taken. Form this, a couple of implications follow:

Current limitations:

An intermediate compensation throw event is visualized as a typical intermediate event (Circle with smaller circle inside), with the compensation icon inside. The compensation icon is black (filled), to indicate the throw semantics.

A compensation intermediate event is defined as an intermediate throwing event. The specific type sub-element is in this case a compensateEventDefinition element.

In addition, the optional argument activityRef can be used to trigger compensation of a specific scope / activity:

A sequence flow can have a condition defined on it. When a BPMN 2.0 activity is left, the default behavior is to evaluate the conditions on the outgoing sequence flow. When a condition evaluates to true, that outgoing sequence flow is selected. When multiple sequence flow are selected that way, multiple executions will be generated and the process will be continued in a parallel way.

Note: the above holds for BPMN 2.0 activities (and events), but not for gateways. Gateways will handle sequence flow with conditions in specific ways, depending on the gateway type.

A conditional sequence flow is visualized as a regular sequence flow, with a small diamond at the beginning. The condition expression is shown next to the sequence flow.

A conditional sequence flow is represented in XML as a regular sequence flow, containing a conditionExpression sub-element. Note that for the moment only tFormalExpressions are supported, Omitting the xsi:type="" definition will simply default to this only supported type of expressions.

Currently conditionalExpressions can only be used with UEL, detailed info about these can be found in section Expressions. The expression used should resolve to a boolean value, otherwise an exception is thrown while evaluating the condition.

The Activiti distribution contains the following example process using value and method expressions (see org.activiti.examples.bpmn.expression):

All BPMN 2.0 tasks and gateways can have a default sequence flow. This sequence flow is only selected as the outgoing sequence flow for that activity if and only if none of the other sequence flow could be selected. Conditions on a default sequence flow are always ignored.

A default sequence flow is visualized as a regular sequence flow, with a slash marker at the beginning.

A default sequence flow for a certain activity is defined by the default attribute on that activity. The following XML snippet shows for example an exclusive gateway that has as default sequence flow flow 2. Only when conditionA and conditionB both evaluate to false, will it be chosen as outgoing sequence flow for the gateway.

Which corresponds with the following graphical representation:

An exclusive gateway (also called the XOR gateway or more technical the exclusive data-based gateway), is used to model a decision in the process. When the execution arrives at this gateway, all outgoing sequence flow are evaluated in the order in which they are defined. The sequence flow which condition evaluates to true (or which doesn’t have a condition set, conceptually having a 'true' defined on the sequence flow) is selected for continuing the process.

Note that the semantics of outgoing sequence flow is different to that of the general case in BPMN 2.0. While in general all sequence flow which condition evaluates to true are selected to continue in a parallel way, only one sequence flow is selected when using the exclusive gateway. In case multiple sequence flow have a condition that evaluates to true, the first one defined in the XML (and only that one!) is selected for continuing the process. If no sequence flow can be selected, an exception will be thrown.

An exclusive gateway is visualized as a typical gateway (i.e. a diamond shape) with an X icon inside, referring to the XOR semantics. Note that a gateway without an icon inside defaults to an exclusive gateway. The BPMN 2.0 specification does not allow mixing the diamond with and without an X in the same process definition.

The XML representation of an exclusive gateway is straight-forward: one line defining the gateway and condition expressions defined on the outgoing sequence flow. See the section on conditional sequence flow to see which options are available for such expressions.

Take for example the following model:

Which is represented in XML as follows:

Gateways can also be used to model concurrency in a process. The most straightforward gateway to introduce concurrency in a process model, is the Parallel Gateway, which allows to fork into multiple paths of execution or join multiple incoming paths of execution.

The functionality of the parallel gateway is based on the incoming and outgoing sequence flow:

Note that a parallel gateway can have both fork and join behavior, if there are multiple incoming and outgoing sequence flow for the same parallel gateway. In that case, the gateway will first join all incoming sequence flow, before splitting into multiple concurrent paths of executions.

An important difference with other gateway types is that the parallel gateway does not evaluate conditions. If conditions are defined on the sequence flow connected with the parallel gateway, they are simply neglected.

A parallel gateway is visualized as a gateway (diamond shape) with the plus symbol inside, referring to the AND semantics.

Defining a parallel gateway needs one line of XML:

The actual behavior (fork, join or both), is defined by the sequence flow connected to the parallel gateway.

For example, the model above comes down to the following XML:

In the above example, after the process is started, two tasks will be created:

When these two tasks are completed, the second parallel gateway will join the two executions and since there is only one outgoing sequence flow, no concurrent paths of execution will be created, and only the Archive Order task will be active.

Note that a parallel gateway does not need to be balanced (i.e. a matching number of incoming/outgoing sequence flow for corresponding parallel gateways). A parallel gateway will simply wait for all incoming sequence flow and create a concurrent path of execution for each outgoing sequence flow, not influenced by other constructs in the process model. So, the following process is legal in BPMN 2.0:

The Inclusive Gateway can be seen as a combination of an exclusive and a parallel gateway. Like an exclusive gateway you can define conditions on outgoing sequence flows and the inclusive gateway will evaluate them. But the main difference is that the inclusive gateway can take more than one sequence flow, like the parallel gateway.

The functionality of the inclusive gateway is based on the incoming and outgoing sequence flow:

Note that an inclusive gateway can have both fork and join behavior, if there are multiple incoming and outgoing sequence flow for the same inclusive gateway. In that case, the gateway will first join all incoming sequence flows that have a process token, before splitting into multiple concurrent paths of executions for the outgoing sequence flows that have a condition that evaluates to true.

An inclusive gateway is visualized as a gateway (diamond shape) with the circle symbol inside.

Defining an inclusive gateway needs one line of XML:

The actual behavior (fork, join or both), is defined by the sequence flows connected to the inclusive gateway.

For example, the model above comes down to the following XML:

In the above example, after the process is started, two tasks will be created if the process variables paymentReceived == false and shipOrder == true. In case only one of these process variables equals to true only one task will be created. If no condition evaluates to true and exception is thrown. This can be prevented by specifying a default outgoing sequence flow. In the following example one task will be created, the ship order task:

When this task is completed, the second inclusive gateway will join the two executions and since there is only one outgoing sequence flow, no concurrent paths of execution will be created, and only the Archive Order task will be active.

Note that an inclusive gateway does not need to be balanced (i.e. a matching number of incoming/outgoing sequence flow for corresponding inclusive gateways). An inclusive gateway will simply wait for all incoming sequence flow and create a concurrent path of execution for each outgoing sequence flow, not influenced by other constructs in the process model.

The Event-based Gateway allows to take a decision based on events. Each outgoing sequence flow of the gateway needs to be connected to an intermediate catching event. When process execution reaches an Event-based Gateway, the gateway acts like a wait state: execution is suspended. In addition, for each outgoing sequence flow, an event subscription is created.

Note the sequence flows running out of an Event-based Gateway are different from ordinary sequence flows. These sequence flows are never actually "executed". On the contrary, they allow the process engine to determine which events an execution arriving at an Event-based Gateway needs to subscribe to. The following restrictions apply:

An Event-based Gateway is visualized as a diamond shape like other BPMN gateways with a special icon inside.

The XML element used to define an Event-based Gateway is eventBasedGateway.

The following process is an example of a process with an Event-based Gateway. When the execution arrives at the Event-based Gateway, process execution is suspended. In addition, the process instance subscribes to the alert signal event and created a timer which fires after 10 minutes. This effectively causes the process engine to wait for ten minutes for a signal event. If the signal occurs within 10 minutes, the timer is cancelled and execution continues after the signal. If the signal is not fired, execution continues after the timer and the signal subscription is cancelled.

A user task is used to model work that needs to be done by a human actor. When the process execution arrives at such a user task, a new task is created in the task list of the user(s) or group(s) assigned to that task.

A user task is visualized as a typical task (rounded rectangle), with a small user icon in the left upper corner.

A user task is defined in XML as follows. The id attribute is required, the name attribute is optional.

A user task can have also a description. In fact any BPMN 2.0 element can have a description. A description is defined by adding the documentation element.

The description text can be retrieved from the task in the standard Java way:

Each task has a field, indicating the due date of that task. The Query API can be used to query for tasks that are due on, before or after a certain date.

There is an activity extension which allows you to specify an expression in your task-definition to set the initial due date of a task when it is created. The expression should always resolve to a java.util.Date, java.util.String (ISO8601 formatted), ISO8601 time-duration (e.g. PT50M) or null. For example, you could use a date that was entered in a previous form in the process or calculated in a previous Service Task. In case a time-duration is used, the due-date is calculated based on the current time, incremented by the given period. For example, when "PT30M" is used as dueDate, the task is due in thirty minutes from now.

The due date of a task can also be altered using the TaskService or in TaskListeners using the passed DelegateTask.

A user task can be directly assigned to a user. This is done by defining a humanPerformer sub element. Such a humanPerformer definition needs a resourceAssignmentExpression that actually defines the user. Currently, only formalExpressions are supported.

Only one user can be assigned as human performer to the task. In Activiti terminology, this user is called the assignee. Tasks that have an assignee are not visible in the task lists of other people and can be found in the so-called personal task list of the assignee instead.

Tasks directly assigned to users can be retrieved through the TaskService as follows:

Tasks can also be put in the so-called candidate task list of people. In that case, the potentialOwner construct must be used. The usage is similar to the humanPerformer construct. Do note that it is required to define for each element in the formal expression to specify if it is a user or a group (the engine cannot guess this).

Tasks defines with the potential owner construct, can be retrieved as follows (or a similar TaskQuery usage as for the tasks with an assignee):

This will retrieve all tasks where kermit is a candidate user, i.e. the formal expression contains user(kermit). This will also retrieve all tasks that are assigned to a group where kermit is a member of (e.g. group(management), if kermit is a member of that group and the Activiti identity component is used). The groups of a user are resolved at runtime and these can be managed through the IdentityService.

If no specifics are given whether the given text string is a user or group, the engine defaults to group. So the following would be the same as when group(accountancy) was declared.

It is clear that user and group assignments are quite cumbersome for use cases where the assignment is not complex. To avoid these complexities, custom extensions on the user task are possible.

This is exactly the same as using a humanPerformer construct as defined above.

This is exactly the same as using a potentialOwner construct as defined above. Note that it is not required to use the user(kermit) declaration as is the case with the potential owner construct, since the attribute can only be used for users.

This is exactly the same as using a potentialOwner construct as defined above. Note that it is not required to use the group(management) declaration as is the case with the potential owner construct, since the attribute can only be used for groups.

Note: Although Activiti provides an identity management component, which is exposed through the IdentityService, no check is done whether a provided user is known by the identity component. This allows Activiti to integrate with existing identity management solutions when it is embedded into an application.

[EXPERIMENTAL]

The BPMN standard supports a single assigned user or humanPerformer or a set of users that form a potential pool of potentialOwners as defined in User assignment. In addition, Activiti defines extension attribute elements for the User Task that can represent the task assignee or candidate owner.

The supported Activiti identity link types are:

The BPMN standard and Activiti example authorization identities are user and group. As mentioned in the previous section, the Activiti identity management implementation is not intended for production use, but should be extended depending upon the supported authorization scheme.

If additional link types are required, custom resources can be defined as extension elements with the following syntax:

The custom link expressions are added to the TaskDefinition class:

which are populated at runtime by the UserTaskActivityBehavior handleAssignments method.

Finally, the IdentityLinkType class must be extended to support the custom identity link types:

In case the previous approaches are not sufficient, it is possible to delegate to custom assignment logic using a task listener on the create event:

The DelegateTask that is passed to the TaskListener implementation, allows to set the assignee and candidate-users/groups:

When using Spring it is possible to use the custom assignment attributes as described in the section above, and delegate to a Spring bean using a task listener with an expression that listens to task create events. In the following example, the assignee will be set by calling the findManagerOfEmployee on the ldapService Spring bean. The emp parameter that is passed, is a process variable>.

This also works similar for candidate users and groups:

Note that this will only work if the return type of the invoked methods is String or Collection<String> (for candidate users and groups):

A script task is an automatic activity. When a process execution arrives at the script task, the corresponding script is executed.

A script task is visualized as a typical BPMN 2.0 task (rounded rectangle), with a small script icon in the top-left corner of the rectangle.

A script task is defined by specifying the script and the scriptFormat.

The value of the scriptFormat attribute must be a name that is compatible with the JSR-223 (scripting for the Java platform). By default JavaScript is included in every JDK and as such doesn’t need any additional jars. If you want to use another (JSR-223 compatible) scripting engine, it is sufficient to add the corresponding jar to the classpath and use the appropriate name. For example, the Activiti unit tests often use Groovy because the syntax is pretty similar to that of Java.

Do note that the Groovy scripting engine is bundled with the groovy-all jar. Before version 2.0, the scripting engine was part of the regular Groovy jar. As such, one must now add following dependency:

All process variables that are accessible through the execution that arrives in the script task, can be used within the script. In the example, the script variable 'inputArray' is in fact a process variable (an array of integers).

It’s also possible to set process variables in a script, simply by calling execution.setVariable("variableName", variableValue). By default, no variables are stored automatically (Note: before Activiti 5.12 this was the case!). It is possible to automatically store any variable defined in the script (e.g. sum in the example above) by setting the property autoStoreVariables on the scriptTask to true. However, the best practice is not to do this and use an explicit execution.setVariable() call, as on some recent versions of the JDK auto storing of variables does not work for some scripting languages. See this link for more details.

The default of this parameter is false, meaning that if the parameter is omitted from the script task definition, all the declared variables will only exist during the duration of the script.

Example on how to set a variable in a script:

Note: the following names are reserved and cannot be used as variable names: out, out:print, lang:import, context, elcontext.

The return value of a script task can be assigned to an already existing or to a new process variable by specifying the process variable name as a literal value for the 'activiti:resultVariable' attribute of a script task definition. Any existing value for a specific process variable will be overwritten by the result value of the script execution. When not specifying a result variable name, the script result value gets ignored.

In the above example, the result of the script execution (the value of the resolved expression '#{echo}') is set to the process variable named 'myVar' after the script completes.

It is also possible when using javascript as scripting language to use secure scripting. See the secure scripting section.

A Java service task is used to invoke an external Java class.

A service task is visualized as a rounded rectangle with a small gear icon in the top-left corner.

There are 4 ways of declaring how to invoke Java logic:

To specify a class that is called during process execution, the fully qualified classname needs to be provided by the activiti:class attribute.

See the implementation section for more details on how to use such a class.

It is also possible to use an expression that resolves to an object. This object must follow the same rules as objects that are created when the activiti:class attribute is used (see further).

Here, the delegateExpressionBean is a bean that implements the JavaDelegate interface, defined in for example the Spring container.

To specify a UEL method expression that should be evaluated, use attribute activiti:expression.

Method printMessage (without parameters) will be called on the named object called printer.

It’s also possible to pass parameters with an method used in the expression.

Method printMessage will be called on the object named printer. The first parameter passed is the DelegateExecution, which is available in the expression context by default available as execution. The second parameter passed, is the value of the variable with name myVar in the current execution.

To specify a UEL value expression that should be evaluated, use attribute activiti:expression.

The getter method of property ready, getReady (without parameters), will be called on the named bean called split. The named objects are resolved in the execution’s process variables and (if applicable) in the Spring context.

To implement a class that can be called during process execution, this class needs to implement the org.activiti.engine.delegate.JavaDelegate interface and provide the required logic in the execute method. When process execution arrives at this particular step, it will execute this logic defined in that method and leave the activity in the default BPMN 2.0 way.

Let’s create for example a Java class that can be used to change a process variable String to uppercase. This class needs to implement the org.activiti.engine.delegate.JavaDelegate interface, which requires us to implement the execute(DelegateExecution) method. It’s this operation that will be called by the engine and which needs to contain the business logic. Process instance information such as process variables and other can be accessed and manipulated through the DelegateExecution interface (click on the link for a detailed Javadoc of its operations).

Note: there will be only one instance of that Java class created for the serviceTask it is defined on. All process-instances share the same class instance that will be used to call execute(DelegateExecution). This means that the class must not use any member variables and must be thread-safe, since it can be executed simultaneously from different threads. This also influences the way Field injection is handled.

The classes that are referenced in the process definition (i.e. by using activiti:class) are NOT instantiated during deployment. Only when a process execution arrives for the first time at the point in the process where the class is used, an instance of that class will be created. If the class cannot be found, an ActivitiException will be thrown. The reasoning for this is that the environment (and more specifically the classpath) when you are deploying is often different from the actual runtime environment. For example when using ant or the business archive upload in Activiti Explorer to deploy processes, the classpath does not contain the referenced classes.

[INTERNAL: non-public implementation classes] It is also possible to provide a class that implements the org.activiti.engine.impl.pvm.delegate.ActivityBehavior interface. Implementations have then access to the more powerful ActivityExecution that for example also allows to influence the control flow of the process. Note however that this is not a very good practice, and should be avoided as much as possible. So, it is advised to use the ActivityBehavior interface only for advanced use cases and if you know exactly what you’re doing.

It’s possible to inject values into the fields of the delegated classes. The following types of injection are supported:

If available, the value is injected through a public setter method on your delegated class, following the Java Bean naming conventions (e.g. field firstName has setter setFirstName(…​)). If no setter is available for that field, the value of private member will be set on the delegate. SecurityManagers in some environments don’t allow modifying private fields, so it’s safer to expose a public setter-method for the fields you want to have injected.

Regardless of the type of value declared in the process-definition, the type of the setter/private field on the injection target should always be org.activiti.engine.delegate.Expression. When the expression is resolved it can be cast to the appropriate type.

Field injection is supported when using the 'actviiti:class' attribute. Field injection is also possible when using the activiti:delegateExpression attribute, however special rules with regards to thread-safety apply (see next section).

The following code snippet shows how to inject a constant value into a field declared on the class. Note that we need to declare a extensionElements XML element before the actual field injection declarations, which is a requirement of the BPMN 2.0 XML Schema.

The class ToUpperCaseFieldInjected has a field text which is of type org.activiti.engine.delegate.Expression. When calling text.getValue(execution), the configured string value Hello World will be returned:

Alternatively, for longs texts (e.g. an inline e-mail) the 'activiti:string' sub element can be used:

To inject values that are dynamically resolved at runtime, expressions can be used. Those expressions can use process variables, or Spring defined beans (if Spring is used). As noted in Service Task Implementation, an instance of the Java class is shared among all process-instances in a service task when using the activiti:class attribute. To have dynamic injection of values in fields, you can inject value and method expressions in a org.activiti.engine.delegate.Expression which can be evaluated/invoked using the DelegateExecution passed in the execute method.

The example class below uses the injected expressions and resolves them using the current DelegateExecution. A generBean method call is used while passing the gender variable. Full code and test can be found in org.activiti.examples.bpmn.servicetask.JavaServiceTaskTest.testExpressionFieldInjection

Alternatively, you can also set the expressions as an attribute instead of a child-element, to make the XML less verbose.

In general, using service tasks with Java delegates and field injections are thread-safe. However, there are a few situations where thread-safety is not guaranteed, depending on the setup or environment Activiti is running in.

When using the activiti:class attribute, using field injection is always thread safe. For each service task that references a certain class, a new instance will be instantiated and fields will be injected once when the instance is created. Reusing the same class in multiple times in different tasks or process definitions is no problem.

When using the activiti:expression attribute, using field injection is not possible. Parameters are passed via method calls and these are always thread-safe.

When using the activiti:delegateExpression attribute, the thread-safety of the delegate instance will depend on how the expression is resolved. If the delegate expression is reused in various tasks and/or process definitions and the expression always returns the same instance, using field injection is not thread-safe. Let’s look at a few examples to clarify.

Suppose the expression is ${factory.createDelegate(someVariable)}, where factory is a Java bean known to the engine (for example a Spring bean when using the Spring integration) that creates a new instance each time the expression is resolved. When using field injection in this case, there is no problem with regards to thread-safety: each time the expression is resolved, the fields are injected on this new instance.

However, suppose the expression is ${someJavaDelegateBean} that resolves to an implementation of the JavaDelegate class and we’re running in an environment that creates singleton instances of each bean (like Spring, but many others too). When using this expression in different tasks and/or process definitions, the expression will always be resolved to the same instance. In this case, using field injection is not thread-safe. For example:

This example snippet has two service tasks that use the same delegate expression, but injects different values for the Expression field. If the expression resolves to the same instance, there can be race conditions in concurrent scenarios when it comes to injecting the field someField when the processes are executed.

The easiest solution to solve this, is to either

As of Activiti version 5.21, the process engine configuration can be configured in a way to disable the use of field injection on delegate epxressions, by setting the value of the delegateExpressionFieldInjectionMode property (which takes one of the values in the org.activiti.engine.imp.cfg.DelegateExpressionFieldInjectionMode enum).

Following settings are possible:

For example, suppose that we’re using MIXED mode and we’re using the Spring integration. Suppose that we have following beans in the Spring configuration:

The first bean is a regular Spring bean and thus a singleton. The second one has prototype as scope, and the Spring container will return a new instance every time the bean is requested.

Given following process definition:

We’ve got four service tasks, where the first and the second use the ${prototypeDelegateExpressionBean} delegate expression and the third and fourth use the ${singletonDelegateExpressionBean} delegate expression.

Let’s look at the prototype bean first:

When we check the INSTANCE_COUNT after running a process instance of the process definition above, we’ll get two back, as a new instance is created every time ${prototypeDelegateExpressionBean} is resolved. Fields can be injected without any problem here and we can see the three Expression member fields here.

The singleton bean, however, looks slightly different:

The INSTANCE_COUNT will always be one here, as it is a singleton. In this delegate, there are no Expression member fields. This is possible since we’re running in MIXED mode. In COMPATIBILITY mode, this would throw an exception as it expects the member fields to be there. DISABLED mode would also work for this bean, but it would disallow the use the prototype bean above that does use field injection.

In this delegate code, the org.activiti.engine.delegate.DelegateHelper class is used, that has some useful utility methods to execute the same logic, but in a thread-safe way when the delegate is a singleton. Instead of injecting the Expression, it is fetched via the getFieldExpression method. This means that when it comes to the service task xml, the fields are defined exactly the same as for the singleton bean. If you look at the xml snippet above, you can see they are equal in definition and only the implementation logic differs.

(Technical note: the getFieldExpression will introspect the BpmnModel and create the Expression on the fly when the method is executed, making it thread-safe)

Where testExecutionListener resolves to an instance implementing the ExecutionListener interface:

The return value of a service execution (for service task using expression only) can be assigned to an already existing or to a new process variable by specifying the process variable name as a literal value for the 'activiti:resultVariable' attribute of a service task definition. Any existing value for a specific process variable will be overwritten by the result value of the service execution. When not specifying a result variable name, the service execution result value gets ignored.

In the example above, the result of the service execution (the return value of the 'doSomething()' method invocation on an object that is made available under the name 'myService' either in the process variables or as a Spring bean) is set to the process variable named 'myVar' after the service execution completes.

When custom logic is executed, it is often required to catch certain business exceptions and handle them inside the surrounding process. Activiti provides different options to do that.

For some use cases, it might be needed to use the Activiti services from within a Java service task (e.g. starting a process instance through the RuntimeService, if the callActivity doesn’t suit your needs). The org.activiti.engine.delegate.DelegateExecution allows to easily use these services through the org.activiti.engine.EngineServices interface:

All of the Activiti service API’s are available through this interface.

All data changes that occur as an effect of using these API calls, will be part of the current transaction. This also works in environments with dependency injection like Spring and CDI with or without a JTA enabled datasource. For example, the following snippet of code will do the same as the snippet above, but now the RuntimeService is injected rather than it is being fetched through the org.activiti.engine.EngineServices interface.

Important technical note: since the service call is being done as part of the current transaction any data that was produced or altered before the service task is executed, is not yet flushed to the database. All API calls work on the database data, which means that these uncommitted changes are not be visible within the api call of the service task.

A Web Service task is used to synchronously invoke an external Web service.

A Web Service task is visualized the same as a Java service task.

To use a Web service we need to import its operations and complex types. This can be done automatically by using the import tag pointing to the WSDL of the Web service:

The previous declaration tells Activiti to import the definitions but it doesn’t create the item definitions and messages for you. Let’s suppose we want to invoke a specific method called prettyPrint, therefore we will need to create the corresponding message and item definitions for the request and response messages:

Before declaring the service task, we have to define the BPMN interfaces and operations that actually reference the Web service ones. Basically, we define and interface and the required operation’s. For each operation we reuse the previous defined message for in and out. For example, the following declaration defines the counter interface and the prettyPrintCountOperation operation:

Then we can declare a Web Service Task by using the ##WebService implementation and a reference to the Web service operation.

Unless we are using the simplistic approach for data input and output associations (See below), each Web Service Task needs to declare an IO Specification which states which are the inputs and outputs of the task. The approach is pretty straightforward and BPMN 2.0 complaint, for our prettyPrint example we define the input and output sets according to the previously declared item definitions:

There are 2 ways of specifying data input associations:

To specify the data input association using expressions we need to define the source and target items and specify the corresponding assignments between the fields of each item. In the following example we assign prefix and suffix fields of the items:

On the other hand we can use the simplistic approach which is much more simple. The sourceRef element is an Activiti variable name and the targetRef element is a property of the item definition. In the following example we assign to the prefix field the value of the variable PrefixVariable and to the suffix field the value of the variable SuffixVariable.

There are 2 ways of specifying data out associations:

To specify the data out association using expressions we need to define the target variable and the source expression. The approach is pretty straightforward and similar data input associations:

On the other hand we can use the simplistic approach which is much more simple. The sourceRef element is a property of the item definition and the targetRef element is an Activiti variable name. The approach is pretty straightforward and similar data input associations:

A Business Rule task is used to synchronously execute one or more rules. Activiti uses Drools Expert, the Drools rule engine to execute business rules. Currently, the .drl files containing the business rules have to be deployed together with the process definition that defines a business rule task to execute those rules. This means that all .drl files that are used in a process have to be packaged in the process BAR file like for example the task forms. For more information about creating business rules for Drools Expert please refer to the Drools documentation at JBoss Drools

If you want to plug in your implementation of the rule task, e.g. because you want to use Drools differently or you want to use a completely different rule engine, then you can use the class or expression attribute on the BusinessRuleTask and it will behave exactly like a ServiceTask

A Business Rule task is visualized the with a table icon.

To execute one or more business rules that are deployed in the same BAR file as the process definition, we need to define the input and result variables. For the input variable definition a list of process variables can be defined separated by a comma. The output variable definition can only contain one variable name that will be used to store the output objects of the executed business rules in a process variable. Note that the result variable will contain a List of objects. If no result variable name is specified by default org.activiti.engine.rules.OUTPUT is used.

The following business rule task executes all business rules deployed with the process definition:

The business rule task can also be configured to execute only a defined set of rules from the deployed .drl files. A list of rule names separated by a comma must be specified for this.

In this case only rule1 and rule2 are executed.

You can also define a list of rules that should be excluded from execution.

In this case all rules deployed in the same BAR file as the process definition will be executed, except for rule1 and rule2.

As mentioned earlier another option is to hook in the implementation of the BusinessRuleTask yourself:

Now the BusinessRuleTask behaves exactly like a ServiceTask, but still keeps the BusinessRuleTask icon to visualize that we do business rule processing here.

The Activiti engine sends e-mails trough an external mail server with SMTP capabilities. To actually send e-mails, the engine needs to know how to reach the mail server. Following properties can be set in the activiti.cfg.xml configuration file:

The Email task is implemented as a dedicated Service Task and is defined by setting 'mail' for the type of the service task.

The Email task is configured by field injection. All the values for these properties can contain EL expression, which are resolved at runtime during process execution. Following properties can be set:

The following XML snippet shows an example of using the Email Task.

with the following result:

The Mule task is implemented as a dedicated Service Task and is defined by setting 'mule' for the type of the service task.

The Mule task is configured by field injection. All the values for these properties can contain EL expression, which are resolved at runtime during process execution. Following properties can be set:

The following XML snippet shows an example of using the Mule Task.

The Camel task is implemented as a dedicated Service Task and is defined by setting 'camel' for the type of the service task.

The process definition itself needs nothing else then the camel type definition on a service task. The integration logic is all delegated to the Camel container. By default the Activiti Engine looks for a camelContext bean in the Spring container. The camelContext bean defines the Camel routes that will be loaded by the Camel container. In the following example the routes are loaded from a specific Java package, but you can also define routes directly in the Spring configuration itself.

For more documentation about Camel routes you can look on the Camel website. The basic concepts are demonstrated through a few small samples here in this document. In the first sample, we will do the simplest form of Camel call from an Activiti workflow. Let’s call it SimpleCamelCall.

If you want to define multiple Camel context beans and/or want to use a different bean name, this can be overridden on the Camel task definition like this:

All the files related to this example can be found in org.activiti.camel.examples.simpleCamelCall package of activiti-camel module. The target is simply activating a specific camel route. First of all we need an Spring context which contains the introduction to the routes as mentioned previously. This part of the file serves this purpose:

The route just logs the message body and nothing more. Notice the format of the from endpoint. It is consisted of three parts:

Ok, our route is now properly configured and accessible to the Camel. Now comes the workflow part. The workflow looks like:

Our example worked but nothing is really transferred between Camel and Activiti and there is not much merit in it. In this example we try to send and receive data to and from Camel. We send a string, camel concatenates something to it and returns back the result. The sender part is trivial, we send our message in form of a variable to Camel Task. Here is our caller code:

The variable "input" is actually the input for the Camel route and outputMap is there to capture the result back from Camel. The process should be something like this:

Note that SaveOutput Service task, stores the value of "Output" variable from context to the previously mentioned OutputMap. Now we have to know how the variables are send to Camel and returned back. Here comes the notion of Camel behaviour into the play. The way variables are communicated to Camel is configurable via CamelBehavior. Here we use Default one in our sample, a short description of the other ones comes afterwards. With such a code you can configure the desired camel behaviour:

If you do not specify and specific behaviour then, org.activiti.camel.impl.CamelBehaviorDefaultImpl will be set. This behaviour copies the variables to Camel properties of the same name. In return regardless of selected behaviour, if the camel message body is a map, then each of its elements is copied as a variable, else the whole object is copied into a specific variable with the name of "camelBody". Knowing that, this camel route concludes our second example:

In this route, the string "world" is concatenated to the end of property named "input" and the result will be in the message body. It is accessible by checking "camelBody" variable in the java service task and copied to "outputMap" and checked in test case. Now that the example on its default behaviour works, lets see what are the other possibilities. In starting every camel route, the Process Instance ID will be copied into a camel property with the specific name of "PROCESS_ID_PROPERTY". It is later used for correlating the process instance and camel route. Also it can be exploited in the Camel route.

There are three different behaviours already available out of the box in Activiti. The behaviour can be overwritten by a specific phrase in the route URL. Here is an example of overriding the already defined behaviour in URL:

the following table provides an overview of three available camel behaviours:

The above table explains how Activiti variables are going to be transferred to Camel. The following table explains how the Camel variables are returned back to Activiti. This can only be configured in route URLs.

What is mentioned above about passing variables, only holds for start side of the variable transfer, in both directions from Camel to Activiti and vice versa.
It is important to notice that because of special non blocking behavior of Activiti, variables are not automatically returned back from Activiti to Camel. For that to happen, a special syntax is available. There can be one or more parameters in Camel route URL in format of var.return.someVariableName. All variables having a name equal to one of these parameters without var.return part, will be considered as output variables and will be copied back as camel properties with the same names.
For example in a route like:

Activiti variable with the name of exampleVar will be considered as output variable and will be copied back as a property in camel with the same name.

Previous examples were all synchronous. The workflow stops, until the camel route is concluded and returned. In some cases, we might need the Activiti workflow to continue. For such purposes the asynchronous capability of the Camel service task is useful. You can make use of this feature by setting the async property of the Camel service task to true.

By setting this feature the specified Camel route is activated asynchronously by the Activiti job executor. When you define a queue in the Camel route the Activiti process will continue with the activities after the Camel service task. The Camel route will be executed fully asynchronously from the process execution. If you want to wait for a response of the Camel service task somewhere in your process definition, you can use a receive task.

The process instance will wait until a signal is received, for example from Camel. In Camel you can send a signal to the process instance by sending a message to the proper Activiti endpoint.

In our all previous examples Activiti workflow started first and the Camel route was started within workflow. It is also possible from the other side. It is possible that a workflow is instantiated from an already started camel route. It is very similar to signalling receive task, except that the last part is not there. Here is a sample route:

as you see the url has two parts, the first is constant string "activiti" and the second name is the name of the process. Obviously the process should already be deployed and startable by engine configuration.

It is also possible to set the initiator of the process to some authenticated user id that is provided in a Camel header. To achieve this first of all an initiator variable must be specified in the process definition:

Then given that the user id is contained in a Camel header named CamelProcessInitiatorHeader the Camel route could be defined as follows:

A Manual Task defines a task that is external to the BPM engine. It is used to model work that is done by somebody, which the engine does not need to know of, nor is there a system or UI interface. For the engine, a manual task is handled as a pass-through activity, automatically continuing the process from the moment process execution arrives into it.

A manual task is visualized as a rounded rectangle, with a little hand icon in the upper left corner

A Receive Task is a simple task that waits for the arrival of a certain message. Currently, we have only implemented Java semantics for this task. When process execution arrives at a Receive Task, the process state is committed to the persistence store. This means that the process will stay in this wait state, until a specific message is received by the engine, which triggers the continuation of the process past the Receive Task.

A Receive Task is visualized as a task (rounded rectangle) with a message icon in the top left corner. The message is white (a black message icon would have send semantics)

To continue a process instance that is currently waiting at such a Receive Task, the runtimeService.signal(executionId) must be called using the id of the execution that arrived in the Receive Task. The following code snippet shows how this works in practice:

The shell task allows to run shell scripts and commands. Note that the Shell task is not an official task of BPMN 2.0 spec (and it does not have a dedicated icon as a consequence).

The shell task is implemented as a dedicated Service Task and is defined by setting 'shell' for the type of the service task.

The Shell task is configured by field injection. All the values for these properties can contain EL expression, which are resolved at runtime during process execution. Following properties could be set:

The following XML snippet shows an example of using the shell Task. It runs shell script "cmd /c echo EchoTest", waits for it to be terminated and puts the result in resultVar

When using an execution listener that is configured with the class attribute, field injection can be applied. This is exactly the same mechanism as used Service task field injection, which contains an overview of the possibilities provided by field injection.

The fragment below shows a simple example process with an execution listener with fields injected.

The class ExampleFieldInjectedExecutionListener concatenates the 2 injected fields (one fixed an the other dynamic) and stores this in the process variable var.

Note that the same rules with regards to thread-safety apply as for service task. Please read the relevant section for more information.

A multi-instance activity is a way of defining repetition for a certain step in a business process. In programming concepts, a multi-instance matches the for each construct: it allows to execute a certain step or even a complete subprocess for each item in a given collection, sequentially or in parallel.

A multi-instance is a regular activity that has extra properties defined (so-called 'multi-instance characteristics'') which will cause the activity to be executed multiple times at runtime. Following activities can become a multi-instance activity:

A Gateway or Event cannot become multi-instance.

As required by the spec, each parent execution of the created executions for each instance will have following variables:

These values can be retrieved by calling the execution.getVariable(x) method.

Additionally, each of the created executions will have an execution-local variable (i.e. not visible for the other executions, and not stored on process instance level) :

If an activity is multi-instance, this is indicated by three short lines at the bottom of that activity. Three vertical lines indicates that the instances will be executed in parallel, while three horizontal lines indicate sequential execution.

To make an activity multi-instance, the activity xml element must have a multiInstanceLoopCharacteristics child element.

The isSequential attribute indicates if the instances of that activity are executed sequentially or parallel.

The number of instances are calculated once, when entering the activity. There are a few ways of configuring this. On way is directly specifying a number, by using the loopCardinality child element.

Expressions that resolve to a positive number are also possible:

Another way to define the number of instances, is to specify the name of a process variable which is a collection using the loopDataInputRef child element. For each item in the collection, an instance will be created. Optionally, it is possible to set that specific item of the collection for the instance using the inputDataItem child element. This is shown in the following XML example:

Suppose the variable assigneeList contains the values \[kermit, gonzo, fozzie\]. In the snippet above, three user tasks will be created in parallel. Each of the executions will have a process variable named assignee containing one value of the collection, which is used to assign the user task in this example.

The downside of the loopDataInputRef and inputDataItem is that 1) the names are pretty hard to remember and 2) due to the BPMN 2.0 schema restrictions they can’t contain expressions. Activiti solves this by offering the collection and elementVariable attributes on the multiInstanceCharacteristics:

A multi-instance activity ends when all instances are finished. However, it is possible to specify an expression that is evaluated every time one instance ends. When this expression evaluates to true, all remaining instances are destroyed and the multi-instance activity ends, continuing the process. Such an expression must be defined in the completionCondition child element.

In this example, there will be parallel instances created for each element of the assigneeList collection. However, when 60% of the tasks are completed, the other tasks are deleted and the process continues.

Since a multi-instance is a regular activity, it is possible to define a boundary event on its boundary. In case of an interrupting boundary event, when the event is caught, all instances that are still active will be destroyed. Take for example following multi-instance subprocess:

Here, all instances of the subprocess will be destroyed when the timer fires, regardless of how many instances there are or which inner activities are currently not yet completed.

(Valid for Activiti 5.18 and up)

There is a caveat when using execution listeners in combination with multi instance. Take for example the following snippet of BPMN 2.0 xml, which is defined on the same level as the multiInstanceLoopCharacteristics xml element is set:

For a normal BPMN activity, there would be an invocation of these listeners when the activity is started and ended.

However, when the activity is multi instance, the behavior is different:

The same reasoning applies for the end event:

For example:

In this example, suppose the assignees list has three items. The following happens at runtime:

Note that the same applies when the multiInstanceLoopCharacteristics are defined on something else than a subprocess too. For example in case the example above would be a simple userTask, the same reasoning still applies.

[EXPERIMENTAL]

If an activity is used for compensating the effects of another activity, it can be declared to be a compensation handler. Compensation handlers are not contained in normal flow and are only executed when a compensation event is thrown.

Compensation handlers must not have incoming or outgoing sequence flows.

A compensation handler must be associated with a compensation boundary event using a directed association.

If an activity is a compensation handler, the compensation event icon is displayed in the center bottom area. The following excerpt from a process diagram shows a service task with an attached compensation boundary event which is associated to a compensation handler. Notice the compensation handler icon in the bottom canter area of the "cancel hotel reservation" service task.

In order to declare an activity to be a compensation handler, we need to set the attribute isForCompensation to true:

A Sub-Process is an activity that contains other activities, gateways, events, etc. which on itself form a process that is part of the bigger process. A Sub-Process is completely defined inside a parent process (that’s why it’s often called an embedded Sub-Process).

Sub-Processes have two major use cases:

Using a Sub-Process does impose some constraints:

A Sub-Process is visualized as a typical activity, i.e. a rounded rectangle. In case the Sub-Process is collapsed, only the name and a plus-sign are displayed, giving a high-level overview of the process:

In case the Sub-Process is expanded, the steps of the Sub-Process are displayed within the Sub-Process boundaries:

One of the main reasons to use a Sub-Process, is to define a scope for a certain event. The following process model shows this: both the investigate software/investigate hardware tasks need to be done in parallel, but both tasks need to be done within a certain time, before Level 2 support is consulted. Here, the scope of the timer (i.e. which activities must be done in time) is constrained by the Sub-Process.

A Sub-Process is defined by the subprocess element. All activities, gateways, events, etc. that are part of the Sub-Process, need to be enclosed within this element.

The Event Sub-Process is new in BPMN 2.0. An Event Sub-Process is a subprocess that is triggered by an event. An Event Sub-Process can be added at the process level or at any subprocess level. The event used to trigger an event subprocess is configured using a start event. From this, it follows that none start events are not supported for Event Sub-Processes. An Event Sub-Process might be triggered using events like message events, error events, signal events, timer events, or compensation events. The subscription to the start event is created when the scope (process instance or subprocess) hosting the Event Sub-Process is created. The subscription is removed when the scope is destroyed.

An Event Sub-Process may be interrupting or non-interrupting. An interrupting subprocess cancels any executions in the current scope. A non-interrupting Event Sub-Process spawns a new concurrent execution. While an interrupting Event Sub-Process can only be triggered once for each activation of the scope hosting it, a non-interrupting Event Sub-Process can be triggered multiple times. The fact whether the subprocess is interrupting is configured using the start event triggering the Event Sub-Process.

An Event Sub-Process must not have any incoming or outgoing sequence flows. Since an Event Sub-Process is triggered by an event, an incoming sequence flow makes no sense. When an Event Sub-Process is ended, either the current scope is ended (in case of an interrupting Event Sub-Process), or the concurrent execution spawned for the non-interrupting subprocess is ended.

Current limitations:

An Event Sub-Process might be visualized as a an embedded subprocess with a dotted outline.

An Event Sub-Process is represented using XML in the same way as a an embedded subprocess. In addition the attribute triggeredByEvent must have the value true:

The following is an example of an Event Sub-Process triggered using an Error Start Event. The Event Sub-Process is located at the "process level", i.e. is scoped to the process instance:

This is how the Event Sub-Process would look like in XML:

As already stated, an Event Sub-Process can also be added to an embedded subprocess. If it is added to an embedded subprocess, it becomes an alternative to a boundary event. Consider the two following process diagrams. In both cases the embedded subprocess throws an error event. Both times the error is caught and handled using a user task.

as opposed to:

In both cases the same tasks are executed. However, there are differences between both modelling alternatives:

These two differences can help you decide whether a boundary event or an embedded subprocess is better suited for solving a particular process modeling / implementation problem.

A transaction subprocess is an embedded subprocess, which can be used to group multiple activities to a transaction. A transaction is a logical unit of work which allows to group a set of individual activities, such that they either succeed or fail collectively.

Possible outcomes of a transaction: A transaction can have three different outcomes:

The following diagram illustrates the three different outcomes:

Relation to ACID transactions: it is important not to confuse the bpmn transaction subprocess with technical (ACID) transactions. The bpmn transaction subprocess is not a way to scope technical transactions. In order to understand transaction management in Activiti, read the section on concurrency and transactions. A bpmn transaction is different from a technical transaction in the following ways:

Since bpmn transactions are long-running in nature, the lack of isolation and a rollback mechanism need to be dealt with differently. In practice, there is usually no better solution than to deal with these problems in a domain specific way:

To sum it up: while ACID transactions offer a generic solution to such problems (rollback, isolation levels and heuristic outcomes), we need to find domain specific solutions to these problems when implementing business transactions.

Current limitations:

Consistency on top of ACID transactions and optimistic concurrency: A bpmn transaction guarantees consistency in the sense that either all activities compete successfully, or if some activity cannot be performed, the effects of all other successful activities are compensated. So either way we end up in a consistent state. However, it is important to recognize that in Activiti, the consistency model for bpmn transactions is superposed on top of the consistency model for process execution. Activiti executes processes in a transactional way. Concurrency is addressed using optimistic locking. In Activiti, bpmn error, cancel and compensation events are built on top of the same acid transactions and optimistic locking. For example, a cancel end event can only trigger compensation if it is actually reached. It is not reached if some undeclared exception is thrown by a service task before. Or, the effects of a compensation handler cannot be committed if some other participant in the underlying ACID transaction sets the transaction to the state rollback-only. Or, when two concurrent executions reach a cancel end event, compensation might be triggered twice and fail with an optimistic locking exception. All of this is to say that when implementing bpmn transactions in Activiti, the same set of rules apply as when implementing "ordinary" processes and subprocesses. So to effectively guarantee consistency, it is important to implement processes in a way that does take the optimistic, transactional execution model into consideration.

An transaction subprocess might be visualized as a an embedded subprocess with a double outline.

A transaction subprocess is represented using xml using the transaction tag:

The following is an example of a transaction subprocess:

BPMN 2.0 makes a distinction between a regular subprocess, often also called embedded subprocess, and the call activity, which looks very similar. From a conceptual point of view, both will call a subprocess when process execution arrives at the activity.