Engine CDI Integration

Quarkus comes with a built-in solution for CDI (short for “Context and Dependency Injection”) called ArC, which is based on the Java CDI 4.0 standard. Quarkus ArC does not entirely cover the CDI 4.0 standard but only implements a subset of it.

The Camunda Engine offers CDI 4 integration with the camunda-engine-cdi-jakarta module. This module is integrated directly into the Quarkus Extension. You can learn more about the features and the programming model at CDI and Java EE Integration.

Limitations

Since Quarkus ArC does not aim to implement CDI 4.0 fully, you cannot use the full range of features the camunda-engine-cdi-jakarta module provides. Some features documented under CDI and Java EE Integration are unsupported or only work with restrictions. The limitations and differences are explained in more detail below.

Limited support of JUEL Expression Resolution

The camunda-engine-cdi-jakarta module allows referencing CDI beans and calling methods on CDI beans in model expression properties (e.g., camunda:expression, camunda:delegateExpression, etc.). Quarkus ArC currently doesn’t support the CDI API method javax.enterprise.inject.spi.BeanManager#getELResolver, which the engine uses to resolve method calls on CDI beans. This is why currently, only referencing CDI beans is supported.

Examples:

• Supported Expression: ${myService}
• Unsupported Expression: ${myService.checkCondition('foo')}

Limited support of scopes in the Contextual Programming Model

While the camunda-engine-cdi-jakarta module supports associating a process instance with Conversational Scope or Request Scope, Quarkus ArC only supports the Request Scope.

Configure Quarkus to allow setting variables when a @StartProcess annotated method is called

The camunda-engine-cdi-jakarta module allows setting variables when assigning a value to a class field annotated with @ProcessVariableTyped or @ProcessVariable inside a method annotated with @StartProcess, as shown in the following example:

@Dependent
public class ProcessController {

  @ProcessVariable
  String myProcessVariable;

  @StartProcess("keyOfTheProcess")
  public void startProcessByKey() {
    myProcessVariable = "my-value";
  }

}

Since Quarkus tries to auto-inject beans into class fields annotated with @Qualifier annotations, the behavior, as shown above, doesn’t work out of the box. Instead, an exception is thrown.

However, if you know what you do and can spare the auto-inject behavior, it is possible to disable it. Read more about it in the ArC Configuration Reference.

Alternatively, you can set variables within a @StartProcess annotated method programmatically:

@Dependent
public class ProcessController {
  
  String myProcessVariable;

  @StartProcess("keyOfTheProcess")
  public void startProcessByKey() {
    myProcessVariable = "my-value";
    process.setVariable("myProcessVariable", myProcessVariable);
  }

}

@BusinessProcessScoped Beans

The camunda-engine-cdi-jakarta module stores @BusinessProcessScoped beans as process variables in the context of the current process instance.

Passivation is unsupported

Quarkus does not support Passivation and passivating scopes. When using @BusinessProcessScoped beans, no validation of being serializable and therefore “Passivation Capable” is performed during the startup of the Quarkus application.

If your @BusinessProcessScoped beans and their references don’t implement the java.io.Serializable interface, the engine throws an exception during execution when trying to persist the beans as process variables.

Destroying Bean Instances is unsupported

Programmatically destroying a @BusinessProcessScoped bean instance is currently unsupported.

The following API methods will throw an UnsupportedOperationException:

• javax.enterprise.inject.Instance#destroy
• io.quarkus.arc.InjectableContext#getState
• io.quarkus.arc.InjectableContext#destroy
• io.quarkus.arc.InjectableContext#destroy(Contextual<?> contextual)

Task form beans

Associating beans with Conversational Scope is currently not supported by Quarkus ArC. Furthermore, Quarkus does not allow to set a different default scope for beans that are outside of the extension’s control. As a result, the following conversational scoped beans are not available in a Quarkus application out of the box:

• org.camunda.bpm.engine.cdi.jsf.TaskForm
• org.camunda.bpm.engine.cdi.compat.FoxTaskForm
• org.camunda.bpm.engine.cdi.compat.CamundaTaskForm

In general, you can use these beans in custom JSF forms to interact with the process engine, for example, to render and complete user tasks. To include such functionality in your Quarkus application, provide custom beans with appropriate scopes and functionality. You can learn about the available beans and programming model in the CDI and Java EE Integration.