The Process Application class

You can delegate the bootstrapping of the process engine and process deployment to a process application class. The basic ProcessApplication functionality is provided by the org.camunda.bpm.application.AbstractProcessApplication base class. Based on this class there is a set of environment-specific sub classes that realize integration within a specific environment:

  • ServletProcessApplication: To be used for Process Applications in a Servlet Container like Apache Tomcat.
  • EjbProcessApplication: To be used in a Java EE application server like JBoss, Glassfish or IBM WebSphere Application Server.
  • EmbeddedProcessApplication: To be used when embedding the process engine in an ordinary Java SE application.
  • SpringProcessApplication: To be used for bootstrapping the process application from a Spring Application Context.

In the following section, we walk through the different implementations and discuss where and how they can be used.

The ServletProcessApplication

Supported on: Apache Tomcat, JBoss/Wildfly, GlassFish. The Servlet Process Application is supported on all containers. Read the note about Servlet Process Application and EJB/Java EE containers

Packaging: WAR (or embedded WAR inside EAR)

The ServletProcessApplication class is the base class for developing Process Applications based on the Servlet Specification (Java Web Applications). The servlet process application implements the javax.servlet.ServletContextListener interface which allows it to participate in the deployment lifecycle of your Web application

The following is an example of a Servlet Process Application:

package org.camunda.bpm.example.loanapproval;

import org.camunda.bpm.application.ProcessApplication;
import org.camunda.bpm.application.impl.ServletProcessApplication;

@ProcessApplication("Loan Approval App")
public class LoanApprovalApplication extends ServletProcessApplication {
  // empty implementation
}

Notice the @ProcessApplication annotation. This annotation fulfills two purposes:

  • providing the name of the ProcessApplication: You can provide a custom name for your process application using the annotation: @ProcessApplication("Loan Approval App"). If no name is provided, a name is automatically detected. In case of a ServletProcessApplication, the name of the ServletContext is used.
  • triggering auto-deployment. In a Servlet 3.0 container, the annotation is sufficient for making sure that the process application is automatically picked up by the servlet container and automatically added as a ServletContextListener to the Servlet Container deployment. This functionality is realized by a javax.servlet.ServletContainerInitializer implementation named org.camunda.bpm.application.impl.ServletProcessApplicationDeployer which is located in the camunda-engine module. The implementation works for both embedded deployment of the camunda-engine.jar as a web application library in the WEB-INF/lib folder of your WAR file or for the deployment of the camunda-engine.jar as a shared library in the shared library (e.g. Apache Tomcat global lib/ folder) directory of your application server. The Servlet 3.0 Specification foresees both deployment scenarios. In case of embedded deployment, the ServletProcessApplicationDeployer is notified once, when the webapplication is deployed. In case of deployment as a shared library, the ServletProcessApplicationDeployer is notified for each WAR file containing a class annotated with @ProcessApplication (as required by the Servlet 3.0 Specification).

This means that in case you deploy to a Servlet 3.0 compliant container (such as Apache Tomcat 7) annotating your class with @ProcessApplication is sufficient.

There is a project template for Maven called camunda-archetype-servlet-war, which gives you a complete running project based on a ServletProcessApplication.

Deploying to Apache Tomcat 6 or Other Pre-Servlet 3.0 Containers

In a Pre-Servlet 3.0 container such as Apache Tomcat 6 (or JBoss Application Server 5 for that matter), you need manually register your ProcessApplication class as Servlet Context Listener in the Servlet Container. This can be achieved by adding a listener element to your WEB-INF/web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <listener>
    <listener-class>org.my.project.MyProcessApplication</listener-class>
  </listener>

</web-app>

Using the ServletProcessApplication Inside an EJB/Java EE Container such as Glassfish or JBoss

You can use the ServletProcessApplication inside an EJB / Java EE Container such as Glassfish or JBoss. Process application bootstrapping and deployment will work in the same way. However, you will not be able to use all Java EE features at runtime. In contrast to the EjbProcessApplication (see next section), the ServletProcessApplication does not perform proper Java EE cross-application context switching. When the process engine invokes Java Delegates from your application, only the Context Class Loader of the current Thread is set to the classloader of your application. This does allow the process engine to resolve Java Delegate implementations from your application but the container will not perform an EE context switch to your application. As a consequence, if you use the ServletProcessApplciation inside a Java EE container, you will not be able to use features like:

  • using CDI beans and EJBs as JavaDelegate Implementations in combination with the Job Executor,
  • using @RequestScoped CDI Beans with the Job Executor,
  • looking up JNDI resources from the application’s naming scope

If your application does not use such features, it is perfectly fine to use the ServletProcessApplication inside an EE container. In that case you only get servlet specification guarantees.

The EjbProcessApplication

Supported on: JBoss/Wildfly, GlassFish. The EjbProcessApplication is supported on Java EE 6 containers or higher. It is not supported on Servlet Containers like Apache Tomcat. It may be adapted to work inside Java EE 5 Containers.

Packaging: JAR, WAR, EAR

The EjbProcessApplication is the base class for developing Java EE based Process Applications. An Ejb Process Application class itself must be deployed as an EJB.

In order to add an Ejb Process Application to your Java Application, you have two options:

  • Bundling the camunda-ejb-client: we provide a generic, reusable EjbProcessApplication implementation (named org.camunda.bpm.application.impl.ejb.DefaultEjbProcessApplication) bundled as a maven artifact. The simplest possibility is to add this implementation as a maven dependency to your application.
  • Writing a custom EjbProcessApplication: if you want to customize the behavior of the EjbProcessApplication, you can write a custom subclass of the EjbProcessApplication class and add it to your application.

Both options are explained in greater detail below.

Bundling the camunda-ejb-client Jar

The most convenient option for deploying a process application to an Ejb Container is by adding the following maven dependency to you maven project:

Please import the Camunda BOM to ensure correct versions for every Camunda project.

<dependency>
  <groupId>org.camunda.bpm.javaee</groupId>
  <artifactId>camunda-ejb-client</artifactId>
</dependency>

The camunda-ejb-client contains a reusable default implementation of the EjbProcessApplication as a Singleton Session Bean with auto-activation.

This deployment option requires that your project is a composite deployment (such as a WAR or EAR) since you need to add a library JAR file. You could of course use something like the maven shade plugin for adding the class contained in the camunda-ejb-client artifact to a JAR-based deployment.

We always recommend using the camunda-ejb-client over deploying a custom EjbProcessApplication class unless you want to customize the behavior of the EjbProcessApplication.

There is a project template for Maven called camunda-archetype-servlet-war, which gives you a complete running project based on a ServletProcessApplication.

Deploying a Custom EjbProcessApplication Class

If you want to customize the behavior of the the EjbProcessApplication class you have the option of writing a custom EjbProcessApplication class. The following is an example of such an implementation:

@Singleton
@Startup
@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
@TransactionAttribute(TransactionAttributeType.REQUIRED)
@ProcessApplication
@Local(ProcessApplicationInterface.class)
public class MyEjbProcessApplication extends EjbProcessApplication {

  @PostConstruct
  public void start() {
    deploy();
  }

  @PreDestroy
  public void stop() {
    undeploy();
  }

}

Expose Servlet Context Path Using a Custom EjbProcessApplication

If your application is a WAR (or a WAR inside an EAR) and you want to use embedded forms or external task forms inside the Tasklist application, then your custom EjbProcessApplication must expose the servlet context path of your application as a property. This enables the Tasklist to resolve the path to the embedded or external task forms.

Therefore your custom EjbProcessApplication must be extended by a Map and a getter-method for that Map as follows:

@Singleton
@Startup
@ConcurrencyManagement(ConcurrencyManagementType.BEAN)
@TransactionAttribute(TransactionAttributeType.REQUIRED)
@ProcessApplication
@Local(ProcessApplicationInterface.class)
public class MyEjbProcessApplication extends EjbProcessApplication {

  protected Map<String, String> properties = new HashMap<String, String>();

  @PostConstruct
  public void start() {
    deploy();
  }

  @PreDestroy
  public void stop() {
    undeploy();
  }

  public Map<String, String> getProperties() {
    return properties;
  }

}

Furthermore, to provide the servlet context path a custom javax.servlet.ServletContextListener must be added to your application. Inside your custom implementation of the ServletContextListener you have to

  • inject your custom EjbProcessApplication using the @EJB annotation,
  • resolve the servlet context path and
  • expose the servlet context path through the ProcessApplicationInfo#PROP_SERVLET_CONTEXT_PATH property inside your custom EjbProcessApplication.

This can be done as follows:

public class ProcessArchiveServletContextListener implements ServletContextListener {

  @EJB
  private ProcessApplicationInterface processApplication;

  public void contextInitialized(ServletContextEvent contextEvent) {

    String contextPath = contextEvent.getServletContext().getContextPath();

    Map<String, String> properties = processApplication.getProperties();
    properties.put(ProcessApplicationInfo.PROP_SERVLET_CONTEXT_PATH, contextPath);
  }

  public void contextDestroyed(ServletContextEvent arg0) {
  }

}

Finally the custom ProcessArchiveServletContextListener has to be added to your WEB-INF/web.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <listener>
    <listener-class>org.my.project.ProcessArchiveServletContextListener</listener-class>
  </listener>

  ...

</web-app>

Invocation Semantics of the EjbProcessApplication

The fact that the EjbProcessApplication exposes itself as a Session Bean Component inside the EJB container determines

  • the invocation semantics when invoking code from the process application and
  • the nature of the ProcessApplicationReference held by the process engine.

When the process engine invokes the Ejb Process Application, it gets EJB invocation semantics. For example, if your process application provides a JavaDelegate implementation, the process engine will call the EjbProcessApplication’s execute(Callable) method and from that method invoke the JavaDelegate. This makes sure that

  • the call is intercepted by the EJB container and “enters” the process application legally.
  • the JavaDelegate may take advantage of the EjbProcessApplication’s invocation context and resolve resources from the component’s environment (such as a java:comp/BeanManager).
                   Big pile of EJB interceptors
                                |
                                |  +--------------------+
                                |  |Process Application |
                  invoke        v  |                    |
 ProcessEngine ----------------OOOOO--> Java Delegate   |
                                   |                    |
                                   |                    |
                                   +--------------------+

The EjbProcessApplication allows to hook into the invocation by overriding the execute(Callable callable, InvocationContext invocationContext) method. It provides the context of the current invocation (e.g. the execution) and can be used to execute custom code, for example initialize the security context before a service task is invoked.

public class MyEjbProcessApplication extends EjbProcessApplication {

  @Override
  public <T> T execute(Callable<T> callable, InvocationContext invocationContext) {
    
    if(invocationContext != null) {
      // execute custom code (e.g. initialize the security context)
    }
    
    return execute(callable);
  }
}

When the EjbProcessApplication registers with a process engine (see ManagementService#registerProcessApplication(String, ProcessApplicationReference), the process application passes a reference to itself to the process engine. This reference allows the process engine to reference the process application. The EjbProcessApplication takes advantage of the Ejb Containers naming context and passes a reference containing the EJBProcessApplication’s Component Name to the process engine. Whenever the process engine needs access to process application, the actual component instance is looked up and invoked.

The EmbeddedProcessApplication

Supported on: JVM, Apache Tomcat, JBoss/Wildfly, GlassFish

Packaging: JAR, WAR, EAR

The org.camunda.bpm.application.impl.EmbeddedProcessApplication can only be used in combination with an embedded process engine. Usage in combination with a Shared Process Engine is not supported as the class performs no process application context switching at runtime.

The Embedded Process Application also does not provide auto-startup. You need to manually call the deploy method of your process application:

// instantiate the process application
MyProcessApplication processApplication = new MyProcessApplication();

// deploy the process application
processApplication.deploy();

// interact with the process engine
ProcessEngine processEngine = BpmPlatform.getDefaultProcessEngine();
processEngine.getRuntimeService().startProcessInstanceByKey(...);

// undeploy the process application
processApplication.undeploy();

Where the class MyProcessApplication could look like this:

@ProcessApplication(
    name="my-app",
    deploymentDescriptors={"path/to/my/processes.xml"}
)
public class MyProcessApplication extends EmbeddedProcessApplication {

}

Remember that to make a manually managed EmbeddedProcessApplication work, you will have to register your ProcessEngine on the RuntimContainer:

RuntimeContainerDelegate runtimeContainerDelegate = RuntimeContainerDelegate.INSTANCE.get();
runtimeContainerDelegate.registerProcessEngine(processEngine);

The SpringProcessApplication

Supported on: JVM, Apache Tomcat, GlassFish. The spring process application is currently not supported on JBoss AS 7/Wildfly 8

Packaging: JAR, WAR, EAR

The org.camunda.bpm.engine.spring.application.SpringProcessApplication class allows bootstrapping a process application through a Spring Application Context. You can either reference the SpringProcessApplication class from an XML-based application context configuration file or use an annotation-based setup.

If your application is a WebApplication you should use org.camunda.bpm.engine.spring.application.SpringServletProcessApplication as it provides support for exposing the servlet context path through the ProcessApplicationInfo#PROP_SERVLET_CONTEXT_PATH property.

We recommend to always use SpringServletProcessApplication unless the deployment is not a web application. Using this class requires the org.springframework:spring-web module to be on the classpath.

Configuring a Spring Process Application

The following shows an example of how to bootstrap a SpringProcessApplication inside a spring application context XML file:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd">

  <bean id="invoicePa" class="org.camunda.bpm.engine.spring.application.SpringServletProcessApplication" />

</beans>

(Remember that you additionally need a META-INF/processes.xml file.

If you are manually managing your processEngine, you will have to register it on the RuntimeContainerDelegate as described in the EmbeddedProcessEngine section.

Process Application Name

The SpringProcessApplication will use the bean name (id="invoicePa" in the example above) as auto-detected name for the process application. Make sure to provide a unique process application name here (unique across all process applications deployed on a single application server instance.) As an alternative, you can provide a custom subclass of SpringProcessApplication (or SpringServletProcessApplication) and override the getName() method.

Configure a Managed Process Engine Using Spring

If you use a Spring Process Application, you may want to configure your process engine inside the spring application context Xml file (as opposed to the processes.xml file). In this case, you must use the org.camunda.bpm.engine.spring.container.ManagedProcessEngineFactoryBean class for creating the process engine object instance. In addition to creating the process engine object, this implementation registers the process engine with the BPM Platform infrastructure so that the process engine is returned by the ProcessEngineService. The following is an example of how to configure a managed process engine using Spring.

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
                           http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="dataSource" class="org.springframework.jdbc.datasource.TransactionAwareDataSourceProxy">
        <property name="targetDataSource">
            <bean class="org.springframework.jdbc.datasource.SimpleDriverDataSource">
                <property name="driverClass" value="org.h2.Driver"/>
                <property name="url" value="jdbc:h2:mem:camunda;DB_CLOSE_DELAY=1000"/>
                <property name="username" value="sa"/>
                <property name="password" value=""/>
            </bean>
        </property>
    </bean>

    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <bean id="processEngineConfiguration" class="org.camunda.bpm.engine.spring.SpringProcessEngineConfiguration">
        <property name="processEngineName" value="default" />
        <property name="dataSource" ref="dataSource"/>
        <property name="transactionManager" ref="transactionManager"/>
        <property name="databaseSchemaUpdate" value="true"/>
        <property name="jobExecutorActivate" value="false"/>
    </bean>

    <!-- using ManagedProcessEngineFactoryBean allows registering the ProcessEngine with the BpmPlatform -->
    <bean id="processEngine" class="org.camunda.bpm.engine.spring.container.ManagedProcessEngineFactoryBean">
        <property name="processEngineConfiguration" ref="processEngineConfiguration"/>
    </bean>

    <bean id="repositoryService" factory-bean="processEngine" factory-method="getRepositoryService"/>
    <bean id="runtimeService" factory-bean="processEngine" factory-method="getRuntimeService"/>
    <bean id="taskService" factory-bean="processEngine" factory-method="getTaskService"/>
    <bean id="historyService" factory-bean="processEngine" factory-method="getHistoryService"/>
    <bean id="managementService" factory-bean="processEngine" factory-method="getManagementService"/>

</beans>

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