Package org.camunda.bpm.application.impl

Class ServletProcessApplication

  • All Implemented Interfaces:
    EventListener, javax.servlet.ServletContextListener, ProcessApplicationInterface
    Direct Known Subclasses:
    Application, InvoiceProcessApplication
    public class ServletProcessApplication
extends AbstractProcessApplication
implements javax.servlet.ServletContextListener

    A AbstractProcessApplication Implementation to be used in a Servlet container environment.

    This class implements the ServletContextListener interface and can thus participate in the deployment lifecycle of your web application.

    Usage

    In a Servlet 3.0 container it is sufficient adding a custom subclass of ServletProcessApplication annotated with @ProcessApplication to your application: 

     @ProcessApplication("Loan Approval App")
 public class LoanApprovalApplication extends ServletProcessApplication {
 // empty implementation
 }
    This, in combination with a META-INF/processes.xml file is sufficient for making sure that the process application class is picked up at runtime.

    In a Servlet 2.5 container, the process application can be added as a web listener to your project's web.xml

     <?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>

    Invocation Semantics

    When the AbstractProcessApplication.execute(java.util.concurrent.Callable) method is invoked, the servlet process application modifies the context classloader of the current Thread to the classloader that loaded the application-provided subclass of this class. This allows

    • the process engine to resolve JavaDelegate implementations using the classloader of the process application
    • In apache tomcat this allows you to resolve Naming Resources (JNDI) form the naming context of the process application. JNDI name resolution is based on the TCCL in Apache Tomcat.

                            Set TCCL of Process Application
                                     |
                                     |  +--------------------+
                                     |  |Process Application |
                       invoke        v  |                    |
      ProcessEngine -----------------O--|--> Java Delegate   |
                                        |                    |
                                        |                    |
                                        +--------------------+

    Process Application Reference

    The process engine holds a WeakReference to the ServletProcessApplication and does not cache any classes loaded using the Process Application classloader.

    Author:
    Daniel Meyer, Thorben Lindhauer