spring-servlet-pa-tomcat

Spring Servlet Process Application (using embedded Tomcat 7)

This example demonstrates how to deploy a spring powered web application which

• Includes a @ProcessApplication class and some BPMN 2.0 processes
• Starts a Spring Web application context based on a shared, container managed process engine
• Uses Spring Beans and delegation code in expressions within processes

Why is this example interesting?

This example shows how to combine a @ProcessApplication class, a processes.xml and a spring applicationContext into a fully-fledged process application with all its advantages, including a shared, container managed process engine paired with the power of Spring Beans inside your processes.

Show me the important parts!

A process application class was created which extends the ServletProcessApplication class. The class was annotated with @ProcessApplication. This allows the Camunda Platform to pick it up and register the process application without any further action:

@ProcessApplication
public class SpringServletProcessApplication extends ServletProcessApplication {
  ...
}

Through the META-INF/processes.xml, we can define process archives and additional options, like creating new engines when deploying the process application:

<?xml version="1.0" encoding="UTF-8"?>
<process-application
  xmlns="http://www.camunda.org/schema/1.0/ProcessApplication"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.camunda.org/schema/1.0/ProcessApplication http://www.camunda.org/schema/1.0/ProcessApplication">

  <process-archive>
  <properties>
    <property name="isDeleteUponUndeploy">true</property>
  </properties>
  
  </process-archive>

</process-application>

Maven dependencies

The scope attributes of the dependency nodes are set to provided since the dependencies have to be loaded into the root classloader of the web container:

<dependency>
  <groupId>org.camunda.bpm</groupId>
  <artifactId>camunda-engine-spring</artifactId>
  <version>${camunda.version}</version>
  <scope>provided</scope>
</dependency>

The embedded tomcat server will be run with our pre-configured server.xml. This configuration file will be preprocessed so that variables with the name ${project.build.directory} are being replaced with the proper path:

<Resource 
  name="jdbc/ProcessEngine"
  auth="Container"
  type="javax.sql.DataSource"
  factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
  uniqueResourceName="process-engine"
  driverClassName="org.h2.Driver"
  url="jdbc:h2:${project.build.directory}/camunda-h2-dbs/process-engine;MVCC=TRUE;TRACE_LEVEL_FILE=0;DB_CLOSE_ON_EXIT=FALSE"
  username="sa"
  password="sa"
  maxPoolSize="20"
  minPoolSize="5" />
...
<Host name="localhost"  appBase="${project.build.directory}/to_deploy"
  unpackWARs="true" autoDeploy="true">

The configuration files server.xml and bpm-platform.xml are being copied to the respective tomcat configuration path.

How to use it?

1. Build it with Maven.

mvn clean verify

This will start the embedded tomcat server.

2. Watch out for this console log:

[INFO] ENGINE-08046 Found Camunda Platform configuration in
...
[INFO] ENGINE-07015 Detected @ProcessApplication class 'org.camunda.bpm.example.spring.servlet.pa.SpringServletProcessApplication'
May 18, 2020 4:46:36 PM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring root WebApplicationContext
...
Invoking @PostDeploy annotation in org.camunda.bpm.example.spring.servlet.pa.SpringServletProcessApplication
Starting testResolveBean processdefinition
org.camunda.bpm.example.spring.servlet.pa.ExampleBean is currently invoked.
Starting testResolveBeanFromJobExecutor processdefinition