spring-servlet-pa-tomcat

Spring Servlet Process Application (using enbedded 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
• Uses a shared container managed process engine and Spring Beans as expression and delegate expression in the 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 managed container shared process engine paired with the power of spring beans inside your processes.

Show me the important parts!

We create a process application class which extends the ServletProcessApplication and annotate it with @ProcessApplication, so the camunda BPM platform can 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

There are couple important parts customized in this example:

1. all dependencies of web application itself are configured wit provided scope. As they are deployed into root classloader of web container

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

2. we prepare tomcat configuration, that is going to be used by container, by filtering variables in server.xml

```xml
<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">
```

3. we run embedded tomcat with our pre-configured server.xml

How to use it?

1. Build it with maven.

mvn clean verify

will start embedded tomcat using specified server.xml file, copy bpm-platform.xml into tomcat configuration folder.

2. Watch out for this console log:

[INFO] ENGINE-08046 Found camunda bpm platform configuration in
...
[INFO] ENGINE-07015 Detected @ProcessApplication class 'org.camunda.bpm.example.spring.servlet.pa.SpringServletProcessApplication'
Nov 30, 2016 10:43:33 AM 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