Chapter 16. jBPM Process Definition Language (JPDL) - JBoss JBPM 3.1.3 userguide 英文版文档

Deploying process archives can be done in 3 ways: with the process designer tool, with an ant task or programatically.

Deploying a process archive with the designer tool is still under construction.

Deploying a process archive with an ant task can be done as follows:

<target name="deploy.par">
  <taskdef name="deploypar" classname="org.jbpm.ant.DeployParTask">
    <classpath --make sure the jbpm-[version].jar is in this classpath--/>  
  </taskdef>  
  <deploypar par="build/myprocess.par" /> 
</target>

To deploy more process archives at once, use the nested fileset elements. The file attribute itself is optional. Other attributes of the ant task are:

Process archives can also be deployed programmatically with the class org.jbpm.jpdl.par.ProcessArchiveDeployer

Process definitions should never change because it is extremely difficult (if not, impossible) to predict all possible side effects of process definition changes.

To get around this problem, jBPM has a sophicticated process versioning mechanism. The versioning mechanism allows multiple process definitions of the same name to coexist in the database. A process instance can be started in the latest version available at that time and it will keep on executing in that same process definition for its complete lifetime. When a newer version is deployed, newly created instances will be started in the newest version, while older process instances keep on executing in the older process defintions.

Process definitions are a combination of a declaratively specified process graph and optionally, a set of related java classes. The java classes can be made available to the jBPM runtime environment in 2 ways : by making sure these classes are visible to the jBPM classloader. This usually means that you can put your delegation classes in a .jar file next to the jbpm-[version].jar. The java classes can also be included in the process archive. When you include your delegation classes in the process archive (and they are not visible to the jbpm classloader), jBPM will also apply versioning on these classes. More information about process classloading can be found in Section 16.2, “Delegation”

When a process archive gets deployed, it creates a process definition in the jBPM database. Process definitions can be versioned on the basis of the process definition name. When a named process archive gets deployed, the deployer will assign a version number. To assign this number, the deployer will look up the highest version number for process definitions with the same name and adds 1. Unnamed process definitions will always have version number -1.

Changing process definitions after they are deployed into the jBPM database has many potential pitfalls. Therefor, this is highly discouraged.

Actually, there is a whole variety of possible changes that can be made to a process definition. Some of those process definitions are harmless, but some other changes have implications far beyond the expected and desirable.

So please consider migrating process instances to a new definition over this approach.

In case you would consider it, these are the points to take into consideration:

Use hibernate's update: You can just load a process definition, change it and save it with the hibernate session. The hibernate session can be accessed with the method JbpmContext.getSession().

The second level cache: A process definition would need to be removed from the second level cache after you've updated an existing process definition. See also Section 7.10, “Second level cache”

An alternative approach to changing process definitions might be to convert the executions to a new process definition. Please take into account that this is not trivial due to the long-lived nature of business processes. Currently, this is an experimental area so for which there are not yet much out-of-the-box support.

As you know there is a clear distinction between process definition data, process instance data (the runtime data) and the logging data. With this approach, you create a separate new process definition in the jBPM database (by e.g. deploying a new version of the same process). Then the runtime information is converted to the new process definition. This might involve a translation cause tokens in the old process might be pointing to nodes that have been removed in the new version. So only new data is created in the database. But one execution of a process is spread over two process instance objects. This might become a bit tricky for the tools and statistics calculations. When resources permit us, we are going to add support for this in the future. E.g. a pointer could be added from one process instance to it's predecessor.

A conversion class has been made available to assist you with converting your jBPM 2.0 process archives into jBPM 3.0 compatible process archives. Create an output directory to hold the converted process archives. Enter the following command line from the build directory of the jBPM 3.0 distribution:

java -jar converter.jar indirectory outdirectory

Substitute the input directory where your jBPM 2.0 process archives reside for "indirectory". Substitute the output directory for the one you created to hold the newly converted process archives for "outdirectory".

The jBPM class loader is the class loader that loads the jBPM classes. Meaning, the classloader that has the library jbpm-3.x.jar in its classpath. To make classes visible to the jBPM classloader, put them in a jar file and put the jar file besides the jbpm-3.x.jar. E.g. in the WEB-INF/lib folder in the case of webapplications.

Delegation classes are loaded with the process class loader of their respective process definition. The process class loader is a class loader that has the jBPM classloader as a parent. The process class loader adds all the classes of one particular process definition. You can add classes to a process definition by putting them in the /classes folder in the process archive. Note that this is only useful when you want to version the classes that you add to the process definition. If versioning is not necessary, it is much more efficient to make the classes available to the jBPM class loader.

Delegation classes contain user code that is called from within the execution of a process. The most common example is an action. In the case of action, an implementation of the interface ActionHandler can be called on an event in the process. Delegations are specified in the processdefinition.xml. 3 pieces of data can be supplied when specifying a delegation :

Next is a description of all the configuration types:

public class MyAction implements ActionHandler {
  // access specifiers can be private, default, protected or public
  private String city;
  Integer rounds;
  ...
}

...
<action class="org.test.MyAction">
  <city>Atlanta</city>
  <rounds>5</rounds>
</action>
...

When parsing a jPDL XML document, jBPM will validate your document against the jPDL schema when two conditions are met: first, the schema has to be referenced in the XML document like this

<process-definition xmlns="urn:jbpm.org:jpdl-3.1">
  ...
</process-definition>

And second, the xerces parser has to be on the classpath.

The jPDL schema can be found in ${jbpm.home}/src/java.jbpm/org/jbpm/jpdl/xml/jpdl-3.1.xsd or at http://jbpm.org/jpdl-3.1.xsd.