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3.6. Actions

You can use actions in these ways:
  • within an Action node,
  • as entries or exits, (with a number of nodes),
  • to specify the the behavior of exception handlers.
Actions have access to globals and those variables that are defined for the process and the predefined context variable. This latter is of the type org.drools.runtime.process.ProcessContext and can be used for the following tasks:
  • obtaining the current node instance. The node instance can be queried for such information as its name and type. You can also cancel it: 
    NodeInstance node = context.getNodeInstance();
String name = node.getNodeName();
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  • obtaining the current process instance. A process instance can be queried for such information as its name and processId. It can also be aborted or signalled via an internal event: 
    WorkflowProcessInstance proc = context.getProcessInstance();
proc.signalEvent( type, eventObject );
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  • obtaining or setting the value of variables.
  • accessing the knowledge run-time, in order to do things like start a process, signal external events or insert data.
Java actions should be valid Java code.
MVEL actions can use this business scripting language to express the action. MVEL accepts any valid Java code but also provides support for nested accesses of parameters (such as, person.name instead of person.getName()), and various other advantages. Thus, MVEL expressions are normally more convenient for the business user. For example, an action that prints out the name of the person in the rule flow's requester variable will: look like this: 
// Java dialect
System.out.println( person.getName() );

//  MVEL dialect
System.out.println( person.name );
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