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3.7. Data

Throughout the execution of a process, data can be retrieved, stored, passed on, and used. To store runtime data during the execution of the process, process variables are used. A variable is defined with a name and a data type. A basic data type could include the following: boolean, int, String, or any kind of object subclass.
Variables can be defined inside a variable scope. The top-level scope is the variable scope of the process itself. Sub-scopes can be defined using a sub-process. Variables that are defined in a sub-scope are only accessible for nodes within that scope.
Whenever a variable is accessed, the process will search for the appropriate variable scope that defines the variable. Nesting variable scopes are allowed. A node will always search for a variable in its parent container; if the variable cannot be found, the node will look in the parent's parent container, and so on, until the process instance itself is reached. If the variable cannot be found, a read access yields null, and a write access produces an error message. All of this occurs with the process continuing execution.
Variables can be used in the following ways:
  • Process-level variables can be set when starting a process by providing a map of parameters to the invocation of the startProcess method. These parameters will be set as variables on the process scope.
  • Script actions can access variables directly simply by using the name of the variable as a local parameter in their script. For example, if the process defines a variable of type "org.jbpm.Person" in the process, a script in the process could access this directly:
    // call method on the process variable "person"
    
    person.setAge(10);
    Changing the value of a variable in a script can be done through the knowledge context:
    kcontext.setVariable(variableName, value);
  • Service tasks (and reusable sub-processes) can pass the value of process variables to the outside world (or another process instance) by mapping the variable to an outgoing parameter. For example, the parameter mapping of a service task could define that the value of the process variable x should be mapped to a task parameter y just before the service is invoked. You can also inject the value of the process variable into a hard-coded parameter String using #{expression}. For example, the description of a human task could be defined as the following:
    You need to contact person #{person.getName()}
    
    Where person is a process variable. This will replace this expression with the actual name of the person when the service needs to be invoked. Similarl results of a service (or reusable sub-process) can also be copied back to a variable using result mapping.
  • Various other nodes can also access data. Event nodes, for example, can store the data associated to the event in a variable. Check the properties of the different node types for more information.
Finally, processes (and rules) have access to globals, i.e., globally defined variables and data in the Knowledge Session. Globals are directly accessible in actions like variables. Globals need to be defined as part of the process before they can be used. Globals can be set using the following:
ksession.setGlobal(name, value)
Globals can also be set from inside process scripts using:
kcontext.getKnowledgeRuntime().setGlobal(name,value);.