5.4. Running in KIE

5.4.1. KieRuntime

The KieRuntime provides methods that are applicable to both rules and processes, such as setting globals and registering channels. ("Exit point" is an obsolete synonym for "channel".)
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5.4.2. Globals in KIE

Globals are named objects that are made visible to the rule engine, but in a way that is fundamentally different from the one for facts: changes in the object backing a global do not trigger reevaluation of rules. Still, globals are useful for providing static information, as an object offering services that are used in the RHS of a rule, or as a means to return objects from the rule engine. When you use a global on the LHS of a rule, make sure it is immutable, or, at least, don't expect changes to have any effect on the behavior of your rules.
A global must be declared in a rules file, and then it needs to be backed up with a Java object. 
global java.util.List list
With the Knowledge Base now aware of the global identifier and its type, it is now possible to call ksession.setGlobal() with the global's name and an object, for any session, to associate the object with the global. Failure to declare the global type and identifier in DRL code will result in an exception being thrown from this call. 
List list = new ArrayList();
ksession.setGlobal("list", list);
Make sure to set any global before it is used in the evaluation of a rule. Failure to do so results in a NullPointerException.
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5.4.3. Event Packages

The event package provides means to be notified of rule engine events, including rules firing, objects being asserted, etc. This allows separation of logging and auditing activities from the main part of your application (and the rules).
The KieRuntimeEventManager interface is implemented by the KieRuntime which provides two interfaces, RuleRuntimeEventManager and ProcessEventManager. We will only cover the RuleRuntimeEventManager here.
The RuleRuntimeEventManager allows for listeners to be added and removed, so that events for the working memory and the agenda can be listened to.
The following code snippet shows how a simple agenda listener is declared and attached to a session. It will print matches after they have fired.

Example 5.14. Adding an AgendaEventListener

ksession.addEventListener( new DefaultAgendaEventListener() {
    public void afterMatchFired(AfterMatchFiredEvent event) {
        super.afterMatchFired( event );
        System.out.println( event );
    }
});
JBoss Rules also provides DebugRuleRuntimeEventListener and DebugAgendaEventListener which implement each method with a debug print statement. To print all Working Memory events, you add a listener like this:

Example 5.15. Adding a DebugRuleRuntimeEventListener

ksession.addEventListener( new DebugRuleRuntimeEventListener() );
All emitted events implement the KieRuntimeEvent interface which can be used to retrieve the actual KnowlegeRuntime the event originated from.
The events currently supported are:
  • MatchCreatedEvent
  • MatchCancelledEvent
  • BeforeMatchFiredEvent
  • AfterMatchFiredEvent
  • AgendaGroupPushedEvent
  • AgendaGroupPoppedEvent
  • ObjectInsertEvent
  • ObjectDeletedEvent
  • ObjectUpdatedEvent
  • ProcessCompletedEvent
  • ProcessNodeLeftEvent
  • ProcessNodeTriggeredEvent
  • ProcessStartEvent
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5.4.4. KieRuntimeLogger

The KieRuntimeLogger uses the comprehensive event system in JBoss Rules to create an audit log that can be used to log the execution of an application for later inspection, using tools such as the Eclipse audit viewer.

Example 5.16. FileLogger

KieRuntimeLogger logger = KieServices.Factory.get().getLoggers().newFileLogger( session, "audit" );  
...
// Be sure to close the logger otherwise it will not write.
logger.close();
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5.4.5. CommandExecutor Interface

KIE has the concept of stateful or stateless sessions. Stateful sessions have already been covered, which use the standard KieRuntime, and can be worked with iteratively over time. Stateless is a one-off execution of a KieRuntime with a provided data set. It may return some results, with the session being disposed at the end, prohibiting further iterative interactions. You can think of stateless as treating an engine like a function call with optional return results.
The foundation for this is the CommandExecutor interface, which both the stateful and stateless interfaces extend. This returns an ExecutionResults:
The CommandExecutor allows for commands to be executed on those sessions, the only difference being that the StatelessKieSession executes fireAllRules() at the end before disposing the session. The commands can be created using the CommandExecutor .The Javadocs provide the full list of the allowed comands using the CommandExecutor.
setGlobal and getGlobal are two commands relevant to JBoss Rules.
Set Global calls setGlobal underneath. The optional boolean indicates whether the command should return the global's value as part of the ExecutionResults. If true it uses the same name as the global name. A String can be used instead of the boolean, if an alternative name is desired.

Example 5.17. Set Global Command

StatelessKieSession ksession = kbase.newStatelessKieSession();
ExecutionResults bresults =
    ksession.execute( CommandFactory.newSetGlobal( "stilton", new Cheese( "stilton" ), true);
Cheese stilton = bresults.getValue( "stilton" );
Allows an existing global to be returned. The second optional String argument allows for an alternative return name.

Example 5.18. Get Global Command

StatelessKieSession ksession = kbase.newStatelessKieSession();
ExecutionResults bresults =
    ksession.execute( CommandFactory.getGlobal( "stilton" );
Cheese stilton = bresults.getValue( "stilton" );
All the above examples execute single commands. The BatchExecution represents a composite command, created from a list of commands. It will iterate over the list and execute each command in turn. This means you can insert some objects, start a process, call fireAllRules and execute a query, all in a single execute(...) call, which is quite powerful.
The StatelessKieSession will execute fireAllRules() automatically at the end. However the keen-eyed reader probably has already noticed the FireAllRules command and wondered how that works with a StatelessKieSession. The FireAllRules command is allowed, and using it will disable the automatic execution at the end; think of using it as a sort of manual override function.
Any command, in the batch, that has an out identifier set will add its results to the returned ExecutionResults instance.

Example 5.19. BatchExecution Command

StatelessKieSession ksession = kbase.newStatelessKieSession();

List cmds = new ArrayList();
cmds.add( CommandFactory.newInsertObject( new Cheese( "stilton", 1), "stilton") );
cmds.add( CommandFactory.newStartProcess( "process cheeses" ) );
cmds.add( CommandFactory.newQuery( "cheeses" ) );
ExecutionResults bresults = ksession.execute( CommandFactory.newBatchExecution( cmds ) );
Cheese stilton = ( Cheese ) bresults.getValue( "stilton" );
QueryResults qresults = ( QueryResults ) bresults.getValue( "cheeses" );
In the above example multiple commands are executed, two of which populate the ExecutionResults. The query command defaults to use the same identifier as the query name, but it can also be mapped to a different identifier.
All commands support XML and jSON marshalling using XStream, as well as JAXB marshalling. This is covered in the Rule Commands section: Section 8.1, “Available API”.
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