Chapter 8. Decision engine event listeners and debug logging

In Red Hat Process Automation Manager, you can add or remove listeners for decision engine events, such as fact insertions and rule executions. With decision engine event listeners, you can be notified of decision engine activity and separate your logging and auditing work from the core of your application.

The decision engine supports the following default event listeners for the agenda and working memory:

  • AgendaEventListener
  • WorkingMemoryEventListener

For each event listener, the decision engine also supports the following specific events that you can specify to be monitored:

  • MatchCreatedEvent
  • MatchCancelledEvent
  • BeforeMatchFiredEvent
  • AfterMatchFiredEvent
  • AgendaGroupPushedEvent
  • AgendaGroupPoppedEvent
  • ObjectInsertEvent
  • ObjectDeletedEvent
  • ObjectUpdatedEvent
  • ProcessCompletedEvent
  • ProcessNodeLeftEvent
  • ProcessNodeTriggeredEvent
  • ProcessStartEvent

For example, the following code uses a DefaultAgendaEventListener listener attached to a KIE session and specifies the AfterMatchFiredEvent event to be monitored. The code prints pattern matches after the rules are executed (fired):

Example code to monitor and print AfterMatchFiredEvent events in the agenda

ksession.addEventListener( new DefaultAgendaEventListener() {
   public void afterMatchFired(AfterMatchFiredEvent event) {
       super.afterMatchFired( event );
       System.out.println( event );
   }
});

The decision engine also supports the following agenda and working memory event listeners for debug logging:

  • DebugAgendaEventListener
  • DebugRuleRuntimeEventListener

These event listeners implement the same supported event-listener methods and include a debug print statement by default. You can add a specific supported event to be monitored and documented, or monitor all agenda or working memory activity.

For example, the following code uses the DebugRuleRuntimeEventListener event listener to monitor and print all working memory events:

Example code to monitor and print all working memory events

ksession.addEventListener( new DebugRuleRuntimeEventListener() );

8.1. Configuring a logging utility in the decision engine

The decision engine uses the Java logging API SLF4J for system logging. You can use one of the following logging utilities with the decision engine to investigate decision engine activity, such as for troubleshooting or data gathering:

  • Logback
  • Apache Commons Logging
  • Apache Log4j
  • java.util.logging package

Procedure

For the logging utility that you want to use, add the relevant dependency to your Maven project or save the relevant XML configuration file in the org.drools package of your Red Hat Process Automation Manager distribution:

Example Maven dependency for Logback

<dependency>
  <groupId>ch.qos.logback</groupId>
  <artifactId>logback-classic</artifactId>
  <version>${logback.version}</version>
</dependency>

Example logback.xml configuration file in org.drools package

<configuration>
  <logger name="org.drools" level="debug"/>
  ...
<configuration>

Example log4j.xml configuration file in org.drools package

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
  <category name="org.drools">
    <priority value="debug" />
  </category>
  ...
</log4j:configuration>

Note

If you are developing for an ultra light environment, use the slf4j-nop or slf4j-simple logger.