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:

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

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):

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:

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:

ksession.addEventListener( new DebugRuleRuntimeEventListener() );

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

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

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