Obtaining matching events

import com.apama.jmon.*;

public class Simple implements Monitor, MatchListener {

   /**
   * No argument constructor used by the jmon framework on
   * application loading
   */
   public Simple() {}

   /**
   * Implementation of the Monitor interface onLoad method. Sets up
   * a single event expression looking for all stock trade events
   * with a trade price of greater than 10.0. This class instantiation
   * is added as a match listener to the event expression.
   */
   public void onLoad() {
     EventExpression eventExpr = new EventExpression("Tick(*, >10.0):t");
     eventExpr.addMatchListener(this);
   }

   /**
   * Implementation of the MatchListener interface match method.
   * Extracts the tick event that caused the event expression to
   * trigger and emits the event onto the default channel
   */
   public void match(MatchEvent event) {
     Tick tick = (Tick)event.getMatchingEvents().get("t");
    System.out.println("Event details: " + tick.name
       + " "   + tick.price);
     tick.emit();
   }
}

This specifies that when a suitable Tick event is detected, it must be recorded with the t tag. This allows a developer to get hold of the actual event that matched the event expression within the registered match listener’s match method.

Once the eventExpr listener detects a suitable event it will trigger and call match, passing to it a MatchEvent object. This object embeds within it all the individual event instances that together caused the event expression to be satisfied and were tagged.

In this example our event expression still consists of a single event template, and since this is tagged, then the MatchEvent object will contain the single Tick event that triggered the eventExpr listener. This will be tagged as t.