Using Monitoring

Using the monitoring framework in application code involves two steps, creating a monitor interface and injecting the monitor in a component.

Defining a Monitor Interface

The monitor interface is used for sending monitoring events. The interface defines operations for publishing events, monitoring levels and optional event message templates:

import org.fabric3.api.annotation.monitor.Severe;
import org.fabric3.api.annotation.monitor.Debug;

public inteface ComponentMonitor

   @Severe
   void error(String message, Throwable t);

   @Debug ("Received request {0}")
   void receivedRequest(String id);

}

The above interface defines an error event and a debug event. The debug event also specifies a formatted message that will be logged if the event is received. The following monitoring levels are supported:

• Severe - Critical errors that affect continue runtime operation
• Warning - Error conditions that do not affect continued runtime operation or a potential runtime configuration issue
• Info - Informational event
• Debug - An event useful for diagnosing a problem
• Trace - A low level event useful for diagnosing a problem

By default, Info and above are enabled at runtime.

Injecting the Monitor

A monitor is injected in a component using the org.fabric3.api.annotation.monitor.Monitor annotation:

import org.fabric3.api.annotation.monitor.Monitor;

public void TheComponent {

   @Monitor
   protected ComponentMonitor monitor;

   public void call(Message message) {
      monitor.receivedRequest(message.getId);
      try{
         validate(message));
      } catch (ValidationException e) {
         // bad message
         monitor.error("Invalid message", e)
      }

      // ...

   }

When an @Monitor annotation is encountered, the Fabric3 runtime will generate a monitor proxy and inject it based on the monitor interface. Depending on the current monitor level, events may be recorded or ignored. In the above example, if the monitor level is set to severe, the receivedRequest() event will be dropped.