Passing Events Between Monitors (Routing)

In this lesson, you update your program so that the SensorMonitor creates new derived events from the incoming events and routes these derived events (Alerts) to a new monitor called AlertManager for further handling.

Add an event definition

You must define any event that you want the correlator to process - whether the event originates from an external source or is routed internally by your EPL program.

Your program will generate an alert message (output event) if it encounters temperature or pressure values that exceed normal parameters.

Follow these steps to define an event type definition for these Alert events:

1. Open the eventdefinitions/SensorMonitorEvents.mon file.

2. Add an event definition for the Alert event type with the following fields, in the following order:

   • type (string)
   • sensorId (string)
   • temperature (float)
   • pressure (float)
   
   
   Info

   The type field is a textual description of the alert condition. The sensorId is a unique identifier for the sensors in the fictional industrial process. The fields Temperature and Pressure identify the temperature in celsius and the pressure in kilopascals.

3. Save your changes.

Route an event

To edit the SensorMonitor to route Alert events:

1. Open the SensorMonitor.mon file.

2. Change the print statement to route statement as follows:

   Change:

   print "TEMP_PRESSURE_RISE: " + temperature.toString() + " " + pressure.toString();
   

   To:

   route Alert("TEMP_PRESSURE_RISE", sensorId, temperature.temperature, pressure.pressure);  
   

3. Save the file.

Create a monitor to listen for the routed event

Create a new monitor, in a separate file, that listens and acts on the Alert events:

1. Right-click on the monitors folder and select new file.

2. Enter AlertManager.mon for the file name.

3. Edit the generated monitor as below so that it listens for the routed Alert event and prints it:

   monitor AlertManager {  
       action onload () {  
           on all Alert() as a {  
               print a.toString();  
           }  
       }  
   }  
   

4. Save your changes.

5. Run the project, making sure to also inject the new monitor you have created. You should see Alert messages for the S001 and S003 sensors.

You can import the completed solution for this lesson:

In the Apama Samples Git repository, navigate to the tutorials/EPL_Fundamentals_Completed directory.