Implementing a Provider in Java

For ease of explanation, the process of implementing a provider in Java is explained using an example of a "Timer" provider that generates events at regular intervals and publishes a message to the Expresso server. The time interval and message are set in the properties file and can be changed by the user.

  1. Specifying data in the properties file. The configuration data that is required by the user can be specified in the pojoprovider.properties file. For this example, two properties are added:
    • expresso.providers.timer.interval.millsecs = 3000
    • expresso.providers.timer.message = Hello Expresso
  2. Implementing the POJO provider in Java. A provider can register itself with the Expresso server stating its name, description, and a list of events that it has to offer. The library offers two abstract classes that a user can extend to realise their provider and its events.
    Note: The project also needs the commons-configuration-1.10.jar and jetty-7 libraries in the build path.

Procedure

  1. Write a provider class that extends the AbstractExpressoProvider class.
  2. Define the class by mentioning its name and description by overriding the getName() and getDescription() methods.
  3. Return a list of events that the provider has by overriding the getProviderEvents() method.
  4. If required, write initialization code, such as loading data from the pojoprovider.properties file, in the overridden init() method.

Writing a Class that Extends the AbstractExpressoProvider Class

The following example illustrates the methods that the extending class must implement. The TimerProvider.java class extends the AbstractExpressoProvider class. 
import java.util.HashMap;
import java.util.Iterator;
import com.tibco.expresso.providers.api.AbstractExpressoEvent;
import com.tibco.expresso.providers.api.AbstractExpressoProvider;

public class TimerProvider extends AbstractExpressoProvider{
	
//These are user defined fields, specific to the provider

private static final String TIMER_PROPS = "expresso.providers.timer";
public static HashMap<String, String> timerData = new HashMap<String, String>();
public static final String TIMER_INTERVAL = "expresso.providers.timer.interval_ms";
public static final String TIMER_MESSAGE = "expresso.providers.timer.message"

@Override
public String getName() 
{
	// TODO Auto-generated method stub
	// name of the provider should be returned here

	return "Timer";
}
@Override
public String getDescription() 
{
	// TODO Auto-generated method stub
	// description of the provider should be returned here.

	return "Provides Timer events";
}

// The getProviderEvents() method will be explained and overridden 
//in later parts once we create events using the AbstractExpressoEvent 
//class as it returns a map of events that the provider has to offer.

@Override
public HashMap<String, AbstractExpressoEvent> getProviderEvents() 
{
	return null;
}

//This method can be used to initialize and load data specific to the 
//provider on its start up. All the properties mentioned in the 
//pojoprovider.properties file are available to the “config”  
//object of every provider and can be retrieved as shown below. 
//For this provider, we are saving them in timerData HashMap to 
//use later on.	

@Override
public void init() 
{

//Set the provider colour if required. 
//This colour will reflect in all the event pods specific to this 
//provider in the mobile app. The default value of colour is taken as 
//white if not set by the provider. 
 
  setProviderColour(Colour.Grey)

		Iterator<String> timerKeys = config.getKeys(TIMER_PROPS);
		while(timerKeys.hasNext()) 
		{
	         String key = timerKeys.next();
	         timerData.put(key, config.getString(key));
	   	}
		
	}
}