JavaServices

Using Services in Java - Example 7

This example is a reimplementation of example 4 in Java. There's really not much to say here, as in the previous example the code is very similar to the code in the C++ version (with the minor exception of protobuf usage).

The Service Provider (BasicServiceProvider)

For the provider, we first set up the request listener:

class MultiplicationServiceProvider implements GravityServiceProvider
{
	public  MultiplicationServiceProvider()
	{
	}

	@Override
	public GravityDataProduct request(String serviceID, GravityDataProduct dataProduct)
	{
		//Just to be safe.  In theory this can never happen unless this class is registered with more than one serviceID types.
		if(!dataProduct.getDataProductID().equals("Multiplication")) {
			Log.critical(String.format("Request is not for %s, not Multiplication!", dataProduct.getDataProductID()));
			return new GravityDataProduct("BadRequest");
		}

		//Get the parameters for this request.
		Multiplication.MultiplicationOperandsPB.Builder params = Multiplication.MultiplicationOperandsPB.newBuilder();
		dataProduct.populateMessage(params);

		Log.warning(String.format("%d x %d", params.getMultiplicandA(), params.getMultiplicandB()));

		//Do the calculation
		int result = params.getMultiplicandA() * params.getMultiplicandB();

		//Return the results to the requestor
		Multiplication.MultiplicationResultPB.Builder resultPB = Multiplication.MultiplicationResultPB.newBuilder();
		resultPB.setResult(result);

		GravityDataProduct resultDP = new GravityDataProduct("MultiplicationResult");
		resultDP.setData(resultPB);

		return resultDP;
	}
}

Once that's done, we can register it:

	MultiplicationServiceProvider msp = new MultiplicationServiceProvider();
	gn.registerService(
			//This identifies the Service to the service directory so that others can
			// make a request to it.
			"Multiplication",
			//Assign a transport type to the socket (almost always tcp, unless you are only
			//using the gravity data product between two processes on the same computer).
			GravityTransportType.TCP,
			//Give an instance of the multiplication service class to be called when a request is made for multiplication.
			msp);

The Requester (BasicServiceRequestor)

And for the requester, we setup the response listener:

//After multiplication is requested, this class may be called with the result.  
class MultiplicationRequestor implements GravityRequestor
{
	public void requestFilled(String serviceID, String requestID, GravityDataProduct response)
	{
		//Parse the message into a protobuf.  
		Multiplication.MultiplicationResultPB.Builder result = Multiplication.MultiplicationResultPB.newBuilder();
		response.populateMessage(result);
		
		//Write the answer
		Log.message(String.format("%s: %d", requestID, result.getResult()));
		
		gotAsyncMessage = true;
	}

	boolean gotAsyncMessage = false;
	public boolean gotMessage() { return gotAsyncMessage; }
}

And then we make the asynchronous request that uses the listener:

	/////////////////////////////
	// Set up the first multiplication request
	MultiplicationRequestor requestor = new MultiplicationRequestor();
	
	GravityDataProduct multRequest1 = new GravityDataProduct("Multiplication");
	Multiplication.MultiplicationOperandsPB.Builder params1 = Multiplication.MultiplicationOperandsPB.newBuilder();
	params1.setMultiplicandA(8);
	params1.setMultiplicandB(2);
	multRequest1.setData(params1);
	
	// Make an Asynchronous request for multiplication
	do {
		ret = gn.request("Multiplication", //Service Name
				 multRequest1, //Request
				 requestor, //Object containing callback that will get the result.
				 "8 x 2"); //A string that identifies which request this is.
		// Service may not be registered yet
		if (ret != GravityReturnCode.SUCCESS)
		{
			Log.warning("Failed request to Multiplication, retrying...");
			Thread.sleep(1000);
		}
	} while (ret != GravityReturnCode.SUCCESS);

And lastly, we make the synchronous request against the same service:

	/////////////////////////////////////////
	//Set up the second multiplication request
	GravityDataProduct multRequest2 = new GravityDataProduct("Multiplication");
	Multiplication.MultiplicationOperandsPB.Builder params2 = Multiplication.MultiplicationOperandsPB.newBuilder();
	params2.setMultiplicandA(5);
	params2.setMultiplicandB(7);
	multRequest2.setData(params2);

	//Make a Synchronous request for multiplication
	GravityDataProduct multSync = gn.request("Multiplication", //Service Name
							multRequest2, //Request
							1000); //Timeout in milliseconds

	if(multSync == null)
	{
		Log.critical("Request Returned NULL!");
	}
	else
	{
		Multiplication.MultiplicationResultPB.Builder result = Multiplication.MultiplicationResultPB.newBuilder();
		multSync.populateMessage(result);
		
		Log.message(String.format("5 x 7 = %d", result.getResult()));
	}