Getting message from the server using RPC( Remote Procedure Call )

This examples describes the procedure of retrieving message from the server via RPC. The steps involved in geting message from the server are described below:-

Step1:-Right-click on the GWT project node which you have created and choose New > Other. In the New File wizard, click on the Google Web Toolkit category shows a file template named GWT RPC Service. Click Next.
Step2:- Fill the sub package box, the name of the package where the files that will be generated will be stored.
Step3:-Click Finish. The Projects window will automatically updates to reflect changes
Step4:- Create the following Classes.

GWTService.java:- This is the client-side definition of the service.


package org.yournamehere.client;

import com.google.gwt.user.client.rpc.RemoteService;

public interface GWTService extends RemoteService{

    public String myMethod(String s);

}

GWTServiceAsync.java:-This is the client side definition. It provides a callback object that enables the asynchronous communication between server and client.


package org.yournamehere.client;

import com.google.gwt.user.client.rpc.AsyncCallback;



public interface GWTServiceAsync {

    public void myMethod(String s, AsyncCallback callback);

}

GWTServiceImpl.java:-This is the servlet that implements the interface. it provides the functionality for retrieving a quote via RPC.


package org.yournamehere.server;

import com.google.gwt.user.server.rpc.RemoteServiceServlet;

import org.yournamehere.client.GWTService;



public class GWTServiceImpl extends RemoteServiceServlet implements

    GWTService {



    public String myMethod(String s) {

        return "Server says: " + s;

    }

}

GWTServiceUsageExample.java:-This is the interface that will instantiates the service.




package org.yournamehere.client;



import com.google.gwt.core.client.GWT;

import com.google.gwt.user.client.rpc.AsyncCallback;

import com.google.gwt.user.client.rpc.ServiceDefTarget;

import com.google.gwt.user.client.ui.Button;

import com.google.gwt.user.client.ui.ClickListener;

import com.google.gwt.user.client.ui.Label;

import com.google.gwt.user.client.ui.TextBox;

import com.google.gwt.user.client.ui.VerticalPanel;

import com.google.gwt.user.client.ui.Widget;



public class GWTServiceUsageExample extends VerticalPanel {

    private Label lblServerReply = new Label();

    private TextBox txtUserInput = new TextBox();

    private Button btnSend = new Button("Send to server");

    

    public GWTServiceUsageExample() {

        add(new Label("Input your text: "));

        add(txtUserInput);

        add(btnSend);

        add(lblServerReply);



        final AsyncCallback callback = new AsyncCallback() {

            public void onSuccess(Object result) {

                lblServerReply.setText((String)result);

            }

            

            public void onFailure(Throwable caught) {

                lblServerReply.setText("Communication failed");

            }

        };

        

          btnSend.addClickListener(new ClickListener(){

            public void onClick(Widget w) {

                       getService().myMethod(txtUserInput.getText(), callback);

            }

        });

    }

    

    public static GWTServiceAsync getService(){

       

        GWTServiceAsync service = (GWTServiceAsync) GWT.create(GWTService.class);

        ServiceDefTarget endpoint = (ServiceDefTarget) service;

        String moduleRelativeURL = GWT.getModuleBaseURL() + "gwtservice";

        endpoint.setServiceEntryPoint(moduleRelativeURL);

        return service;

    }

}

Step4:-Change the entry point of class MainEntryPoint.java.Modify the onModuleLoad() method of the class to the following :-


public void onModuleLoad() {



        RootPanel.get().add(new GWTServiceUsageExample());

    }

Step6:-In the Projects window, right-click the project node and choose Run.

Output of the program

Download source code