The document discusses Google Web Toolkit (GWT) Remote Procedure Calls (RPC) and how to implement RPC between a GWT client and server. It describes the key classes and interfaces used for RPC, how to define the service interface and implementation classes, deploying the service, and making an asynchronous call from the client to retrieve the response.

1. GWT - RPC

2. The Objects com.google.gwt.user.client.rpc.RemoteService com.google.gwt.user.client.rpc.AsyncCallback com.google.gwt.user.client.rpc.ServiceDefTarget com.google.gwt.user.server.rpc.RemoteServiceServlet

3. RPC plumbing diagram

4. RPC plumbing diagram package com.mycompany.client; import com.google.gwt.user.client.rpc.RemoteService; public interface MyAddService extends RemoteService { public int add(int a, int b); }

5. RPC plumbing diagram package com.mycompany.server; import com.google.gwt.user.server.rpc.RemoteServiceServlet; import com.mycompany.client.MyAddService; public class MyAddServiceImpl extends RemoteServiceServlet implements MyAddService{ public int add(int a, int b) { int z = a + b; return z; } }

6. RPC plumbing diagram package com.mycompany.client; import com.google.gwt.user.client.rpc.AsyncCallback; public interface MyAddServiceAsync { public void add(int a, int b, AsyncCallback callback); }

7. Deploy service Tomcat -> add Servlet Hosted mode -> modify module XML <module> <inherits name='com.google.gwt.user.User'/> <entry-point class='com.mycompany.client.MyApplication'/> <servlet path=&quot;/addService&quot; class=&quot;com.mycompany.server.MyAddServiceImpl“/> </module>

8. Actually making a call button.addClickListener( new ClickListener() { public void onClick(Widget sender) { AddServiceAsync addService = (AddServiceAsync) GWT.create(AddService.class); ServiceDefTarget endpoint = (ServiceDefTarget) addService; String moduleRelativeURL = GWT.getModuleBaseURL() + &quot;myAddService“; endpoint.setServiceEntryPoint(moduleRelativeURL); instantiate service interface set service implementation url

9. Actually making a call button.addClickListener( new ClickListener() { public void onClick(Widget sender) { AddServiceAsync addService = (AddServiceAsync) GWT.create(AddService.class); ServiceDefTarget endpoint = (ServiceDefTarget) addService; String moduleRelativeURL = GWT.getModuleBaseURL() + &quot;myAddService“; endpoint.setServiceEntryPoint(moduleRelativeURL); AsyncCallback callback = new AsyncCallback(){ public void onSuccess(Object result){ resultaatLabel.setText(result.toString()); } public void onFailure(Throwable caught) { resultaatLabel.setText(caught.getMessage()); } create an asynchronous callback to handle the result

10. Actually making a call button.addClickListener( new ClickListener() { public void onClick(Widget sender) { AddServiceAsync addService = (AddServiceAsync) GWT.create(AddService.class); ServiceDefTarget endpoint = (ServiceDefTarget) addService; String moduleRelativeURL = GWT.getModuleBaseURL() + &quot;myAddService“; endpoint.setServiceEntryPoint(moduleRelativeURL); AsyncCallback callback = new AsyncCallback(){ public void onSuccess(Object result){ resultaatLabel.setText(result.toString()); } public void onFailure(Throwable caught) { resultaatLabel.setText(caught.getMessage()); } }; addService.add(Integer.parseInt(aBox.getText()), Integer.parseInt(bBox.getText()), callback); } } ); actually make the call

11. Actually making a call button.addClickListener( new ClickListener() { public void onClick(Widget sender) { AddServiceAsync addService = (AddServiceAsync) GWT.create(AddService.class); ServiceDefTarget endpoint = (ServiceDefTarget) addService; String moduleRelativeURL = GWT.getModuleBaseURL() + &quot;myAddService“; endpoint.setServiceEntryPoint(moduleRelativeURL); AsyncCallback callback = new AsyncCallback(){ public void onSuccess(Object result){ resultaatLabel.setText(result.toString()); } public void onFailure(Throwable caught) { resultaatLabel.setText(caught.getMessage()); } }; addService.add(Integer.parseInt(aBox.getText()), Integer.parseInt(bBox.getText()), callback); } } );

12. code executed on client side code executed on server side

13. Service Implementation Path This can be done in two ways – 1. Using RemoteServiceRelativePath annotation @RemoteServiceRelativePath(&quot;greet&quot;) public interface GreetingService extends RemoteService { String greetServer(String name) throws IllegalArgumentException; } 2. Using ServiceDefTarget ServiceDefTarget endPoint = (ServiceDefTarget) greetingService; endPoint.setServiceEntryPoint(GWT.getModuleBaseURL() + “greet” ); Reference: Common Pitfalls section of h ttp://code.google.com/webtoolkit/doc/1.6/DevGuideServerCommunication.html

14. Servlet Mapping GWT modules may declare one or more <servlet> tags. These define Java Servlets that implement the server-side component of a GWT-enabled web application. Prior to GWT 1.6, these GWT module servlet tags controlled the set of servlets were actually instantiated during hosted mode. But as of GWT 1.6, this is no longer true. Instead, the web application's WEB-INF/web.xml configuration file controls what servlets are instantiated. A GWT module specifies only what servlets are expected . During hosted mode startup, the set of expected servlets (from GWT module <servlet> tags) is validated against the set of actual servlets (from the WEB-INF/web.xml) and a warning is issued for each expected servlet which does not match an actual servlet. Reference: gwt-2.0.3/doc/helpInfo/servletMappings.html

15. More info http://code.google.com/webtoolkit/doc/latest/DevGuideServerCommunication.html

16. … and explore more by practice Thanking You Mahesh Babu M