GWT Training - Session 3/3

GWT Training – Session III Communicating with the Server

Contents

Asynchronous HTTP Request

Submitting Data using HTML Form

Traditional

GWT

GWT RPC

Asynchronous HTTP Requests

/ /create a new GET request

RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, "/info.php”);

try{

//send the request

builder.sendRequest( null, new RequestCallback() {

public void onError(Request request, Throwable exception){

//log the error

}

public void onResponseReceived(Request request, Response response){

//process response

}

});

}

catch (RequestException e){

//handle request exception

}

Asynchronous HTTP Requests – cont'd

builder.sendRequest() method receives a string data to be sent with the request and RequestCallback object that handles the response from the server

null is passed if there is no data to be sent to the data

Submitting Data to Server Using HTML Form

<form name="input" action="register.php" method="post">

Username: <input type="text" name="user"><br/>

Email: <input type="text" name="email"><br/>

Password: <input type="password" name="password"><br/>

<input type="submit" value="Submit">

</form>

Data Submitted

POST /register.php HTTP/1.1

Content-Type: application/x-www-form-urlencoded

username=Faiz&email=faizbash%40gmail.com&password=secret

GWT Equivalent for Form Data Submission - Constructing HTTP Request Manually

//build the data to post

StringBuffer postBuilder = new StringBuffer();

postBuilder.append("username=" );

postBuilder.append( URL.encodeComponent( username ) );

postBuilder.append("&email=" );

postBuilder.append( URL.encodeComponent( email ) );

postBuilder.append("&password=" );

postBuilder.append( URL.encodeComponent( password ) );

try{

//create and submit the request

RequestBuilder requestBuilder = new RequestBuilder( RequestBuilder.POST,

GWT.getModuleBaseURL()+"/register.php" );

requestBuilder.sendRequest( postBuilder.toString(), new RequestCallback(){

public void onError(Request request, Throwable exception){

// handle error

}

public void onResponseReceived(Request request, Response response){

// handle response

}

});

}catch( Exception e){ // handle exception }

GWT Equivalent for Form Data Submission – Using FormPanel

//create the form panel, set its action and method

final FormPanel form = new FormPanel();

form.setAction("/register.php");

form.setMethod(FormPanel.METHOD_POST);

//set the main widget for the panel to a vertical panel

VerticalPanel panel = new VerticalPanel();

form.setWidget(panel);

//create the username field

TextBox tb = new TextBox();

tb.setName("username");

panel.add(tb);

//create the e-mail field

TextBox tb = new TextBox();

tb.setName("email ");

panel.add(tb);

GWT Equivalent for Form Data Submission – Using FormPanel (cont'd)‏

//create the password field

PasswordTextBox ptb = new PasswordTextBox();

ptb.setName("password");

panel.add(ptb);

//create the Submit button

Button submit = new Button(“Submit”);

submit.addClickHandler( new ClickHandler() {

public void onClick(Widget sender) {

form.submit();

}

});

//add submit button to panel

panel.add(submit);

GWT RPC

GWT extends a browser’s capability to asynchronously communicate with the server by providing a remote procedure call (RPC) library.

Calls to the server are simplified by providing you with an interface of methods that can be called similarly to regular method calls.

GWT marshal the calls (convert to a stream of data) and send to the remote server.

At the server side, the data, is un-marshalled the method on the server is invoked

GWT RPC – cont'd

In GWT, the RPC library is divided into two packages:

com.google.gwt.user.client.rpc package used for client-side RPC support

com.google.gwt.user.server.rpc package used for server-side RPC support The client side provides interfaces that you can use to tag

When the client code is compiled to Javascript using the GWT compiler, the code required to do the RPC marshaling will be generated

GWT RPC Implementation

To understand how GWT RPC works, we would implement the data form submission using it

GWT RPC Implementation – Step 1

Create the RPC interface (stub) on the client side

Create a new interface named LoginService under the my.utm.kase.gwttraining.client package

Edit the code to look like the one below:

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

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

@RemoteServiceRelativePath("login")‏

public interface LoginService extends RemoteService {

boolean login(String username, String email, String password);

}

Add the following in /war/WEB-INF/web.xml

Configure the servlet

Add the following in /war/WEB-INF/web.xml <servlet>

<servlet-name>loginServlet</servlet-name>

<servlet-class>

my.utm.kase.gettraining.server.LoginServiceImpl

</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>loginServlet</servlet-name>

<url-pattern>/gwttraining/login</url-pattern>

</servlet-mapping>

Create an async counterpart interface of the LoginService. This interface defines the callback method that will be called when the server generates a response

Create another interface, LoginServiceAsync under my.utm.kase.gwttraining.client package

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

public interface LoginServiceAsync {

boolean login(String username, String email,

String password, AsyncCallback<Boolean> callback);

}

The async method always returns void and takes parameters similar to its stub counterpart plus an AsyncCallback parameter which specifies the return value of the stub method which is Void in this case

Implement the remote method on the server side

Create a class, LoginServiceImpl under my.utm.kase.gwttraining.server package

import my.utm.kase.gwttraining.client.LoginService;

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

public class LoginServiceImpl extends RemoteServiceServlet implements LoginService {

public boolean login(String username, String email, String password)‏

{

if( username.equals("faizbash") && password.equals("secret") )

{

return true;

}

else return false;

}

}

Call the remote method

Create a login widget in my.utm.kase.gwttraining.client package to get username, email and password from user. It also captures login event and makes a RPC to loign user.

public class LoginWidget extends Composite {

public LoginWidget() {

//login panel

FlexTable loginTable = new FlexTable();

final TextBox usernameBox = new TextBox();

final TextBox emailBox = new TextBox();

final PasswordTextBox passwordBox = new PasswordTextBox();

Button loginButton = new Button("Login");

loginButton.addClickHandler( new ClickHandler() {

public void onClick(ClickEvent event) {

login(usernameBox.getText(), emailBox.getText(), passwordBox.getText();

}

});

//username widget

loginTable.setWidget(0, 0, new Label("Username"));

loginTable.setWidget(0, 1, usernameBox);

//email widget

loginTable.setWidget(1, 0, new Label("Email"));

loginTable.setWidget(1, 1, emailBox);

GWT RPC Implementation – Step 5 (cont'd)‏

//password widget

loginTable.setWidget(2, 0, new Label("Password"));

loginTable.setWidget(2, 1, passwordBox);

//login button widget

loginTable.setWidget(3, 0, loginButton);

loginTable.getFlexCellFormatter().setColSpan(3, 0, 2);

//init loginTable

initWidget(loginTable);

}

public void login(String username, String email, String password) {

//create a callback method

AsyncCallback<Boolean> callback = new AsyncCallback<Boolean>() {

public void onFailure(Throwable caught) {

//handle failure

Window.alert("Failed to login");

}

public void onSuccess(Boolean status) {

if( status )‏

Window.alert("Login successful");

else

Window.alert("Invalid username or passord");

}

};

GWT RPC Implementation – Step 5 (cont'd)‏

//Create a remote service proxy to talk to the server-side Greeting service.

final LoginServiceAsync loginService = GWT.create(LoginService.class);

//invoke the remote method

loginService.login(username, email, password, callback);

}

}

Instantiate the widget in the GWTTrainingWidgets entry point class:

//login widget

LoginWidget loginWidget = new LoginWidget();

tabPanel.add(loginWidget, "Login");

Run or refresh to test

Thank you

GWT Training - Session 3/3

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