GWT Basics

GWT Basics

GWT Advantages

1. You're write client side code in Java instead of javascript.

- We can use the reliable, strongly-typed language for development

- Reuse your skills of Java, no need skills in javascript and CSS.

2. We can use complex Java on the client

- We can use java class such as String, array, Math class, ArrayList, HashMap, custom classes, etc.

3. We can send complex Java types to and from the server.

4. GWT provides a number of widget.

-- Such as DatePicker, Tree, SuggestBox, RichTextArea, Grid, TabBar and etc.

5. Full IDE-based Java support for development/debugging.

-- Client side is java code, so we can use all Java IDE development/debugging features, Google also provides GWT designer, we can drag and drop control and widget to desgin the web UI.

6. Debugging

- We can debug client side code just like any other Java application, using our IDE's debugger. This approach is much better than JavaScript debugger.

Testabilty

- We can use java to write code to test client side code just like other java code.

GWT Disadvantages


1. Big learning curve, especailly for non-java developer.

2. Cumbersome deployment.

-- We have to translate client java code to javascript, then deploy to server.

Unusual approach

-- Fundamentally different strategy than all other Ajax environments makes evaluation and management buyoff harder.

Approaches to Communicate with the server

Making Remote Procedure Calls (GWT RPC)

If serve side can be implemented using java, we can use GWT RPC. Using it we can pass Java objects to and from a server and transparently make calls to Java servlets and let GWT take care of low-level details like object serialization.

Retrieving JSON Data via HTTP

RequestBuilder builder = new RequestBuilder(RequestBuilder.GET, url);

try {

Request request = builder.sendRequest(null, new RequestCallback() {

public void onError(Request request, Throwable exception) {displayError("Couldn't retrieve JSON");}

public void onResponseReceived(Request request, Response response) {

if (200 == response.getStatusCode()) {

updateTable(asArrayOfStockData(response.getText()));

} else {

displayError("Couldn't retrieve JSON (" + response.getStatusText()

+ ")");

}

}

});

} catch (RequestException e) {displayError("Couldn't retrieve JSON");}

Making Cross-Site Requests for JSONP

Writing Asynchronous Callbacks

All the calls you make from the HTML page to the server are asychronous, in client side, we need to implemente a function that would be called when request succeeds or fails(Using AsyncCallback).

@RemoteServiceRelativePath("greet")

public interface GreetingService extends RemoteService {

String greetServer(String name) throws IllegalArgumentException;

}

public interface GreetingServiceAsync {

void greetServer(String input, AsyncCallback callback)

throws IllegalArgumentException;

}

private final GreetingServiceAsync greetingService = GWT.create(GreetingService.class);

greetingService.greetServer(textToServer, new AsyncCallback() {

public void onFailure(Throwable caught) {

// Show the RPC error message to the user

dialogBox.setText("Remote Procedure Call - Failure");

serverResponseLabel.addStyleName("serverResponseLabelError");

serverResponseLabel.setHTML(SERVER_ERROR);

dialogBox.center();

closeButton.setFocus(true);

}

public void onSuccess(String result) {

dialogBox.setText("Remote Procedure Call");

serverResponseLabel.removeStyleName("serverResponseLabelError");

serverResponseLabel.setHTML(result);

dialogBox.center();

closeButton.setFocus(true);

}

});

}

public class GreetingServiceImpl extends RemoteServiceServlet implements GreetingService {..} // at server side

Manage Events on the Client

GWT is event-based. Code executes in response to some event occurring.

This is just like Swing, we write handler to handle event.

HTML logout_link = new HTML("Sign Out");

logout_link.addClickListener(new ClickListener() {

public void onClick(Widget sender) {

if (Window.confirm("Do you really want to leave ?")) {

login_user = "";Window.Location.reload();

}

}

});

logout_link.addStyleName("hover-cursor");

Declarative Layout in XML with GWT UiBinder

API

GWT.log("")

Basic steps

Create application

webAppCreator -out MyWebApp -junit "C:\Documents and Settings\Administrator\.m2\repository\junit\junit\4.8.2\junit-4.8.2.jar" com.mycompany.mywebapp.MyWebApp

Run locally in development mode

ant devmode

Compile and run in production mode

ant build

ant war

Running unit tests

ant test.dev|test.prod|test

Code Example

Creating custom widgets

public class ImageButton extends Composite{

private HorizontalPanel hPanel;

private Image button_img;

private HTML button_text;

public ImageButton(String text, Image image) {

}

}

DateTimeSelection to set data and time.

Creating Composite

CreateAccount, ChangePasswd, Login

How to access image

public interface ImagePack extends ImageBundle, DisclosurePanelImages {

AbstractImagePrototype Logo();

AbstractImagePrototype delete();

}

public class ImageAccessor {

private static final ImagePack images = (ImagePack) GWT.create(ImagePack.class);

public static ImagePack getImages() {return images;}

}

titlePanel.add(ImageAccessor.getImages().Logo().createImage());

Resources:

http://code.google.com/webtoolkit

Google Web Toolkit: The new frontier of Rich Internet Applications

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