an overview of the google web toolkit (gwt)

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An Overview of the An Overview of the Google Web Toolkit (GWT)Google Web Toolkit (GWT)November 15, 2006

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IntroductionIntroduction

• Who am I?

• My development experience: C++, Java, .NET

• Why GWT?

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Why Google Webtoolkit?• Web-based application framework• AJAX enabled• Web 2.0• <insert yet another buzzword here>• Implement an HTML User Interface in Java• Compiles to:

• HTML and Javascript• AJAX-enables app using a binary remoting protocol

(proprietary Google technology)

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What is AJAX?

• Asyncrhonous Xml And Javascript• Centered around the XMLHttpRequest object

• AJAX request types: • Fire and forget (doPost in Servlet parlance)• Asynchronous (request/callback)

• Enables Event Handling paradigm/semantics• Implemented using Javascript

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Everybody loves Javascript - Just not me

• Originally created by Netscape • Now based on ECMA Spec• Not a strongly typed language• Not fully dynamically typed either (think Ruby)• Browser implementations are inconsistent• Fragile and difficult to debug (I write buggy code)• Unit testing Javascript? jsUnit

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AJAX Advantages• Sexy

• Looks great on a resume!

• Lends itself to great pick up lines

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Real AJAX Advantages• Finer grained requests/responses• Avoid full-page refreshes to update data• Just-in-time data retrieval• Reuse existing server-side logic/components

• Data validations in native language

• Richer UI functionality

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AJAX Disadvantages• Implemented differently by browser vendors• Javascript not an OO language• Inheritance, Polymorphism is possible, but

difficult• Encapsulation using Javascript objects works• Knowledge of DOM to manipulate elements

(really it’s a Javascript issue, not really AJAX)

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So what can we use to address these disadvantages?

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Frameworks, Frameworks, Frameworks

• Scriptaculous, DWR, home-grown in-house etc.• No clear leader, definitely no standard• Java developers are inherently averse to

Javascript – that’s the reality (or is it just me?)• Provide tested code and crosss-browser

support

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So what does Google do?So what does Google do?• Recognize these issues - they develop

webapps too!

• Ask the question:

• How should a Java developer develop sexy web-based AJAX-enabled applications?

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In Java!

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So what is Google Webtoolkit?

• A Rich Client Architecture for developing rich internet apps

• How Google describes it:“Google Web Toolkit (GWT) is a Java software development framework that

makes writing AJAX applications like Google Maps and Gmail easy for developers who don't speak browser quirks as a second language.”

http://code.google.com/webtoolkit

• Conceptually similar to Swing but HTML specific with web remoting capabilities

• Includes UI Widgets/Components, RPC mechanisms and native Javascript support

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Swing• UI’s based on Panels and Layout Managers• UI Widgets for trees, lists, text, labels etc.• Event Handling (Action Listeners, Keyboard

Handling, Mouse and Focus events)• Swing’s implementation of UI is based on UI

Delegate (pattern?)

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GWT

• Widgets include the usual suspects - text, passwords, tables and HTML abstractions

• Layouts based on Panels (vertical, horizontal, deck, dock, scroll, tab etc.)

• Event Handlers/Listeners (Change, Click, Focus, Keyboard, Mouse, Scroll, Tab)

• Also utilizes the UI Delegate pattern

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What? Where?• Can be downloaded from http://code.google

.com/webtoolkit• Supported platforms include: Windows, Linux

(GTK+) and Mac OSX • OSS-friendly license:

• UI Widgets: Apache 2.0• GWT Compiler: Proprietary non-distributable license

• Initial support for Eclipse

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Archive ContentsArchive Contents• Command-line utilities: projectCreator,

applicationCreator, i18nCreator, junitCreator• Platform Development Jar: gwt-dev-xxx.jar –

where xxx is win32, linux, mac• Deployment Jar: gwt-user.jar• Sample Applications• API Documentation

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Layout of Significant PackagesLayout of Significant Packages• core.client:

• GWT (uncaught exception handler)• JavascriptException• EntryPoint Interface

• user.client – Browser history, DOM manipulation, event handling etc

• user.client.rpc – Client side implementation classes of RPC (IsSerializable, AsyncCallback)

• user.client.ui – UI Widgets, Panels and other classes to support GUI

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Getting Started Developing with Getting Started Developing with GWTGWT

• First things first, we need an Eclipse project:

1. Manually create a directory in your workspace2. Create project files with projectCreator3. Create application with applicationCreator4. Import project into Workspace5. Grip it and rip it! …err, run the app

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Project CreatorProject Creator• projectCreator, creates specific project artifacts

• Src/bin directories• .project file• .classpath file

• In the case of Eclipse, workspace folder must exist already:

projectCreator -ant Foo -eclipse Foo

• Ant build file creates targets for compile, package and clean.

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Application CreatorApplication Creator• Command line utility to generate application

artifacts:• Default client packages• Main class, entry point implementation• Module XML file (more later)• .launch file for Hosted Mode (debug mode)

applicationCreator –eclipse Foocom.daugherty.gwtdemo.client.Application

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Project StructureProject Structure• com/example/cal - The project root package

contains module XML files• com/example/cal/client - Client-side source

files and subpackages• com/example/cal/server - Server-side code

and subpackages• com/example/cal/public - Static resources

that can be served publicly (think HTML, images etc.)

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Modes of OperandiModes of Operandi• GWT supports to modes:

• Hosted - uses a built-in Tomcat instance for run-time debug environment

• Web - compiled application deployed to a production (or non-production as the case may be) environment

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The Application• Synonymous with C/C++, Java and C# main

methods• Implementation of the Module entry point

public interface EntryPoint {public abstract void onModuleLoad();

}

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What is a Module?What is a Module?• An XML configuration• Specifies an entry point - an application class

that renders to HTML• Specifies servlet mapping for Hosted Mode• May inherit from other Modules

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Application ExampleApplication Examplepublic class Application implements EntryPoint {

public void onModuleLoad() { final Button button = new Button("Click me"); final Label label = new Label();

button.addClickListener(new ClickListener() { public void onClick(Widget sender) { if (label.getText().equals("")) label.setText("Hello World!"); else label.setText(""); } });

RootPanel.get("slot1").add(button); RootPanel.get("slot2").add(label); }}

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user.client.ui Packageuser.client.ui Package• Contains basic UI abstractions: TextBox,

PasswordTextBox, Grid, Label, Listbox, MenuBar, MenuItem, Tree, HTMLTable

• All UI elements descend from Widget• Panel abstractions include: Panel,

VerticalPanel, HorizontalPanel, DeckPanel, DockPanel, RootPanel

• Panels are composites, support whole/part hierarchies

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More Detailed SampleMore Detailed SampleVerticalPanel display = new VerticalPanel();

// Add a labelpanel.add(new Label("Time:"));

// Create a text boxtextbox = new TextBox();textbox.setSize("75px", "25px");

textbox.addFocusListener(createFocusListener());

panel.add(textbox);display.add(panel);display.add(createButtonPanel());RootPanel.get().add(display);

textbox.setFocus(true);

• HorizontalPanel panel = new HorizontalPanel();• panel.setSpacing(2);••

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Event HandlingEvent Handling• GWT supports a wide selection of event

handling interfaces and semantics, samples include:

• KeyboardListener• MouseListener• ClickListener• SourceClickListeners• And many many more - seriously, tons more.

• UI elements have methods for adding and removing the event handlers

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ClickListener SampleClickListener Sample• An interface used for click events.• Buttons etc.

ClickListener listener = new ClickListener() {public void onClick(Widget sender) {

String value = textbox.getText();if (value != null && !"".equals(value)){

// do something with value…}

}};

myButton.addClickListener(listener);

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Service RemotingService Remoting• Proprietary binary remoting protocol.• AJAX under the covers• Server-side service target is a Servlet• Hosted Mode deployed in Module XML• Repetitive steps to create a Service -

opportunity to refactor/abstract and write some “cool” OO code

• Steps are well defined

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Service “Plumbing” DiagramService “Plumbing” Diagram

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So how do we do this?So how do we do this?• Create a client-side interface to represent the

service• Server-side abstraction is a Servlet - extends

GWT’s RemoteServiceServlet• Create an asynchronous interface – GWT uses

this to generate the proxy• Make the call

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Sample User Story:

• User enters time which is validated and formatted (data entry validation)

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Create Client-side InterfaceCreate Client-side Interface• Extends GWT RemoteService• Regular Java interface - nothing special

public interface TimeFormatService extends RemoteService{

public abstract String formatTime(String unformatted);

}

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Server-side ServletServer-side Servlet• Lives in app.server package structure• This is different than the client package - “real”

Java code, does not get compiled by the GWT compiler

• Standard Servlet• Extends RemoteServiceServlet (GWT base

class for remote services)• Implements client-side interface• Hosted mode testing by mapping in Module

XML

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Servlet CodeServlet Codepublic class TimeFormatServiceImpl extends

RemoteServiceServlet implements TimeFormatService{

public String formatTime(String unformatted){

String result = "";if (unformatted != null){ Time time = TimeFactory.createTime(unformatted); result = time.toString();}

return result;}

}

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Aysnchronous InterfaceAysnchronous Interface• GWT generates remote proxy from this• Interface that mimics the client-side interface• Subtle differences• This is the actual wiring between client and

server - the underpinnings of GWT’s remoting

public interface TimeFormatServiceAsync{

public abstract void formatTime(String unformatted, AsyncCallback callback);

}

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Making the CallMaking the Call• Create an instance of the Service Proxy -

GWT.create()• This is the weird part: Cast the client interface

to a ServiceDefTarget• Set the Module Entry point on the above target

(URL)• Create Asynchronous callback - handles

onSuccess and onFailure• Call client-side remote proxy passing the

arguments and the callback

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What this looks likeWhat this looks likeTimeFormatServiceAsync timeService = (TimeFormatServiceAsync)

GWT.create(TimeFormatService.class);

ServiceDefTarget endpoint = (ServiceDefTarget) timeService;String moduleRelativeURL = GWT.getModuleBaseURL() + "time";endpoint.setServiceEntryPoint(moduleRelativeURL);

AsyncCallback callback = new AsyncCallback() { public void onFailure(Throwable object) { // Failure path }

public void onSuccess(Object object) { // Success path }};

timeService.formatTime(value, callback);

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Well? Did it work?Well? Did it work?• Hosted mode allows rapid development

feedback loop - with a caveat.• Supports Hosted Mode debugging through

Eclipse• Full debugging capabilities of the IDE

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Debugging Sample With IDE

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Wrapping UpWrapping Up• Full UI abstractions for Web applications• Allows for remoting of Objects that implement

IsSerializable• Surprisingly mature API• Well supported• Finally! Java code that generates to a Web

GUI• Much much more than has been shown here

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Questions, Comments, Suggestions?

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Beer???

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Thank You!!!