An Overview of the Google Web Toolkit GWT

An Overview of the Google Web Toolkit (GWT) November 15, 2006 1

Introduction • Who am I? • My development experience: C++, Java, . NET • Why GWT? 2

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) 3

What is AJAX? • Asyncrhonous Xml And Javascript • Centered around the XMLHttp. Request object • AJAX request types: • Fire and forget (do. Post in Servlet parlance) • Asynchronous (request/callback) • Enables Event Handling paradigm/semantics • Implemented using Javascript 4

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? js. Unit 5

AJAX Advantages • Sexy • Looks great on a resume! • Lends itself to great pick up lines 6

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 7

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) 8

So what can we use to address these disadvantages? 9

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 10

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? 11

In Java! 12

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 13

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? ) 14

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 15

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 16

Archive Contents • Command-line utilities: project. Creator, application. Creator, i 18 n. Creator, junit. Creator • Platform Development Jar: gwt-dev-xxx. jar – where xxx is win 32, linux, mac • Deployment Jar: gwt-user. jar • Sample Applications • API Documentation 17

Layout of Significant Packages • core. client: • GWT (uncaught exception handler) • Javascript. Exception • Entry. Point Interface • user. client – Browser history, DOM manipulation, event handling etc • user. client. rpc – Client side implementation classes of RPC (Is. Serializable, Async. Callback) • user. client. ui – UI Widgets, Panels and other classes to support GUI 18

Getting Started Developing with GWT • First things first, we need an Eclipse project: 1. 2. 3. 4. 5. Manually create a directory in your workspace Create project files with project. Creator Create application with application. Creator Import project into Workspace Grip it and rip it! …err, run the app 19

Project Creator • project. Creator, creates specific project artifacts • Src/bin directories • . project file • . classpath file • In the case of Eclipse, workspace folder must exist already: project. Creator -ant Foo -eclipse Foo • Ant build file creates targets for compile, package and clean. 20

Application 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) application. Creator –eclipse Foo com. daugherty. gwtdemo. client. Application 21

Project 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. ) 22

Modes 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 23

The Application • Synonymous with C/C++, Java and C# main methods • Implementation of the Module entry point public interface Entry. Point { public abstract void on. Module. Load(); } 24

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 25

Application Example public class Application implements Entry. Point { public void on. Module. Load() { final Button button = new Button("Click me"); final Label label = new Label(); button. add. Click. Listener(new Click. Listener() { public void on. Click(Widget sender) { if (label. get. Text(). equals("")) label. set. Text("Hello World!"); else label. set. Text(""); } }); Root. Panel. get("slot 1"). add(button); Root. Panel. get("slot 2"). add(label); } } 26

user. client. ui Package • Contains basic UI abstractions: Text. Box, Password. Text. Box, Grid, Label, Listbox, Menu. Bar, Menu. Item, Tree, HTMLTable • All UI elements descend from Widget • Panel abstractions include: Panel, Vertical. Panel, Horizontal. Panel, Deck. Panel, Dock. Panel, Root. Panel • Panels are composites, support whole/part hierarchies 27

More Detailed Sample Vertical. Panel display = new Vertical. Panel(); Horizontal. Panel panel = new Horizontal. Panel(); panel. set. Spacing(2); // Add a label panel. add(new Label("Time: ")); // Create a text box textbox = new Text. Box(); textbox. set. Size("75 px", "25 px"); textbox. add. Focus. Listener(create. Focus. Listener()); textbox. set. Focus(true); panel. add(textbox); display. add(panel); display. add(create. Button. Panel()); Root. Panel. get(). add(display); 28

Event Handling • GWT supports a wide selection of event handling interfaces and semantics, samples include: • • • Keyboard. Listener Mouse. Listener Click. Listener Source. Click. Listeners And many more - seriously, tons more. • UI elements have methods for adding and removing the event handlers 29

Click. Listener Sample • An interface used for click events. • Buttons etc. Click. Listener listener = new Click. Listener() { public void on. Click(Widget sender) { String value = textbox. get. Text(); if (value != null && !"". equals(value)) { // do something with value… } } }; my. Button. add. Click. Listener(listener); 30

Service 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 31

Service “Plumbing” Diagram 32

So how do we do this? • Create a client-side interface to represent the service • Server-side abstraction is a Servlet - extends GWT’s Remote. Service. Servlet • Create an asynchronous interface – GWT uses this to generate the proxy • Make the call 33

Sample User Story: • User enters time which is validated and formatted (data entry validation) 34

Create Client-side Interface • Extends GWT Remote. Service • Regular Java interface - nothing special public interface Time. Format. Service extends Remote. Service { public abstract String format. Time(String unformatted); } 35

Server-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 Remote. Service. Servlet (GWT base class for remote services) • Implements client-side interface • Hosted mode testing by mapping in Module XML 36

Servlet Code public class Time. Format. Service. Impl extends Remote. Service. Servlet implements Time. Format. Service { public String format. Time(String unformatted) { String result = ""; if (unformatted != null) { Time time = Time. Factory. create. Time(unformatted); result = time. to. String(); } return result; } } 37

Aysnchronous 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 Time. Format. Service. Async { public abstract void format. Time(String unformatted, Async. Callback callback); } 38

Making the Call • Create an instance of the Service Proxy GWT. create() • This is the weird part: Cast the client interface to a Service. Def. Target • Set the Module Entry point on the above target (URL) • Create Asynchronous callback - handles on. Success and on. Failure • Call client-side remote proxy passing the arguments and the callback 39

What this looks like Time. Format. Service. Async time. Service = (Time. Format. Service. Async) GWT. create(Time. Format. Service. class); Service. Def. Target endpoint = (Service. Def. Target) time. Service; String module. Relative. URL = GWT. get. Module. Base. URL() + "time"; endpoint. set. Service. Entry. Point(module. Relative. URL); Async. Callback callback = new Async. Callback() { public void on. Failure(Throwable object) { // Failure path } public void on. Success(Object object) { // Success path } }; time. Service. format. Time(value, callback); 40

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 41

Debugging Sample With IDE 42

Wrapping Up • Full UI abstractions for Web applications • Allows for remoting of Objects that implement Is. Serializable • Surprisingly mature API • Well supported • Finally! Java code that generates to a Web GUI • Much more than has been shown here 43

Questions, Comments, Suggestions? 44

Beer? ? ? 45

Thank You!!! 46