Google Web Toolkit (GWT) by Sherif Elsbaey بمؤتمر مطورى جافا الاول بالمنصورة

1. Google Web Toolkit
(GWT)
by
Sherif Elsbaey

2. AGENDA
 Introducing GWT
 Discover the GWT's benefits, capabilities
and limitations
 Building User Interface
GWT Widgets
Event handling
Apply styles

3. AGENDA
 Client-Side RPC Architecture
GWT RPC
Serializable type
Handling Exception
 Create, develop, execute and deploy GWT
Applications
 History management
 Internationalization
 JUnit Testing
 Javascript Native Interface (JSNI)

4. AGENDA
 GWT Best Practices
Security Issues
Performance Concerns
The GWT Incremental-command class
Caching in GWT
GWT Design Considerations
GWT Pitfalls and Issues

5. Introducing GWT

6. WHAT IS GWT?
Java software development framework that makes
writing AJAX applications easy
Google announced GWT at the JavaOne 2006
Let you develop and debug AJAX applications in the
Java language using Java development tools
Eclipse, Netbeans, IntelliJ, …
Provides Java-to-Javascript compiler and
development mode that helps you debug your GWT
applications

7. GWT SDK & TOOLS
GWT SDK: contains Java API
libraries, compiler, development server and tools
Plugin for Eclipse: provides IDE support for GWT
and App Engine web projects
Some other tools:
GWT Designer
Speed Tracer

8. TWO MODES OF RUNNING GWT APP
Development mode (hosted mode)
GWT application is run as Java bytecode within JVM
Take advantage of Java debugging
Production mode (web mode)
Your GWT application is run as pure Javascript and HTML
compiled from original Java source code
End user will only see the web mode version of your
application

11. Discover the GWT's
benefits, capabilities and
limitations

12. BENEFITS
 Develop Rich Web Apps, utilize client CPUs
 GWT is ultimate Ajax
 Take advantage from rich built-in Widgets
 Build new generation of distributed apps
 GWT transmits a tiny fraction of data compared to traditional
applications (should really be compared to real contenders – Java
Applets/Flex/Silverlight)
 Leverage various tools of Java programming for
writing, debugging, testing
Ex: Eclipse, IntelliJ, Netbeans, …
 No need to take care of browser incompatibilities and quirks
GWT compiler handles them
Support browser history, backward, forward

13. CAPABILITIES
 Java-based Object-Oriented designs are easier to communicate
and understand.
 Take advantage of Java refactoring, code completion, ...
 No need to write “excellent” Javascript code
Leverage your Java programming knowledge
 JUnit integration
 Internationalization
 DOM management

14. LIMITATIONS
 Not all of JDK supported (enough for large projects though)
 JSON is not as natural as in JS, parsing is clunky

15. GWT VS ?

16. GWT ARCHITECTURE OVERVIEW

17. Building User Interface

18. GWT USER INTERFACE
 GWT user interface classes are similar to those
in existing UI frameworks such as Swing and
SWT.
GWT widgets are rendered using dynamically-created HTML
rather than pixel-oriented graphics
 The Widget classes make it easier to
quickly build interfaces that will work
correctly on all browsers.

19. WIDGETS LIBRARY

20. WIDGETS LIBRARY

21. WIDGETS LIBRARY

22. WIDGETS LIBRARY

23. EVENT HANDLER
 Events in GWT use the handler model
similar to other user interface frameworks
A handler interface defines one or more methods that the
widget calls to announce an event
A class wishing to receive events of a particular type
implements the associated handler interface and then passes
a reference to itself to the widget to subscribe to a set of
events.

24. EVENT HANDLER
 Example
public void anonClickHandlerExample() {
Button b = new Button("Click Me");
b.addClickHandler(new ClickHandler() {
public void onClick(ClickEvent event) {
// handle the click event
}
});
}

25. APPLY STYLES
 GWT applications use CSS for visual
styling
 Update styles dynamically in Java code
 Associate style sheets with the project
Using a <link> tag in the host HTML page.
Using the <stylesheet> element in the module XML file

26. Client-Side RPC Architecture

27. GWT REMOTE PROCEDURE CALL
 Mechanism for interacting with server by invoking a
method
Ex: fetching data from server
 GWT RPC makes it easy for the client and server to
pass Java objects back and forth over HTTP
provides serialization mechanism to bridge between client and server
Any object that needs to send is a GWT Serialization type
 Proper use of GWT RPC can allow you to develop an
application where all the UI logic resides on the
client, leaving business logic on the server)
Resulting in an application with greatly improved performance, reduced
bandwidth, and reduced web server load

28. GWT-RPC DIAGRAM
• Calls greetingService.greetserver(“Ron”)
Browser • Client-side code serializes objects and generates
RPC request payload
• RPC Request is sent to the server
POST /sample HTTP/1.1
..snip..
5|0|6|http://gwtsite/sample/|29F
4EA1240F157649C12466F01
F46F60|com.test.client.Greetin
gService|greetServer|java.lang
.String|myInput|1|2|3|4|1|5|6|
GWT Service

29. GWT-RPC DIAGRAM
Browser
HTTP/1.1 200 OK
..snip..
//OK[1,["Hello, Ron!<br><br>I am
running jetty-6.1.x.<br><br>It
looks like you are using:<br>
Chrome/6.0.472.63"],0,5]
• Parses and deserializes the request payload
• Executes the greetingServer method
• Sends JSON serialized response to the client
GWT Service

30. GWT RPC PLUMBING ARCHITECTURE

31. IMPLEMENTING GWT RPC
 Define an interface for your service that extends
RemoteService and lists all RPC method
called “Synchronous Interface”
 Implement the service at server-side
This class extends RemoteServiceServlet and implement the created
interface
 Define an asynchronous interface to your service to be
called from the client-side code
Based on original service interface
Require caller to pass callback object that can be notified when async
call completes.

32. SERIALIZABLE TYPES
 GWT RPC method parameters and return types must be
serializable
These values will be transmitted across network between client and
server
 Java data types are already serializable
Primitive, such as char, byte, short, int, long, boolean, float, or double.
String, Date or primitive wrapper:
Character, Integer, Byte, Double, …
Array of serializable types
Serializable user-defined class

33. HANDLING EXCEPTION
 Making RPCs opens up the possibility of a variety
of errors
Networks fail, servers crash, and problems occur while
processing a server call
 GWT lets you handle these conditions in terms of Java
exceptions
 Caller should implement
AsyncCallBack.onFailure(Throwable) to handle exception

34. Create, develop, execute and
deploy GWT Applications

35. History management

36. GWT HISTORY MECHANISM
GWT applications use “history token” to help Ajax
developer activate browser history
The token will be saved in browser history as a URL fragment
Ex:
http://www.example.com/historyexample/HistoryExample.html#page
1
To enable history to your Ajax
Add a history token to the history stack when you want to enable
history event
Create an object that implements the ValueChangeHandler interface,
parses new token and changes the application state to match

37. Internationalization

38. INTERNATIONALIZATION
GWT offers multiple internationalization techniques
Static String Internationalization
Dynamic String Internationalization
Static String Internationalization
Extends Constants Interface
Extends Message Interface
Use properties files
Dynamic String Internationalization

39. JUnit Testing

40. JUNIT TESTING
GWT provides integration with the popular JUnit
unit testing framework
GWT allows JUnit test cases to run in either
development mode or production mode.

41. Javascript Native Interface (JSNI)

42. WHY JSNI?
Sometimes it's very useful to mix handwritten Javascript to Java
source code
Ex: access low-level browser functionality not exposed by the GWT API
You can use JSNI to:
Implement a Java method directly in JavaScript
Wrap type-safe Java method signatures around existing JavaScript
Call from JavaScript code into Java code and vice-versa
Throw exceptions across Java/JavaScript boundaries
Read and write Java fields from JavaScript
Use development mode to debug both Java source (with a Java debugger) and
JavaScript (with a script debugger)

43. RESOURCES
http://code.google.com/webtoolkit/
Main site for GWT
http://googlewebtoolkit.blogspot.com/
http://developerlife.com

44. Question & Answer