GWT is a Java-based framework that allows developers to create complex JavaScript applications and deploy them as optimized JavaScript. It includes a widget library and allows communication with a server through simple RPC calls. GWT compiles Java code to optimized JavaScript that is minimized for efficient loading on browsers. It aims to ease the creation of both web pages and full web applications.

1. Intro
GWT
RPC
Demo
GWT
The Google Web Toolkit
Jeppe R. Thomsen
jenslyn@cs.aau.dk
Aalborg University
Department of Computer Science
October 6, 2009
Jeppe GWT - SW7 1/22

2. Intro GWT
GWT Motivation
RPC Application Areas
Demo Resources
The Presentation
Not the usual slide style
More text - less code
Interrupt if you are bored, and ask me something instead
E.g. ”You are boring, show me how to code X”
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3. Intro GWT
GWT Motivation
RPC Application Areas
Demo Resources
What is GWT - The Google Web Toolkit
It is among other things:
An AJAX framework
A Widget library
A Java-to-Javascript compiler
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4. Intro GWT
GWT Motivation
RPC Application Areas
Demo Resources
Motivation for using it
Communicate with your server through really simple RPC
Using e.g. JSON and XML
Optimize the JavaScript script downloads based on user
profile
Using Deferred binding
Reuse UI components across projects
Use other JavaScript libraries and native JavaScript code
Mix handwritten JavaScript in your Java code (JSNI)
Easily support the browser’s back button and history
adding state to the browser’s back button history
Localize applications efficiently
Test your code with JUnit
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5. Intro GWT
GWT Motivation
RPC Application Areas
Demo Resources
Application
GWT is, unlike many other AJAX frameworks, aimed at both
webpage- and webapplication- development.
The Javascript code is compiled to minimal size
The Javascript has any unreachable code purged at compile
time
Highly versatile and combinable UI widgets.
Java source language makes it realistic to do actual
application development in Javascript
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6. Intro GWT
GWT Motivation
RPC Application Areas
Demo Resources
Pros and Cons
Where to use it.
Webpages which needs to react to user actions immediately
Anywhere you would want some dynamic content on your
webpage
Where Not to use it.
Purely Static (informational) pages which does not change or
update often.
Anywhere it would be assumed users have disabled Javascript
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7. Intro GWT
GWT Motivation
RPC Application Areas
Demo Resources
GWT Resources
Download GWT
http://code.google.com/webtoolkit/
Widgets Demo
http://gwt.google.com/samples/KitchenSink/KitchenSink.html
Official Libraries
http://code.google.com/webtoolkit/googleapilibraries.html
Jeppe GWT - SW7 7/22

8. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Develop in Java
Use your favorite IDE
Eclipse 3.5
NetBeans 6.7
IDEA 8.1
IntelliJ 7+
Some standard libraries are emulated, others replaced by gwt
libraries
java.lang
java.lang.annotation
java.util
java.io
java.sql
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9. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Reference - libraries 1/3
com.google.gwt.i18n.client.DateTimeFormat
Replacement for the java.util.DateTime- Format class in
normal Java. This replacement only supports a subset of the
normal Java version.
com.google.gwt.i18n.client.NumberFormat
The same kind of replacement, but then for the
java.util.NumberFormat, again providing only a subset of its
features.
com.google.gwt.user.client.Timer
A simplified, browser-safe timer class that can be used to
mimic a threaded environment, and which allows you to
schedule tasks and actions. Its a simplified version of the
java.util.Timer class.
Jeppe GWT - SW7 9/22

10. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Reference - libraries 2/3
java.lang
ArithmeticException ArrayIndexOutOfBoundsException ArrayStoreException AssertionError
Boolean Byte CharSequence Character Class ClassCastException Cloneable Comparable
Deprecated Double Enum Error Exception Float IllegalArgumentException IllegalStateException
IndexOutOfBoundsException Integer Iterable Long Math NegativeArraySizeException
NullPointerException Number NumberFormatException Object Override Runnable
RuntimeException Short StackTraceElement String StringBuffer StringBuilder
StringIndexOutOfBoundsException SuppressWarnings System Throwable
UnsupportedOperationException Void
java.lang.annotation
Annotation AnnotationFormatError AnnotationTypeMismatchException Documented ElementType
IncompleteAnnotationException Inherited Retention RetentionPolicy Target
Jeppe GWT - SW7 10/22

11. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Reference - libraries 3/3
java.util
AbstractCollection AbstractList AbstractMap AbstractQueue AbstractSequentialList AbstractSet
ArrayList Arrays Collection Collections Comparator ConcurrentModificationException Date
EmptyStackException EnumMap EnumSet Enumeration EventListener EventObject HashMap
HashSet IdentityHashMap Iterator LinkedHashMap LinkedHashSet LinkedList List ListIterator Map
Map.Entry MissingResourceException NoSuchElementException PriorityQueue Queue
RandomAccess Set SortedMap SortedSet Stack TooManyListenersException TreeMap TreeSet
Vector
java.io
FilterOutputStream OutputStream PrintStream Serializable
java.sql
Date Time Timestamp
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12. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Coding
Modify the DOM
JSNI - The JavaScript Native Interface
public class JSNIExample {
static int myStaticField;
void instanceFoo(String s) { }
public native void bar(JSNIExample x, String s) /*-{
// Call instance method instanceFoo() on this
this.@com.google.gwt.examples.JSNIExample::instanceFoo(Ljava/lang/String;)(s);
// Call instance method instanceFoo() on x
x.@com.google.gwt.examples.JSNIExample::instanceFoo(Ljava/lang/String;)(s);
// Read static field (no qualifier)
@com.google.gwt.examples.JSNIExample::myStaticField = val + ” and stuff”;
}-*/;
}
Jeppe GWT - SW7 12/22

13. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Debug the Java code
Use hosted mode while developing. Only compile to JavaScript
when done.
Debug Java code as you normally would
Code runs as bytecode and served using an internal Jetty
instance
Most times changes are immediately visible by just refreshing
the integrated browser instead of relaunching hosted mode
Use GWT.log() to log user behavior and exceptions.
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14. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Run the Java code
Compile to JavaScript when done developing the application
Java code compiled to 6(7) permutations of JavaSript to
ensure optimal performance in most versions of major
browsers
IE
Firefox
Safari
Opera
Size of JavaScript code minimal.
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15. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Deploy the Javascript
Specify one or more <div> elements in a .html file
JavaScript will use them to hook bits of GWT functionality
into the existing page
Initial script will detect browser vendor and version
only download relevant permutation of JavaScript
public void onModuleLoad() {
final Button sendButton = new Button(”Send”);
final TextBox nameField = new TextBox();
nameField.setText(”GWT User”);
sendButton.addStyleName(”sendButton”);
RootPanel.get(”nameFieldContainer”).add(nameField);
RootPanel.get(”sendButtonContainer”).add(sendButton);
}
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16. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Demo
Ask if you want something
specific demonstrated.
Jeppe GWT - SW7 16/22

17. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Basic Widgets
http://code.google.com/webtoolkit/doc/1.6/RefWidgetGallery.html
http://gwt.google.com/samples/Showcase/Showcase.html
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18. Intro Code-, Debug-, Run Java
GWT Deploy Javascript
RPC Demo
Demo Widgets & Panels
Combining Widgets
All widgets can be combined and extended
support ease of use
allow reusing advanced and specialized widgets which still
compile to efficient JavaScript
Many advance widget libraries already exist (e.g. SmartGWT)
Jeppe GWT - SW7 18/22

19. Intro
Motivation
GWT
Plumbing
RPC
Server Communication
Demo
RPC
Allows a GWT client to make a call to server-side code
Super easy development. All the proxy classes that handle
RPC are generated automatically. All you need to do is define
your service’s interface and its server-side implementations.
GWT client serialization allows client JavaScript to interact
with Java classes on the server
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20. Intro
Motivation
GWT
Plumbing
RPC
Server Communication
Demo
Plumbing
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21. Intro
Motivation
GWT
Plumbing
RPC
Server Communication
Demo
Server Communication
Creating Services - Three steps
Define the service’s synchronous and asynchronous
interfaces
Implement the service
Call the service
Exception Handling
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22. Intro
GWT
RPC example
RPC
Demo
Demo
RPC Demonstration
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