CS696: Doc 3, Remote AWT

	CS 696 Emerging Technologies: Java Distributed Computing Spring Semester, 1999 Remote AWT
	Previous Lecture Notes Index Next © 1999, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 01-Feb-99

Contents of Doc 3, Remote AWT

How does RAWT work

Background

RAWT Components

References
Remote AWT (RAWT) for Java documentation

You can learn more about RAWT and download it at:
http://www.alphaWorks.ibm.com/formula.nsf/system/technologies/51A3BC3A88D2B00A882565CE007F61F5?OpenDocument

Design Patterns: Elements of Reusable Object-Oriented Software , Gamma, Helm, Johnson, Vlissides, 1995, Abstract Factory pp. 87-96, Singleton pp. 127-134, Bridge pp.151-162.


Doc 3, Remote AWT Slide # 2

Remote AWT (RAWT)
RAWT

Runs Java AWT programs across any TCP/IP network
Does not use X windows
AWT programs run remotely without any modification
Does support Swing, but is not optimized for Swing
Uses JDK 1.1.6 or JDK 1.1.7
Will be converted to JDK 1.2 & optimized for Swing
Developed at IBM, available from alphaworks ( http://www.alphaWorks.ibm.com )


Doc 3, Remote AWT Slide # 3

How does RAWT work

Background

Peers
All AWT components use peers

The peer does the platform specific operations for the component, including drawing on the screen

Each component has its own type of peer

The java.awt.peer package (JDK1.2)contains the following peer interfaces:

ButtonPeer.java
CanvasPeer.java
CheckboxMenuItemPeer.java
CheckboxPeer.java
ChoicePeer.java
ComponentPeer.java
ContainerPeer.java
DialogPeer.java
FileDialogPeer.java
FontPeer.java
FramePeer.java
LabelPeer.java
LightweightPeer.java

ListPeer.java
MenuBarPeer.java
MenuComponentPeer.java
MenuItemPeer.java
MenuPeer.java
PanelPeer.java
PopupMenuPeer.java
ScrollbarPeer.java
ScrollPanePeer.java
TextAreaPeer.java
TextComponentPeer.java
TextFieldPeer.java
WindowPeer.java

(Note: the java.awt.peer package does not appear in the standard on-line Java API documentation)

Swing components also use “basic” peers to perform low-level operations


Doc 3, Remote AWT Slide # 4

ToolKit
Each platform contains classes that implement each of the peer interfaces in the java.awt.peer package

These peer implementations do use native code

java.awt.ToolKit

Is an abstract class
Defines methods to create any peer
Each JVM uses a concrete subclass of ToolKit to create peers

All AWT/Swing components create peers using the Toolkit

The code used by the Button class to get its peer reduces to:

   ToolKit myToolKit = Toolkit.getDefaultToolkit();
   peer = myToolKit.createButton(this);

(Note: this code is a simplified version of what actually happens)


Doc 3, Remote AWT Slide # 5

Changing the Default ToolKit
The name of the class used for the ToolKit implementation is a system property.

The following code will print out the name of the class being used as the ToolKit implementation:

   System.out.println( System.getProperty( "awt.toolkit" ));

The following code will print out all current system property keys:

Enumeration systemPropertyKeys = System.getProperties().propertyNames();

while ( systemPropertyKeys.hasMoreElements() )
System.out.println( systemPropertyKeys.nextElement() );

The –D flag of the command java sets system properties

The following code will set system property “awt.toolkit” to edu.sdsu.whitney.SimpleToolKit when running the program foo

java -Dawt.toolkit=edu.sdsu.whitney.SimpleToolKit  foo
Doc 3, Remote AWT Slide # 6

AWT and Design Patterns
For those that know about design patterns

AWT Peers are an example of the use of the Bridge pattern

The Singleton pattern is used to insure there is only one default ToolKit. Toolkit.getDefaultToolkit() returns the singleton

The ToolKit class is an example of the Abstract Factory pattern, which is sometimes called a Kit


Doc 3, Remote AWT Slide # 7

RAWT Components

Server

Server code
Component Classes which send responses back to client

Client

Peer implementations
Code to talk to server

Protocol

Client & Server need to agree on how to create AWT components and send AWT events to each other

Start server on machine to display application GUI

   java com.ibm.rawt.server.RAWTPCServer

Start application on client machine using:

   java -Dawt.toolkit=com.ibm.rawt.client.CToolkit -DRmtAwtServer=ServerIP ApplicationMainClass

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