Javaone2008 Bof 5102 Groovybuilders

Cooking your own Groovy Builder: A step forward into Domain-Specific Languages Ixchel Ruiz, PSE CCA Andres Almiray, PSE Oracle BOF-5102

Learn to empower your code with the expressiveness of Groovy’s Builders

Agenda
Builders and Groovy
Life without builders
Swing demo
Java2D demo
FactoryBuilderSupport
Resources

Why Groovy?
It is so Cool !
No impedance mismatch with Java
Groovy is Java
Flat learning curve
If you are a Java programmer, congratulations! you are also a Groovy programmer

Builders
Provide an abstraction layer
Increase Expressiveness
Better suited to express hierarchical data
Simplify Development

Why builders for DSLs?
Domain-Specific Languages can be written with Groovy in many ways.
Metaprogramming
Fluent Interface, static imports, closures
Builders

Builders for DSLs
Builders are a great choice to begin with
Pretty straight forward structure
No heavy metaprogramming required
Groovy provides 2 base classes to get you started
BuilderSupport
FactoryBuilderSupport

The Dark Side
Life without builders

Swing
How many lines of code may this little program require in plain Java?

Groovy’s answer
import groovy.swing.SwingBuilder
import java.awt.BorderLayout as BL
import javax.swing.JOptionPane
SwingBuilder.build {
frame( id: 'frame', title: 'Hello World', show: true, pack: true ){
borderLayout()
label( 'Enter a message:', constraints: BL.WEST )
textField( id: 'name', columns: 20, constraints: BL.CENTER )
button( 'Click', constraints: BL.EAST, actionPerformed: { e ->
if( !name.text ) return
JOptionPane.showMessageDialog( frame, name.text )
})
}
}

Java2D This is a Java2D drawing that started as a rounded rectangle

How many lines of code would it take in plain Java?
Short answer: didn’t even bother to measure them
The complete example has a little animation, applying each filter at a time, wonder how much code would be needed

Groovy’s answer
antialias on
rect( x: 20, y: 20, width: 180, height: 160,
arcWidth: 50, arcHeight: 50, borderColor: no, id: 'base' ){
linearGradient {
stop( offset: 0.5, color: 'white' )
stop( offset: 1, color: 'blue' )
}
filters( offset: 50 ){
weave()
kaleidoscope( sides: 4 )
shapeBurst( merge: true, type: 'circle up' )
lights(){
ambientLight( color: color('lime').rgb(),
centreX: 0, centreY: 0 )
}
dropShadow()
}
}

What is going on?
As with other builders, each node is actually a “pretended” method
Pretended methods are routed through the build cycle, any other methods are handled as usual
SwingBuilder node names are easy to remember, most of the time just remove the leading ‘J’ from a Swing class and that’s it
Both SwingBuilder and GraphicsBuilder extend from FactoryBuilderSupport

FactoryBuilderSupport at a glance
Factories have the responsibility to handle pretended methods
Each factory hooks into the build cycle
The builder will notify the current building factory whenever an action on the node should be taken
Each factory has it own context for storing useful information while building nodes

What factories may control
Node creation
Setting attributes on the node
If the node accepts children
Adding the node to its parent node
Processing the closure by themselves or let the builder handle it
Node completion

Available context properties (1)
context : retrieves the current context
current : reference to the current node
currentName : the “pretended” method name
currentFactory : reference to the factory that built the current node

Available context properties (2)
Similar properties if a parent node is available
parentContext : retrieves the parent’s context
parentNode : reference to the parent node
parentName : the parent’s node name
parentFactory : reference to the parent’s factory

Extension Points
FactoryBuilderSupport exposes the following extension points via closure delegates
Pre node creation
Post node creation
Attribute handling
Node completion
End of build cycle

Adding css to Swing, how?
We can’t extend every swing component available, that’s overkill
We can’t also extend every factory for the same reason
But we can use an attribute delegate that handles css attributes

This is one way to do it
import groovy.swing.*
import com.u2d.css4swing.CSSEngine
import com.u2d.css4swing.style.ComponentStyle
CSSEngine.initialize()
SwingBuilder.build {
addAttributeDelegate { builder, node, attributes ->
def cssClass = attributes.remove("cssClass")
if( cssClass ) ComponentStyle.addClass( node, cssClass )
}
frame( id: 'fame', size: [300,100], locationRelativeTo: null,
title: 'CSS+ Swing + Groovy', show: true ){
gridLayout( cols: 1, rows: 2 )
label( 'This is not important' )
label( 'This is really important', cssClass: 'important' )
}
}

Live code session

For More Information
http:// groovy.codehaus.org
The builders
http:// groovy.codehaus.org/FactoryBuilderSupport
http:// groovy.codehaus.org/ObjectGraphBuilder
http:// groovy.codehaus.org/Swing+Builder
http:// groovy.codehaus.org/SwingXBuilder
http:// groovy.codehaus.org/JideBuilder
http://groovy.codehaus.org/GraphicsBuilder
http://groovy.codehaus.org/Using+Ant+from+Groovy
http://groovy.codehaus.org/Creating+XML+using+Groovy's+MarkupBuilder
http:// jroller.com/aalmiray

Andres Almiray, PSE Oracle Ixchel Ruiz, PSE CCA BOF-5102

Javaone2008 Bof 5102 Groovybuilders

by Andres Almiray

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