JavaBeans Changes For J2SE 1.4

• JSR 57: Long Term Persistence for JavaBeans

• Beans Spec Amendment: Getting listeners

• Introspector changes

• Bean Builder Demo: Component Assembly

JSR 57: Long Term Persistence

• Included in J2SE 1.4 (Merlin) in the java.beans package

• New way of Serializing graphs of JavaBeans to an XML format

• Version resilience to changes in the VM

• Archives public state of the bean

• Tolerance to damaged archives.

Mechanics of Long Term Persistence

• XMLEncoder - Encodes an Object graph to XML

  • Takes an OutputStream as constructor argument
  • writeObject will encode the Object to the stream

• XMLDecoder - Decodes an Object graph from XML

  • Takes an InputStream as the construct argument
  • readObject will return the root of the Object graph

• Requires a nullary constructor and properties which conform to the JavaBeans Specification

• Use a subclass of PersistenceDelegate to encode JavaBeans which are not well formed.

Getting Listeners from JavaBeans

• EventSets are defined by the existence of the addFooListener(FooListener) and removeFooListener(FooListener) methods.

• There is no access to the JavaBeans listener lists.

• 1.3 introduced the method: Component.getListeners(Class)

• Beans Spec has been amended to support FooListeners[] getFooListeners()

New Design Patterns for Listeners

public void add<ListenerType>(<ListenerType l)

public void remove<ListenerType>(<ListenerType l)

public <ListenerType>[] get<ListenerType>s()

The existence of the the

ListenerType[] get<ListenerType>s()

method is completely optional

The Introspector will look for this method when EventSetDescriptors are created

Support for Named Properties

• For PropertyChangeListeners and VetoableChangeListeners

  void addPropertyChangeListener(String name, PropertyChangeListener l)

  void removePropertyChangeListener(String name, PropertyChangeListener l)

  PropertyChangeListener[] getPropertyChangeListeners(String name)

Affect of Named Properties on getPropertyChangeListeners()

• New class: PropertyChangeListenerProxy

• Returned listener array will contain a mix of PropertyChangeListeners and Proxies.

  

get<Foo>Listeners Conclusion

• All Swing and AWT classes have getFooListeners() methods added for 1.4

• The Introspector will use the getFooListeners() method if it exists to build the EventSets.

• EventSetDescriptor.getGetListenerMethod() will return the method to access the array of listeners or null if it doesn’t exist.

Changes to the Introspector

• Uses new 1.2 Collections classes

• Descriptors are sorted by the key FeatureDescriptor.getName(). However, this is not part of the Beans Spec.

• getBeanInfo() no longer returns a copy

Bean Builder Demo

• Showing how all the pieces fit together…

Conclusion

• Long term persistence is finally available!

• Add getFooListeners() methods to your Beans

• Introspector is faster and more deterministic.

• Watch the JavaBeans site for the Bean Builder and other emerging technologies

• http://java.sun.com/products/javabeans