Java Beans & Serialization

1. Java Beans & Serialization CS-328 Dick Steflik

2. Java Beans • Java based component technology • originally developed to provide java with a component technology like vbx/ocx of VB • originally used for user interface widgets • currently used for server side componets • Requirements • Bean naming conventions • must be serializable, to support persistence

3. Bean Naming Conventions • “setters” • set or modify a bean property value • must start with “set” • “getters” • retrieve property values from a bean • must start with “get”

4. Bean Properties • Simple • represents a single property and can be defined with a pair of get/set methods • Indexed • represents an array of properties • Bound • a bound property notifies other objects when its value changes • generates a PropertyChange event with property name, old value and new value • Constrained • an object with constrained properties allows other objects to veto a constrained property value change • Constrained property listeners can veto a change by throwing a PropertyVetoException

5. Interaction Levels Methods Bean Properties Event

6. Bean Framework Bean Bean Bean Bean Network Bean Container Bean Network

7. Introspection • the processby which a builder tool finds out which properties, methods, and events a bean supports. • searching for classes and methods that follow certain naming conventions • by querying the BeanInfo of a class • BeanInfo is an interface whose methods allow the interrogation of a beans properties, methods and events

8. Introspection Methods Properties Events Introspector

9. Reflection • The core APIs used by the JavaBeans Introspector class • java.lang.reflect

10. a simple GasTank Bean Class Gastank implements Serializable{ private double capacity; private int percent_full; public void setCapacity(double pounds){ capacity = pounds; } public double getCapacity() { return Capacity; } public void setPercent_full( int p) { percent_full = p; } public int getPercent_full() { return percent_full; } }

11. Jarring the Bean • Beans are packaged in a java archive (jar) file • the jar utility comes with the JDK • the jar file must be explicitly in your class path • in JDK 1.2.x all AWT and Swing classes are beans

12. GUI Builders • Because of a bean’s naming convention the GUIs introspector can build a property sheet for each bean automatically • The GUI builder allows you to configure the bean as your app. Needs • Because the bean is serializable the configured properties can be saves by the GUI Builder

13. Beans Development Kit • Download the latest BDK from SUN • Comes with the Beanbox • allows building of bean applications • provides the jar utility • allows saving of configured beans

14. Persistance • for persistance a bean must implement the Serializable interface • java.io.Serializable • saving of the bean’s fields is automatic, you need do nothing, everything is done by the JavaBean API • the same applies to retrieving the bean’s persistent values

15. Loading and Saving an Object

16. Saving an Object

17. Restoring an Object

19. For more on JavaBeans • JavaBeans Home Page - http://java.sun.com/beans/