Java Beans Serialization CS328 Dick Steflik Java Beans

Java Beans & Serialization CS-328 Dick Steflik

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

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”

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 Property. Change 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 Property. Veto. Exception

Interaction Levels Methods Bean Properties Event

Bean Framework Bean Network Bean Container Bean Network

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 Bean. Info of a class • Bean. Info is an interface whose methods allow the interrogation of a beans properties, methods and events

Introspection Methods Properties Events Introspector

Reflection • The core APIs used by the Java. Beans Introspector class • java. lang. reflect

a simple Gas. Tank Bean Class Gastank implements Serializable{ private double capacity; private int percent_full; public void set. Capacity(double pounds){ capacity = pounds; } public double get. Capacity() { return Capacity; } public void set. Percent_full( int p) { percent_full = p; } public int get. Percent_full() { return percent_full; } }

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

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

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

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 Java. Bean API • the same applies to retrieving the bean’s persistent values

Loading and Saving an Object

Saving an Object

Restoring an Object

For more on Java. Beans • Java. Beans Home Page http: //java. sun. com/beans/