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 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

Interaction Levels Properties Bean Methods Event

Bean Framework Network Bean Container Bean

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

Introspection Introspector Methods Properties Events

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

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; } }

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 JavaBean API the same applies to retrieving the bean’s persistent values

Loading and Saving an Object

Saving an Object

Restoring an Object

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