Java Beans

Java Beans

Software Components

JavaBeans are classes that encapsulate many objects into a single object. They are serializable, have a zero-argument constructor, and allow access to properties using getter and setter methods.

A bean is a Java class with method names that follow the JavaBeans guidelines. A bean builder tool uses introspection to examine the bean class. Based on this inspection, the bean builder tool can figure out the bean’s properties, methods, and events.
Almost any code can be packaged as a bean.
The power of JavaBeans is that you can use software components without having to write them or understand their implementation.

Java Beans Example

import java.io.Serializable;

public class Car implements Serializable {
    //Private Properties
    private String color;
    private Boolean isCar;

    //Zero-argument Constructor
    public Car(){}

    //Getter and Setter
    public void setColor(String color) { this.color = color; }
    
    public String getColor() { return color; }
    
    public void setCar(Boolean car) { isCar = car; }

    //'is' for Boolean getter
    public Boolean isCar() { return isCar; }
}

Bean Properties

• Indexed Properties
  an array instead of a single value
• Bound Properties
  PropertyChangeListeners
• Constrained Properties
  VetoableChangeListeners

Bean Methods

Any public method that is not part of a property definition is a bean method.

Bean Events

• A bean class can fire off any type of event
• Method names with a specific pattern
• Can be used in wiring components together

BeanInfo

A BeanInfo is a class that changes how your bean appears in a builder tool.

Bean Persistence

Serialization

A bean has the property of persistence when its properties, fields, and state information are saved to and retrieved from storage.
All beans must persist. To persist, must implement either of below:

• java.io.Serializable
• java.io.Externalizable

Any class is serializable as long as that class or a parent class implements the java.io.Serializable interface.
Examples:

• Component
• String
• Date
• Vector
• Hashtable

Not serializable:

• Image
• Thread
• Socket
• InputStream

Controlling Serialization:

• Automatic serialization
• Customized serialization
• Customized file format

Long Term Persistence

Long-term persistence is a model that enables beans to be saved in XML format.

Links

JavaBeans
Oracle’s JavaBeans tutorials
JavaBeans specification
初识Spring —— Bean的装配（一）

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