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In computing based on theJava Platform,JavaBeans is a technology developed bySun Microsystems and released in 1996, as part ofJDK 1.1.

The 'beans' of JavaBeans are classes that encapsulate one or moreobjects into a single standardized object (the bean). This standardization allows the beans to be handled in a more generic fashion, allowing easiercode reuse andintrospection. This in turn allows the beans to be treated assoftware components, and to be manipulated visually byeditors and IDEs without needing any initial configuration, or to know any internal implementation details.

As part of the standardization, all beans must beserializable, have azero-argument constructor, and allow access to properties usinggetter and setter methods.

Introspection

Introspection is a process of analyzing a Bean to determine its capabilities. This is an essential feature of the Java Beans specification because it allows another application, such as a design tool, to obtain information about a component.

Properties

A property is a subset of a Bean's state. The values assigned to the properties determine the behaviour and appearance of that component. They are set through a setter method and can be obtained by a getter method.

Customization

A customizer can provide a step-by-step guide that the process must follow to use the component in a specific context.

Events

Beans may interact with the EventObject EventListener model.^{[clarification needed]}

Persistence

Persistence is the ability to save the current state of a Bean, including the values of a Bean's properties and instance variables, to nonvolatile storage and to retrieve them at a later time.

Methods

A Bean should useaccessor methods toencapsulate the properties. A Bean can provide other methods for business logic not related to the access to the properties.

• The properties, events, and methods of a bean can be exposed to another application.
• A bean may register to receive events from other objects and can generate events that are sent to those other objects.^{[citation needed]}
• Auxiliary software can be provided to help configure a bean.^{[citation needed]}
• The configuration settings of a bean can be saved to persistent storage and restored.^{[citation needed]}

• A class with azero-argument constructor is subject to being instantiated in an invalid state.^[1] If such a class is instantiated manually by a developer (rather than automatically by some kind of framework), the developer might not realize that the class has been improperly instantiated. The compiler cannot detect such a problem, and even if it is documented, there is no guarantee that the developer will see the documentation.
• JavaBeans are inherently mutable and so lack the advantages offered byimmutable objects.^[1]
• Having to create getters for every property and setters for many, most, or all of them can lead to an immense quantity ofboilerplate code.

The JavaBeans functionality is provided by a set of classes and interfaces in thejava.beans package.

In order to function as a JavaBeanclass, an object class must obey certain conventions about method naming, construction, and behaviour. These conventions make it possible to have tools that can use, reuse, replace, and connect Java Beans.

The required conventions are as follows:

• The class must have a publicdefault constructor (with no arguments). This allows easy instantiation within editing and activation frameworks.
• The classproperties must be accessible usingget,set,is (can be used for Boolean properties instead of get),to and other methods (so-calledaccessor methods andmutator methods) according to a standardnaming convention. This allows easy automated inspection and updating of bean state within frameworks, many of which include custom editors for various types of properties. Setters can have one or more arguments.
• The class should beserializable. (This allows applications and frameworks to reliably save, store, and restore the bean's state in a manner independent of theVM and of the platform.)

packageorg.wikipedia.players;importjava.io.Serializable;importjava.util.List;publicclassPersonBeanimplementsSerializable{/** Properties **/privatebooleandeceased=false;privateList<String>list;/** Property "name", readable/writable. */privateStringname=null;/** No-arg constructor (takes no arguments). */publicPersonBean(){}publicList<String>getList(){returnlist;}publicvoidsetList(finalList<String>list){this.list=list;}/**     * Getter for property "name".     */publicStringgetName(){returnname;}/**     * Setter for property "name".     *     * @param value     */publicvoidsetName(finalStringvalue){this.name=value;}/**     * Getter for property "deceased"     * Different syntax for a boolean field (is vs get)     */publicbooleanisDeceased(){returndeceased;}/**     * Setter for property "deceased".     * @param value     */publicvoidsetDeceased(booleanvalue){deceased=value;}}

TestPersonBean.java:

packageorg.wikipedia.players;importjava.util.ArrayList;importorg.wikipedia.players.PersonBean;/** * Class "TestPersonBean". */publicclassTestPersonBean{/**     * Tester method "main" for class "PersonBean".     *     * @param arguments     */publicstaticvoidmain(String[]args){finalPersonBeanperson=newPersonBean();person.setName("Bob");person.setDeceased(false);person.setList(newArrayList<String>());// Output: "Bob is [alive]"System.out.printf("%s is %s%n",person.getName(),person.isDeceased()?" [deceased]":" [alive]");}}

<jsp:useBeanid="person"class="org.wikipedia.players.PersonBean"scope="page"/><jsp:setPropertyname="person"property="*"/><html><body>Name:<jsp:getPropertyname="person"property="name"/><br/>Deceased?<jsp:getPropertyname="person"property="deceased"/><br/><br/><formname="beanTest"method="POST"action="testPersonBean.jsp">Enteraname:<inputtype="text"name="name"size="50"><br/>Chooseanoption:<selectname="deceased"><optionvalue="false">Alive</option><optionvalue="true">Dead</option></select><inputtype="submit"value="Test the Bean"></form></body></html>

• Software packaging

• Oracle's JavaBeans tutorials
• JavaBeans specification

• Java platform
• Architectural pattern (computer science)
• Software design patterns

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