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 <title>EJB architecture</title>
 </head>
 <body id="cearch"><a name="cearch"><!-- --></a>

 <h1 class="topictitle1">EJB architecture</h1>
 <div><p>This topic provides a high-level overview of the distributed component
 architecture defined in the Sun Microsystems Enterprise JavaBeans™ (EJB)
 architecture specification.</p>
 <p>The complete Enterprise JavaBeans specifications and descriptions
 of the technology are available from the <a href="http://java.sun.com/products/ejb/docs.html#specs" target="_blank">java.sun.com</a> Web site.</p>
 <p>Enterprise beans provide several benefits for application developers: </p>
 <ul><li>They allow you to build distributed applications by combining components
 developed using tools from different vendors. </li>
 <li>They make it easy to write applications. You do not have to deal with
 low-level details of transaction and state management, multithreading, resource
 pooling, and other complex low-level APIs. However, if necessary, expert programmers
 can still gain direct access to the low-level APIs.</li>
 <li>They can be developed once and then deployed on multiple platforms without
 recompilation or source code modification. </li>
 <li>The EJB specification that governs the use of enterprise beans is compatible
 with other Java™ APIs and CORBA. It also provides for interoperability
 between enterprise beans and non-Java applications.</li>
 </ul>
 <dl><dt class="dlterm"><b>Enterprise beans</b></dt>
 <dd>An <em>enterprise bean</em> is a non-visual component of a distributed,
 transaction-oriented enterprise application. Enterprise beans are typically
 deployed in EJB containers and run on EJB servers. You can customize them
 by changing their deployment descriptors and you can assemble them with other
 beans to create new applications. There are three types of enterprise beans: <em>session
 beans</em>, <em>entity beans</em>, and <em>message-driven</em> beans.<div class="p"><blockquote> <ul><li><b>Session beans</b>: <em>Session beans</em> are non-persistent
 enterprise beans. They can be stateful or stateless. A <em>stateful session
 bean</em> acts on behalf of a single client and maintains client-specific session
 information (called conversational state) across multiple method calls and
 transactions. It exists for the duration of a single client/server session.
 A <em>stateless session bean</em>, by comparison, does not maintain any conversational
 state. Stateless session beans are pooled by their container to handle multiple
 requests from multiple clients.</li>
 <li><b>Entity beans</b>: <em>Entity beans</em> are enterprise
 beans that contain persistent data and that can be saved in various persistent
 data stores. Each entity bean carries its own identity. Entity beans that
 manage their own persistence are called <em>bean-managed persistence (BMP)
  entity beans</em>. Entity beans that delegate their persistence to their EJB
 container are called <em>container-managed persistence (CMP) entity beans</em>.</li>
 <li><b>Message-driven beans</b>: <em>Message-driven beans</em> are
 enterprise beans that receive and process JMS messages. Unlike session or
 entity beans, message-driven beans have no interfaces. They can be accessed
 only through messaging and they do not maintain any conversational state.
  Message-driven beans allow asynchronous communication between the queue and
 the listener, and provide separation between message processing and business
 logic.</li>
 </ul>
 </blockquote>
 </div>
 </dd>
 </dl>
 <dl><dt class="dlterm"><b>Remote client view</b></dt>
 <dd>The <em>remote client view</em> specification became available beginning
 with EJB 1.1. The remote client view of an enterprise bean is location independent.
 A client running in the same JVM as a bean instance uses the same API to access
 the bean as a client running in a different JVM on the same or different machine.<ul><li><b>Remote interface</b>: The <em>remote interface</em> specifies
 the remote business methods that a client can call on an enterprise bean.</li>
 <li><b>Remote home interface</b>: The <em>remote home interface</em> specifies
 the methods used by remote clients for locating, creating, and removing instances
 of enterprise bean classes.</li>
 </ul>
 </dd>
 </dl>
 <dl><dt class="dlterm"><b>Local client view</b></dt>
 <dd>The <em>local client view</em> specification is available in EJB 2.0 or
 later. Unlike the remote client view, the local client view of a bean is location
 dependent. Local client view access to an enterprise bean requires both the
 local client and the enterprise bean that provides the local client view to
 be in the same JVM. The local client view therefore does not provide the location
 transparency provided by the remote client view. Local interfaces and local
 home interfaces provide support for lightweight access from enterprise bean
 that are local clients. Session and entity beans can be tightly couple with
 their clients, allowing access without the overhead typically associated with
 remote method calls.<ul><li><b>Local interface</b>: The <em>local interface</em> is
 a lightweight version of the remote interface, but for local clients. It includes
 business logic methods that can be called by a local client.</li>
 <li><b>Local home interface</b>: The <em>local home interface</em> specifies
 the methods used by local clients for locating, creating, and removing instances
 of enterprise bean classes.</li>
 </ul>
 </dd>
 </dl>
 <dl>
 <dt class="dlterm"><b>Web service client view</b></dt>
 <dd>In the EJB 2.1 specification, the EJB architecture introduced the support
 for Web services. A client for a session bean can be a Web service client.
 A Web service client can make use of the Web service client view of a stateless
 session bean, which has a corresponding service endpoint interface.<ul><li><b>Service endpoint interface: </b>
 The <em>service endpoint interface</em> for a stateless session bean exposes
 the functionality of the session bean as a Web service endpoint. The Web Service
 Description Language (WSDL) document for a Web service describes the Web service
 as a set of endpoints operating on messages. A WSDL document can include the
 service endpoint interface of a stateless session bean as one of its endpoints.
 An existing stateless session bean can be modified to include a Web service
 client view, or a service endpoint interface can be mapped from an existing
 WSDL to provide the correct interface.<p>A Web service client view is independent
 of location and can be accessed through remote calls.</p></li></ul>


 </dd>
 </dl>
 <dl><dt class="dlterm"><b>EJB client JAR file</b></dt>
 <dd>An EJB client JAR file is an optional JAR file that can contain the client
 interfaces that a client program needs to use the client views of the enterprise
 beans that are contained in the EJB JAR file. If you decide not to create
 an EJB client JAR file for an EJB module, all of the client interface classes
 will be in the EJB JAR file. By default, the workbench creates EJB client
 JAR projects for each corresponding EJB project.</dd>
 </dl>
 <dl><dt class="dlterm"><b>EJB container</b></dt>
 <dd>An <em>EJB container</em> is a runtime environment that manages one or more
 enterprise beans. The EJB container manages the life cycles of enterprise
 bean objects, coordinates distributed transactions, and implements object
 security. Generally, each EJB container is provided by an EJB server and contains
 a set of enterprise beans that run on the server.</dd></dl>
 <dl>

 <dt class="dlterm"><b>Deployment descriptor</b></dt>
 <dd>A <em>deployment descriptor</em> is an XML file packaged with the enterprise
 beans in an EJB JAR file or an EAR file. It contains metadata describing the
 contents and structure of the enterprise beans, and runtime transaction and
 security information for the EJB container.</dd></dl>
 <dl>
 <dt class="dlterm"><b>EJB server</b></dt>

 <dd>An <em>EJB server</em> is a high-level process or application that provides
 a runtime environment to support the execution of server applications that
 use enterprise beans. An EJB server provides a JNDI-accessible naming service,
 manages and coordinates the allocation of resources to client applications,
 provides access to system resources, and provides a transaction service. An
 EJB server could be provided by, for example, a database or application server.</dd>
 </dl>
 </div>
 <p>
 		(C) Copyright IBM Corporation 2000, 2005. All Rights Reserved.
 		</p>
 </body>
 </html>
	<?xml version="1.0" encoding="UTF-8"?>
	<!DOCTYPE html
	PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
	<html lang="en-us" xml:lang="en-us">
	<head>
	<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
	<!-- /*******************************************************************************
	* Copyright (c) 2000, 2005 IBM Corporation and others.
	* All rights reserved. This program and the accompanying materials
	* are made available under the terms of the Eclipse Public License v1.0
	* which accompanies this distribution, and is available at
	* http://www.eclipse.org/legal/epl-v10.html
	*
	* Contributors:
	* IBM Corporation - initial API and implementation
	*******************************************************************************/ -->
	<link rel="stylesheet" type="text/css" href="../../org.eclipse.wst.doc.user/common.css" />
	<title>EJB architecture</title>
	</head>
	<body id="cearch"><a name="cearch"><!-- --></a>

	<h1 class="topictitle1">EJB architecture</h1>
	<div><p>This topic provides a high-level overview of the distributed component
	architecture defined in the Sun Microsystems Enterprise JavaBeans™ (EJB)
	architecture specification.</p>
	<p>The complete Enterprise JavaBeans specifications and descriptions
	of the technology are available from the <a href="http://java.sun.com/products/ejb/docs.html#specs" target="_blank">java.sun.com</a> Web site.</p>
	<p>Enterprise beans provide several benefits for application developers: </p>
	<ul><li>They allow you to build distributed applications by combining components
	developed using tools from different vendors. </li>
	<li>They make it easy to write applications. You do not have to deal with
	low-level details of transaction and state management, multithreading, resource
	pooling, and other complex low-level APIs. However, if necessary, expert programmers
	can still gain direct access to the low-level APIs.</li>
	<li>They can be developed once and then deployed on multiple platforms without
	recompilation or source code modification. </li>
	<li>The EJB specification that governs the use of enterprise beans is compatible
	with other Java™ APIs and CORBA. It also provides for interoperability
	between enterprise beans and non-Java applications.</li>
	</ul>
	<dl><dt class="dlterm"><b>Enterprise beans</b></dt>
	<dd>An <em>enterprise bean</em> is a non-visual component of a distributed,
	transaction-oriented enterprise application. Enterprise beans are typically
	deployed in EJB containers and run on EJB servers. You can customize them
	by changing their deployment descriptors and you can assemble them with other
	beans to create new applications. There are three types of enterprise beans: <em>session
	beans</em>, <em>entity beans</em>, and <em>message-driven</em> beans.<div class="p"><blockquote> <ul><li><b>Session beans</b>: <em>Session beans</em> are non-persistent
	enterprise beans. They can be stateful or stateless. A <em>stateful session
	bean</em> acts on behalf of a single client and maintains client-specific session
	information (called conversational state) across multiple method calls and
	transactions. It exists for the duration of a single client/server session.
	A <em>stateless session bean</em>, by comparison, does not maintain any conversational
	state. Stateless session beans are pooled by their container to handle multiple
	requests from multiple clients.</li>
	<li><b>Entity beans</b>: <em>Entity beans</em> are enterprise
	beans that contain persistent data and that can be saved in various persistent
	data stores. Each entity bean carries its own identity. Entity beans that
	manage their own persistence are called <em>bean-managed persistence (BMP)
	entity beans</em>. Entity beans that delegate their persistence to their EJB
	container are called <em>container-managed persistence (CMP) entity beans</em>.</li>
	<li><b>Message-driven beans</b>: <em>Message-driven beans</em> are
	enterprise beans that receive and process JMS messages. Unlike session or
	entity beans, message-driven beans have no interfaces. They can be accessed
	only through messaging and they do not maintain any conversational state.
	Message-driven beans allow asynchronous communication between the queue and
	the listener, and provide separation between message processing and business
	logic.</li>
	</ul>
	</blockquote>
	</div>
	</dd>
	</dl>
	<dl><dt class="dlterm"><b>Remote client view</b></dt>
	<dd>The <em>remote client view</em> specification became available beginning
	with EJB 1.1. The remote client view of an enterprise bean is location independent.
	A client running in the same JVM as a bean instance uses the same API to access
	the bean as a client running in a different JVM on the same or different machine.<ul><li><b>Remote interface</b>: The <em>remote interface</em> specifies
	the remote business methods that a client can call on an enterprise bean.</li>
	<li><b>Remote home interface</b>: The <em>remote home interface</em> specifies
	the methods used by remote clients for locating, creating, and removing instances
	of enterprise bean classes.</li>
	</ul>
	</dd>
	</dl>
	<dl><dt class="dlterm"><b>Local client view</b></dt>
	<dd>The <em>local client view</em> specification is available in EJB 2.0 or
	later. Unlike the remote client view, the local client view of a bean is location
	dependent. Local client view access to an enterprise bean requires both the
	local client and the enterprise bean that provides the local client view to
	be in the same JVM. The local client view therefore does not provide the location
	transparency provided by the remote client view. Local interfaces and local
	home interfaces provide support for lightweight access from enterprise bean
	that are local clients. Session and entity beans can be tightly couple with
	their clients, allowing access without the overhead typically associated with
	remote method calls.<ul><li><b>Local interface</b>: The <em>local interface</em> is
	a lightweight version of the remote interface, but for local clients. It includes
	business logic methods that can be called by a local client.</li>
	<li><b>Local home interface</b>: The <em>local home interface</em> specifies
	the methods used by local clients for locating, creating, and removing instances
	of enterprise bean classes.</li>
	</ul>
	</dd>
	</dl>
	<dl>
	<dt class="dlterm"><b>Web service client view</b></dt>
	<dd>In the EJB 2.1 specification, the EJB architecture introduced the support
	for Web services. A client for a session bean can be a Web service client.
	A Web service client can make use of the Web service client view of a stateless
	session bean, which has a corresponding service endpoint interface.<ul><li><b>Service endpoint interface: </b>
	The <em>service endpoint interface</em> for a stateless session bean exposes
	the functionality of the session bean as a Web service endpoint. The Web Service
	Description Language (WSDL) document for a Web service describes the Web service
	as a set of endpoints operating on messages. A WSDL document can include the
	service endpoint interface of a stateless session bean as one of its endpoints.
	An existing stateless session bean can be modified to include a Web service
	client view, or a service endpoint interface can be mapped from an existing
	WSDL to provide the correct interface.<p>A Web service client view is independent
	of location and can be accessed through remote calls.</p></li></ul>


	</dd>
	</dl>
	<dl><dt class="dlterm"><b>EJB client JAR file</b></dt>
	<dd>An EJB client JAR file is an optional JAR file that can contain the client
	interfaces that a client program needs to use the client views of the enterprise
	beans that are contained in the EJB JAR file. If you decide not to create
	an EJB client JAR file for an EJB module, all of the client interface classes
	will be in the EJB JAR file. By default, the workbench creates EJB client
	JAR projects for each corresponding EJB project.</dd>
	</dl>
	<dl><dt class="dlterm"><b>EJB container</b></dt>
	<dd>An <em>EJB container</em> is a runtime environment that manages one or more
	enterprise beans. The EJB container manages the life cycles of enterprise
	bean objects, coordinates distributed transactions, and implements object
	security. Generally, each EJB container is provided by an EJB server and contains
	a set of enterprise beans that run on the server.</dd></dl>
	<dl>

	<dt class="dlterm"><b>Deployment descriptor</b></dt>
	<dd>A <em>deployment descriptor</em> is an XML file packaged with the enterprise
	beans in an EJB JAR file or an EAR file. It contains metadata describing the
	contents and structure of the enterprise beans, and runtime transaction and
	security information for the EJB container.</dd></dl>
	<dl>
	<dt class="dlterm"><b>EJB server</b></dt>

	<dd>An <em>EJB server</em> is a high-level process or application that provides
	a runtime environment to support the execution of server applications that
	use enterprise beans. An EJB server provides a JNDI-accessible naming service,
	manages and coordinates the allocation of resources to client applications,
	provides access to system resources, and provides a transaction service. An
	EJB server could be provided by, for example, a database or application server.</dd>
	</dl>
	</div>
	<p>
	(C) Copyright IBM Corporation 2000, 2005. All Rights Reserved.
	</p>
	</body>
	</html>