EJB

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EJB

1.EJB(企业级javaBean)——是bean组件；用于实现业务的分离(进程的分布式)；底层是socket机制。

2.EJB的分类

2.1：SessionBean——用于问答式会话，专人负责

2.1.1：stateless——不保存会话状态，所有客户都共用一个EJB

×应用——登录验证、完成单一算法

2.1.2：stateful——有会话状态，对于每个客户都产生一个EJB

×实现“购物车”功能，跟踪客户的流程

2.2：EntityBean——与数据库实体打交道

2.2.1：CMP——简单，方便，效率低；由容器自动完成

2.2.2:BMP——编写难，效率高；由程序员编写

2.3：MessageDriverBean——批量信息异步处理

3.EJB发展

3.1：通过socket来实现不同进程间的信息通讯，客户端需要服务器里的类信息——容易泄露代码

3.2：为服务器端提供接口，将接发送给客户端，避免了代码泄露——传参复杂

3.3：在服务器端书写引用名和类、方法对应的配置文件，只传引用名。——JNDI (Java命名与目录接口)

3.4：RMI

3.5：容器

4.EJB的第三方插件

4.1：Jboss——Jboss中，客户端是端口1099，web服务是端口8080

4.2：WebLogic

4.3：WebSpare

5.EJB代码

5.1：Home interface ——创建EJB实例，提供生命周期管理方法。

Java代码

//第一步：书写继承javax.ejb.EJBHome接口的接口

package com.lovo.stateless;

import java.rmi.RemoteException;

import javax.ejb.CreateException;

import javax.ejb.EJBHome;//必须继承该接口

public interface MyStatelessHome extends EJBHome{

//create方法返回远程接口类型且抛出CreateException异常

public MyStatelessRemote create() throws CreateException,RemoteException;

//所有的方法都需要跑RemoteException异常

}

//第一步：书写继承javax.ejb.EJBHome接口的接口

package com.lovo.stateless;

import java.rmi.RemoteException;

import javax.ejb.CreateException;

import javax.ejb.EJBHome;//必须继承该接口

public interface MyStatelessHome extends EJBHome{

//create方法返回远程接口类型且抛出CreateException异常

public MyStatelessRemote create() throws CreateException,RemoteException;

//所有的方法都需要跑RemoteException异常

}

5.2：Remote interface——定义业务方法和辅助方法

Java代码

//第二步：书写继承接口java.rmi.RemoteException的接口

package com.lovo.stateless;

import java.rmi.RemoteException;

import javax.ejb.EJBObject;//必须继承该接口

public interface MyStatelessRemote extends EJBObject{

//所有的方法必须抛RemoteException

public String sayHelloWorld(String name) throws RemoteException;

public String sayGoodBye(String name) throws RemoteException;

}

//第二步：书写继承接口java.rmi.RemoteException的接口

package com.lovo.stateless;

import java.rmi.RemoteException;

import javax.ejb.EJBObject;//必须继承该接口

public interface MyStatelessRemote extends EJBObject{

//所有的方法必须抛RemoteException

public String sayHelloWorld(String name) throws RemoteException;

public String sayGoodBye(String name) throws RemoteException;

}

5.3：Bean class——实现2个接口的方法和自己的业务方法

Java代码

//第三步：书写实现接口的EJB类

package com.lovo.stateless;

import java.rmi.RemoteException;

import javax.ejb.EJBException;

import javax.ejb.SessionBean;

//必须继承该接口，并实现回调方法：激活、钝化、移除设置会话文档

import javax.ejb.SessionContext;

/**

* XDoclet-based session bean. The class must be declared public according to

* the EJB specification.

* To generate the EJB related files to this EJB: - Add Standard EJB module to

* XDoclet project properties - Customize XDoclet configuration for your

* appserver - Run XDoclet

* Below are the xdoclet-related tags needed for this EJB.

* @ejb.bean name="MyStateless" display-name="Name for MyStateless"

* description="Description for MyStateless"

* jndi-name="ejb/MyStateless" type="Stateless" view-type="remote"

//类必须是public的

public class MyStatelessBean implements SessionBean {

/** The session context */

private SessionContext context;

//必须有一个无参构造方法

public MyStatelessBean() {

// TODO Auto-generated constructor stub

}

// 创建——根据主接口中create方法的参数和个数创建EJB

public void ejbCreate() throws EJBException, RemoteException {

}

// 激活——将代码从硬盘中提取到硬盘。

public void ejbActivate() throws EJBException, RemoteException {

// TODO Auto-generated method stub

}

// 钝化——将长时间不用的代码从内存中移动到EJB所在的硬盘。

public void ejbPassivate() throws EJBException, RemoteException {

// TODO Auto-generated method stub

}

// 移除——清楚EJB的所有信息。

public void ejbRemove() throws EJBException, RemoteException {

// TODO Auto-generated method stub

}

/**

* Set the associated session context. The container calls this method after

* the instance creation.

* The enterprise bean instance should store the reference to the context

* object in an instance variable.

* This method is called with no transaction context.

* @throws EJBException

* Thrown if method fails due to system-level error.

public void setSessionContext(SessionContext newContext)

throws EJBException {

context = newContext;

}

// 必须实现远程接口中定义的每个方法

public String sayHelloWorld(String name) throws RemoteException {

return name + "说：大家好，我是清晨！";

}

public String sayGoodBye(String name) throws RemoteException{

return name + "说：再见了，飞扬的青春！";

}

//第三步：书写实现接口的EJB类

package com.lovo.stateless;

import java.rmi.RemoteException;

import javax.ejb.EJBException;

import javax.ejb.SessionBean;

//必须继承该接口，并实现回调方法：激活、钝化、移除设置会话文档

import javax.ejb.SessionContext;

/**

* XDoclet-based session bean. The class must be declared public according to

* the EJB specification.

* To generate the EJB related files to this EJB: - Add Standard EJB module to

* XDoclet project properties - Customize XDoclet configuration for your

* appserver - Run XDoclet

* Below are the xdoclet-related tags needed for this EJB.

* @ejb.bean name="MyStateless" display-name="Name for MyStateless"

* description="Description for MyStateless"

* jndi-name="ejb/MyStateless" type="Stateless" view-type="remote"

//类必须是public的

public class MyStatelessBean implements SessionBean {

/** The session context */

private SessionContext context;

//必须有一个无参构造方法

public MyStatelessBean() {

// TODO Auto-generated constructor stub

}

// 创建——根据主接口中create方法的参数和个数创建EJB

public void ejbCreate() throws EJBException, RemoteException {

}

// 激活——将代码从硬盘中提取到硬盘。

public void ejbActivate() throws EJBException, RemoteException {

// TODO Auto-generated method stub

}

// 钝化——将长时间不用的代码从内存中移动到EJB所在的硬盘。

public void ejbPassivate() throws EJBException, RemoteException {

// TODO Auto-generated method stub

}

// 移除——清楚EJB的所有信息。

public void ejbRemove() throws EJBException, RemoteException {

// TODO Auto-generated method stub

}

/**

* Set the associated session context. The container calls this method after

* the instance creation.

* The enterprise bean instance should store the reference to the context

* object in an instance variable.

* This method is called with no transaction context.

* @throws EJBException

* Thrown if method fails due to system-level error.

public void setSessionContext(SessionContext newContext)

throws EJBException {

context = newContext;

}

//必须实现远程接口中定义的每个方法

public String sayHelloWorld(String name) throws RemoteException {

return name + "说：大家好，我是清晨！";

}

public String sayGoodBye(String name) throws RemoteException{

return name + "说：再见了，飞扬的青春！";

}

5.4:配置文件

Ejb-jar.xml代码

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd" >

<ejb-jar>

<enterprise-beans>

<ejb-name>test67stateless</ejb-name>

<home>com.lovo.stateless.MyStatelessHome</home>

<remote>com.lovo.stateless.MyStatelessRemote</remote>

<ejb-class>com.lovo.stateless.MyStatelessBean</ejb-class>

<session-type>Stateless</session-type>

<transaction-type>Container</transaction-type>

</session>

<ejb-name>test67stateful</ejb-name>

<home>com.lovo.stateful.MyStatefulHome</home>

<remote>com.lovo.stateful.MyStatefulRemote</remote>

<ejb-class>com.lovo.stateful.MyStatefulBean</ejb-class>

<session-type>Stateful</session-type>

<transaction-type>Container</transaction-type>

</session>

</enterprise-beans>

</ejb-jar>