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Beans入门必读之状态会话Bean基础

王朝other·作者佚名  2008-05-19
窄屏简体版  字體: |||超大  

Stateful Session Bean可以一对一的维持某个调用客户的状态,并且在不同的方法调用中维持这个状态, 由于对于每一个并发用户,必须有一个对应的Stateful Session Bean,为了提高系统的效率,Stateful Session Bean可以在一定的客户空闲时间后被写入二级存储设备(如硬盘),在客户发出新的调用请求后,再从二级存储 设备恢复到内存中。但是在多用户下,Stateless Session Bean运行效率高于Stateful Session Bean。

javax.ejb.EnterpriseBean接口继承了java.io.Serializable,用以实现写入读出操作。

当EJB容器调用ejbPassivate()方法钝化了bean之后,就可以把它写入二级存储设备,然后容器调用ejbActivate()方法激活bean,把它从二级存储设备中读出。

状态bean的钝化过程

计数bean的远程接口

远程接口定义了一个业务方法count(),它将在企业bean类中实现。

激活状态bean

package com.wiley.compBooks.roman.session.count;

import javax.ejb.*;

import java.rmi.RemoteException;

/**

* These are CountBean's business logic methods.

*

* This interface is what clients operate on when they

* interact with EJB objects. The container vendor will

implement this interface; the implemented object is

* the EJB Object, which delegates invocations to the

* actual bean.

*/

public interface Count extends EJBObject {

/**

* Increments the int stored as conversational state

*/

public int count() throws RemoteException;

}

Source Count.java

package com.wiley.compBooks.roman.session.count;

import javax.ejb.*;

/**

* Demonstration Stateful Session Bean. This bean is

* initialized to some integer value and has a business

* method that increments the value.

*

* This example shows the basics of how to write a stateful

* session bean and how passivation/activation works.

*/

public class CountBean implements SessionBean {

private SessionContext ctx;

// The current counter is our conversational state.

public int val;

//

// Business methods

//

/**

* Counts up

*/

public int count() {

System.out.println("count()");

return ++val;

}

//

// EJB-required methods

//

public void ejbCreate(int val) throws CreateException {

this.val = val;

System.out.println("ejbCreate()");

}

public void ejbRemove() {

System.out.println("ejbRemove()");

}

public void ejbActivate() {

System.out.println("ejbActivate()");

}

public void ejbPassivate() {

System.out.println("ejbPassivate()");

}

public void setSessionContext(SessionContext ctx) {

}

}

Source CountBean.java

Bean实现了javax.ejb.SessionBean。所以,它必须定义所有SessionBean定义的方法。

OjbCreate()初始化带了val的参数。它将作为counter的初始状态。在钝化和激活bean的过程中,val变量被保护。

计数bean的home接口

package com.wiley.compBooks.roman.session.count;

import javax.ejb.*;

import java.rmi.RemoteException;

/**

* This is the home interface for CountBean. This interface

* is implemented by the EJB Server's glue-code tools - the

* implemented object is called the Home Object and serves

* as a factory for EJB Objects.

*

* One create() method is in this Home Interface, which

* corresponds to the ejbCreate() method in the CountBean file.

*/

public interface CountHome extends EJBHome {

/*

* This method creates the EJB Object.

*

* @param val Value to initialize counter to

*

* @return The newly created EJB Object.

*/

Count create(int val) throws RemoteException, CreateException;

}

Source CountHome.java.

计数bean的配置描述符

计数bean的配置描述符

计数bean的环境属性

生成计数bean的Ejb-jar文件

计数bean的客户端代码

package com.wiley.compBooks.roman.session.count;

import javax.ejb.*;

import javax.naming.*;

import java.util.Properties;

/**

* This class is a simple example of client code that invokes

* methods on a simple Stateless Enterprise Bean.

*

* We create 3 EJB Objects in this example, but we allow

* the container to have only 2 in memory. This illustrates how

* beans are passivated to storage.

*/

public class CountClient {

public static void main(String[] args) {

try {

/*

* Get System properties for JNDI initialization

*/

Properties props = System.getProperties();

/*

* Get a reference to the Home Object - the

* factory for EJB Objects

*/

Source CountClient.java

1、需要JNDL初始化上下文

2、使用JNDL定位home接口

3、使用home对象建立3个不同的计数EJB对象,因此也就和三个不同的客户端建立了会话

4、配置描述符限制了同时只能有两个bean工作,因此3个bean中一定有钝化的。在调用ejbPassivate()时,打印一条信息。

5、在每个EJB对象上调用count()方法,调用ejbActivate()方法激活bean,该方法打印一条信息。

6、最后所有的EJB对象被删除。

package com.wiley.compBooks.roman.session.count;

import javax.ejb.*;

import javax.naming.*;

import java.util.Properties;

/**

* This class is a simple example of client code that invokes

* methods on a simple Stateless Enterprise Bean.

*

* We create 3 EJB Objects in this example, but we allow

* the container to have only 2 in memory. This illustrates how

* beans are passivated to storage.

*/

public class CountClient {

public static void main(String[] args) {

try {

/*

* Get System properties for JNDI initialization

*/

Properties props = System.getProperties();

/*

* Get a reference to the Home Object - the

* factory for EJB Objects

*/

Context ctx = new InitialContext(props);

CountHome home = (CountHome) ctx.lookup("CountHome");

/*

* An array to hold 3 Count EJB Objects

*/

Count count[] = new Count[3];

int countVal = 0;

/*

* Create and count() on each member of array

*/

System.out.println("Instantiating beans...");

for (int i=0; i

/*

* Create an EJB Object and initialize

* it to the current count value.

*/

count[i] = home.create(countVal);

/*

* Add 1 and print

*/

countVal = count[i].count();

System.out.println(countVal);

/*

* Sleep for 1/2 second

*/

Thread.sleep(500);

}

/*

* Let's call count() on each EJB Object to

* make sure the beans were passivated and

* activated properly.

*/

System.out.println("Calling count() on beans...");

for (int i=0; i

/*

* Add 1 and print

*/

countVal = count[i].count();

System.out.println(countVal);

/*

* Sleep for 1/2 second

*/

Thread.sleep(500);

}

/*

* Done with EJB Objects, so remove them

*/

for (int i=0; i

count[i].remove();

}

} catch (Exception e) {

e.printStackTrace();

}

}

}

Source CountClient.java

运行客户端:

对于BEA的WebLogic,执行:

java -Djava.naming.factory.initial=

weblogic.jndi.TengahInitialContextFactory

-Djava.naming.provider.url=

t3://localhost:7001

com.wiley.compBooks.roman.session.count.CountClient

 
 
 
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