EJB工作原理学习笔记

EJB工作原理学习笔记 1 RMI工作原理 2 websphere实现 3 weblogic实现 4 理解体会 1：RMI工作原理 首先说说RMI的工作原理，因为EJB毕竟是基于RMI的嘛。废话就不多讲了，RMI的本质就是实现在不同JVM之间的 调用 它的实现方法就是在两个JVM中各开一个Stub和Skeleton，二者通过socket通信来实现参数和返回值的传递。 有关RMI的例子代码网上可以找到不少，但绝大部分都是通过extend the interface java.rmi.Remote实现，已 经封装的很完善了，不免使人有雾里看花的感觉。下面的例子是我在《Enterprise JavaBeans》里看到的，虽 然很粗糙，但很直观，利于很快了解它的工作原理。 1. 定义一个Person的接口，其中有两个business method, getAge() 和getName() 代码: public interface Person {     public int getAge() throws Throwable;     public String getName() throws Throwable; }   2. Person的实现PersonServer类 代码: public class PersonServer implements Person {     int age;     String name;     public PersonServer(String name, int age) {         this.age = age;         this.name = name;     }     public int getAge() {         return age;     }     public String getName() {         return name;     } }   3. 好，我们现在要在Client机器上调用getAge()和getName()这两个business method，那么就得编写相应的Stub(Client端)和Skeleton(Server端)程序。这是Stub的实现： 代码: import java.io.ObjectOutputStream; import java.io.ObjectInputStream; import java.net.Socket; public class Person_Stub implements Person {     Socket socket;     public Person_Stub() throws Throwable {         // connect to skeleton         socket = new Socket("computer_name", 9000);     }     public int getAge() throws Throwable {         // pass method name to skeleton         ObjectOutputStream outStream =             new ObjectOutputStream(socket.getOutputStream());         outStream.writeObject("age");         outStream.flush();         ObjectInputStream inStream =             new ObjectInputStream(socket.getInputStream());         return inStream.readInt();     }     public String getName() throws Throwable {         // pass method name to skeleton         ObjectOutputStream outStream =             new ObjectOutputStream(socket.getOutputStream());

        outStream.writeObject("name");
        outStream.flush();

        ObjectInputStream inStream =
            new ObjectInputStream(socket.getInputStream());
        return (String)inStream.readObject();
    }
}
 

注意，Person_Stub和PersonServer一样，都implements

Person。它们都实现了getAge()和getName()两个business

method，不同的是PersonServer是真的实现，Person_Stub是建立socket连接，并向Skeleton发请求，然后通过

Skeleton调用PersonServer的方法，最后接收返回的结果。

4. Skeleton实现
代码:

import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.net.Socket;
import java.net.ServerSocket;

public class Person_Skeleton extends Thread {
    PersonServer myServer;

    public Person_Skeleton(PersonServer server) {
        // get reference of object server
        this.myServer = server;
    }

    public void run() {
        try {
            // new socket at port 9000
            ServerSocket serverSocket = new ServerSocket(9000);
            // accept stub's request
            Socket socket = serverSocket.accept();

            while (socket != null) {
                // get stub's request
                ObjectInputStream inStream =
                    new ObjectInputStream(socket.getInputStream());
                String method = (String)inStream.readObject();

                // check method name
                if (method.equals("age")) {
                    // execute object server's business method
                    int age = myServer.getAge();
                    ObjectOutputStream outStream =
                        new ObjectOutputStream(socket.getOutputStream());

 

                    // return result to stub
                    outStream.writeInt(age);
                    outStream.flush();
                }

                if(method.equals("name")) {
                    // execute object server's business method
                    String name = myServer.getName();
                    ObjectOutputStream outStream =
                        new ObjectOutputStream(socket.getOutputStream());

                    // return result to stub
                    outStream.writeObject(name);
                    outStream.flush();
                }
            }
        } catch(Throwable t) {
            t.printStackTrace();
            System.exit(0);
        }
    }

    public static void main(String args []) {
        // new object server
        PersonServer person = new PersonServer("Richard", 34);

        Person_Skeleton skel = new Person_Skeleton(person);
        skel.start();
    }
}
 

Skeleton类 extends from Thread，它长驻在后台运行，随时接收client发过来的request。并根据发送过来的

key去调用相应的business method。

5. 最后一个，Client的实现
代码:

public class PersonClient {
    public static void main(String [] args) {
        try {
            Person person = new Person_Stub();
            int age = person.getAge();