Servlet传送对象给Applet使用

一起学习

前日,一位朋友与我谈论Servlet与Applet共享Java对象的问题,现发表出来与大家分享,文中瑕癖
之处甚多,望各位指教.
朋友谈论的需求是这样的:他想通过页面上一个Applet呼叫一个服务器Servlet,而从Servlet产生
一个Java对象再传给另外一个Applet,怎么样让Servlet实时地把对象传给Applet这是一个问题,有一个方
案是采用JMS(JavaMessageService),在我以后的文章中会有叙述的.这里我给大家展示一个简单的实现,那
就是让Applet主动访问Servlet,让Servlet返回Java对象.下面给出全部代码和配置,其中Applet部分涵盖
了Javascript与Applet的互相调用,对于该部分不感兴趣的朋友可以复略.

第一步,编写需要传递的对象类
/**
 * Class Person just a demo for translate this class to client
 * @author:  rookie
 * @datetime: 2002-7-26
 */
package exapplet;
import java.io.*;


public class Person implements Serializable {//必须实现Serializable接口才能序列化
 private String m_Name;
 private int  m_Age;

 public Person() {
  this("",0);
 }
 public Person(String name,int age) {
  this.m_Name = name;
  this.m_Age = age;
 }
 public String getName() {
  return m_Name;
 }
 public int getAge() {
  return m_Age;
 }

 //Serializable接口中声明的方法
 private void writeObject(java.io.ObjectOutputStream out) 
     throws IOException {
  out.defaultWriteObject();
 }

 //Serializable接口中声明的方法 
 private void readObject(java.io.ObjectInputStream in)
     throws IOException, ClassNotFoundException {
  in.defaultReadObject();
 } 

 public static void main(String[] args) {
  try {
   Person p = new Person("Liaoyuan",25);
   ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(new File("test.obj")));
   oos.writeObject(p);
   oos.close();
   ObjectInputStream ois = new ObjectInputStream (new FileInputStream(new File("test.obj")));
   Person q = (Person)ois.readObject();
   ois.close();
   System.out.println(q.getName());
   System.out.println(q.getAge());
  } catch(Exception exp) {
   exp.printStackTrace();
  }
 }
}


第二步,实现Servlet
package exapplet;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class MyServlet extends HttpServlet 
{
 public void doGet(HttpServletRequest req,HttpServletResponse res)
  throws ServletException,IOException
 {
  String fPath = "H:\\XSchool\\WorkingRoom\\exapplet\\src\\java.obj";
  
  String act = req.getParameter("Action");
  if ( act.equals("UpdateObject") ) {
   //创建更新JavaObject
   Person p = new Person("Liaoyuan",26);
   ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(new File(fPath)));
   oos.writeObject(p);
   oos.close();
   DataOutputStream dos = new DataOutputStream(res.getOutputStream());
   dos.writeBytes("Server Java Object Updated OK!");
   dos.close();
  } else if ( act.equals("GetObject") ) {
   //传回对象给Applet
   res.setContentType("application/octet-stream");
   Person p;
   ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File(fPath)));
   try {
    p    = (Person)ois.readObject();
   } catch (ClassNotFoundException e) {
    p = new Person();
   }
   ois.close();
   
   ObjectOutputStream oos = new ObjectOutputStream(res.getOutputStream());
   oos.writeObject(p);
   oos.close();
  }
 }
 public String getServletInfo()
 {
  return "A simple Servlet!";
 }
}


第三步,实现呼叫Servlet更新对象的Applet
package exapplet;
import java.awt.*;
import java.applet.*;
import java.io.*;
import java.net.*;
import netscape.javascript.*;

public class MyApplet extends java.applet.Applet
{
 public void init()
 {
 }
 public void paint(Graphics g)
 {}

 //This method will be call in html
 public void invoke() {
  try {
   URL url = new URL("");
   URLConnection urlcon = url.openConnection();
   urlcon.connect();
   
   DataInputStream dis=new DataInputStream(urlcon.getInputStream());
   String txt = dis.readLine();
   dis.close();
   
   String[] info = new String[]{txt};
   JSObject.getWindow(this).call("alert",info);
  } catch (Exception e) {
  }
 }
}


第四步,实现提取对象的Applet
package exapplet;
import java.awt.*;
import java.applet.*;
import java.io.*;
import java.net.*;
import netscape.javascript.*;

public class MyAppletB extends java.applet.Applet
{
 public void init()
 {
 }
 public void paint(Graphics g)
 {}

 //This method will be call in html
 public void invoke() {
  try {
   URL url = new URL("");
   URLConnection urlcon = url.openConnection();
   urlcon.connect();
   ObjectInputStream ois=new ObjectInputStream(urlcon.getInputStream());
   Person p = (Person)ois.readObject();
   ois.close();
   String[] info = new String[]{"Person Info\n\n-Name: " p.getName() "\n-Age : " p.getAge()};
   JSObject.getWindow(this).call("alert",info);
  } catch (Exception e) {
  }
 }
}

第五步,配制WebServer(我用的是Tomcat4.0)
拷贝编译后的MyServlet.class到相应目录下,
编辑对应的web.xml文件,确保下面的内容正确



 
        PostToApplet
        exapplet.MyServlet
    

 
        
            PostToApplet
        
        
            /exapplet/PostToApplet
        
    


第六步,编写html文件
呼叫更新的html






Hello This is a Test!








提取对象的html






Hello This is a Test!

中间有错误的地方请指教,[e-mail]

下载本文示例代码


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