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ajax与java配合的学习（入门--ajax聊天器）总结

AjaxJava浏览器ServletJSP 
阅读更多
思想斗争了很久，终于开始接触ajax，作为一个初学者，模仿是个不错的学习方法，至少我是这么学过来的，站长巨人的肩膀上。

这次模仿的内容来自《基于J2EE的Ajax宝典》电子书，在此表示感谢。介绍的是Jsp页面聊天器和ajax聊前器的区别，及ajax的特点体现。

---相对于传统的JSP聊天室而言，Ajax聊天室的速度更快，响应更加流畅。对于复杂页面，Ajax的优势将更加明显：Ajax聊天室只需从服务器获取必须更新的聊天记录，而无须下载整个页面。
Ajax聊天室的最大特点是页面无须刷新，用户感觉不到页面的下载。使用Ajax聊天室时，用户感觉到仿佛在使用普通的Socket聊天室，因为聊天室的页面无须刷新，但用户的聊天信息实时更新。这一切都依赖于Ajax的异步发送请求和动态更新页面。

学习能力自称很强的我，在这下才知道是多么的渺小啊，花了整整一天的时间才得以实现，但这个过程虽败犹荣啊，更深刻的了解了ajax功能实现的整个流程。

1：创建XMLHttpRequest对象
2：取得与服务器的连接（用到post请求）
3：发送post请求时应该增加该文件头
4：指定当XMLHttpRequest状态变化时的处理函数（一个监听的过程）
5:发送请求，及发送信息

-1：这里就是步骤4中的处理函数的书写了


下面贴出ajax聊天器的代码（无数据库）
聊天器聊天界面代码： 
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'chat2.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
<script type="text/javascript">
var input;
var XMLHttpReq;
function createXMLHttpRequest()
{
input=document.getElementById("123");
 input.focus();

XMLHttpReq = new ActiveXObject("Msxml2.XMLHTTP");
var chatMsg=input.value;
var url = "Chat.do";
XMLHttpReq.open("post", url, true);
XMLHttpReq.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
XMLHttpReq.onreadystatechange = processResponse;
//发送请求后，将聊天信息的输入文本框清空
input.value="";
//发送请求，send的参数包含许多的key-value对
//即以“请求参数名=请求参数值”的形式发送请求参数
XMLHttpReq.send("chatMsg=" + chatMsg); // 发送请求

}

function sendEmptyRequest()
{
//创建XMLHttpRequest对象
if(window.XMLHttpRequest)
{
  XMLHttpReq=new XMLHttpRequest();
}
if (window.ActiveXObject)
{
try
{
//使用AcitveXObject函数创建浏览器
XMLHttpReq = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
//如果出现异常，再次尝试以如下方式创建XMLHttpRequest对象
try
{
XMLHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
}
catch (e)
{
  window.alert("internet");
}
}
}
//定义服务器响应的URL
var url = "Chat.do";
//建立与服务器的连接
XMLHttpReq.open("post", url, true);
//设置发送请求的参数格式
XMLHttpReq.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
//指定响应处理函数
XMLHttpReq.onreadystatechange = processResponse;
//发送请求
XMLHttpReq.send(null);
setTimeout("sendEmptyRequest()", 800);
}

function processResponse()
{
//如果服务器响应已经完成
if(XMLHttpReq.readyState == 4)
{
//判断对象状态，如果服务器生成了正常响应
if (XMLHttpReq.status == 200)
{
//信息已经成功返回，开始处理信息
//将聊天文本域的内容设置成聊天信息
document.getElementById("chatArea").value = XMLHttpReq.responseText;
}
else
{
//页面不正常
window.alert("您所请求的页面有异常。");
}
}
}

function enterHandler(event)
{
//定义键盘中发出事件的键
var keyCode=event.keyCode?event.keyCode:event.which?event.which:
event.charCode;//回车键的代码为13，如果按下了回车键
if (keyCode == 13)
{
createXMLHttpRequest();
}
}


</script>
  </head >
  
  <body onload="JavaScript:sendEmptyRequest();">
   <input type="button" onclick="JavaScript:createXMLHttpRequest();" value="clickme">
   
   <table width="780" border="1" align="center">
<tr>
<td><p align="center">聊天页面</p>
<!-- 下面定义聊天使用的文本域，该文本域用于显示当前聊天信息 -->

<p align="center">
<textarea id="chatArea" name="chatArea" cols="100" rows="30" readonly="readonly"></textarea>
</p>
<div align="center">
<!-- 下面是输入聊天信息所使用的文本，并为onKeyPress事件指定了监听函数 -->
<input id="123" name="chatMsg" type="text" size="90" onKeyPress="JavaScript:enterHandler(event);">
<!-- 下面是输入聊天信息的文本框，并为onclick事件指定了监听函数 -->
<input type="button" name="button" value="提交" onclick="JavaScript:createXMLHttpRequest();">
</div>
<p>&nbsp; </p>
</td>
</tr>
</table>
  </body>
</html>


有三个控制类处理类（servlet）
1：注册控制处理 
package com.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.method.ChatService;

public class RegServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String name=request.getParameter("username");
		String pass=request.getParameter("password");
		if(name==null||pass==null)
		{
			
				request.setAttribute("tip", "用户名和密码都不能为空");
				forward("/reg.jsp", request, response);
				}
				//开始调用业务逻辑对象的方法
				try
				{
				//调用业务逻辑对象的方法
				if (ChatService.instance().addUser(name, pass))
				{
				//如果注册成功，则将提示信息存入系统的tip属性
				request.setAttribute("tip", "注册成功，请登录系统");
				//将请求转发到reg.jsp页面显示
				forward("/reg.jsp", request, response);
				}
				else
				{
				//如果不能正常注册，则将提示信息放入request属性
				request.setAttribute("tip", "无法正常注册，请重试");
				forward("/reg.jsp", request, response);
				}
				}
				//如果捕捉到异常，例如注册的用户名已经存在
				catch (Exception e)
				{
				//将异常信息设置成request属性
				request.setAttribute("tip", e.getMessage());
				forward("/reg.jsp", request, response);
				}
		
	}
	
	
	private void forward(String url, HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException
			{
			ServletContext sc = getServletConfig().getServletContext();
			RequestDispatcher rd = sc.getRequestDispatcher(url);
			rd.forward(request, response);
			}

	/**
	 * Constructor of the object.
	 */
	public RegServlet() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out
				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.print("    This is ");
		out.print(this.getClass());
		out.println(", using the GET method");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out
				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.print("    This is ");
		out.print(this.getClass());
		out.println(", using the POST method");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
	}

}

2：登陆控制处理类： 
package com.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.method.ChatService;

public class LoginServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public LoginServlet() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out
				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.print("    This is ");
		out.print(this.getClass());
		out.println(", using the GET method");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out
				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.print("    This is ");
		out.print(this.getClass());
		out.println(", using the POST method");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
	}

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String name=request.getParameter("username");
		String pass=request.getParameter("password");
		if(ChatService.instance().validLogin(name, pass))
		{   request.getSession().setAttribute("username", name);
			String message=ChatService.instance().getMsg();
			request.setAttribute("message", message);
			forward("/chat2.jsp",request,response);
		}
		else
		{
			request.setAttribute("tip", "用户名和密码不匹配");
			forward("/login.jsp",request,response);
		}
		
	}
	private void forward(String url, HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException
			{
			ServletContext sc = getServletConfig().getServletContext();
			RequestDispatcher rd = sc.getRequestDispatcher(url);
			rd.forward(request, response);
			}
	
	

}

3：聊天控制处理类： 
package com.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.method.ChatService;

public class ChatServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public ChatServlet() {
		super();
	}

	/**
	 * Destruction of the servlet. <br>
	 */
	public void destroy() {
		super.destroy(); // Just puts "destroy" string in log
		// Put your code here
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out
				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.print("    This is ");
		out.print(this.getClass());
		out.println(", using the GET method");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html;charset=gbk");
		PrintWriter out = response.getWriter();
		out
				.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
		out.println("<HTML>");
		out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
		out.println("  <BODY>");
		out.print("    This is ");
		out.print(this.getClass());
		out.println(", using the GET method");
		out.println("  </BODY>");
		out.println("</HTML>");
		out.flush();
		out.close();

	}

	/**
	 * Initialization of the servlet. <br>
	 *
	 * @throws ServletException if an error occurs
	 */
	public void init() throws ServletException {
		// Put your code here
	}

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		String msg=request.getParameter("chatMsg");
		String user=(String) request.getSession().getAttribute("username");
		if(msg!=null)
		{
			ChatService.instance().addMsg(user, msg);
		}
		
//		String message=ChatService.instance().getMsg();
//		request.setAttribute("message", message);
//		forward("/chat.jsp",request,response);
		//设置中文输出流
		response.setContentType("text/html;charset=utf-8");
		//获取页面输出流
		PrintWriter out = response.getWriter();
		//将当前系统的聊天记录输出到页面
		out.println(ChatService.instance().getMsg());
	}
	private void forward(String url, HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException
			{
			ServletContext sc = getServletConfig().getServletContext();
			RequestDispatcher rd = sc.getRequestDispatcher(url);
			rd.forward(request, response);
			}
	
	

}


然后就是web.xml的配置了 
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>RegServlet</servlet-name>
    <servlet-class>com.servlet.RegServlet</servlet-class>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>ChatServlet</servlet-name>
    <servlet-class>com.servlet.ChatServlet</servlet-class>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.servlet.LoginServlet</servlet-class>
  </servlet>



  <servlet-mapping>
    <servlet-name>RegServlet</servlet-name>
    <url-pattern>/Reg.do</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>ChatServlet</servlet-name>
    <url-pattern>/Chat.do</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/Login.do</url-pattern>
  </servlet-mapping>
</web-app>


最后就是业务处理了： 
package com.method;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.LinkedList;
import java.util.Properties;

public class ChatService {
	private static ChatService cs;
	private Properties userList;
	private LinkedList<String> chatMsg;
	private ChatService()
	{}
	public static ChatService instance()
	{
		if(cs==null)
		{
			cs=new ChatService();
		}
		return cs;
	}
	public boolean validLogin(String user,String pass)throws IOException
	{
		if(loadUser().getProperty(user)==null)
		{
			return false;
		}
		if(loadUser().getProperty(user).equals(pass))
		{
			return true;
		}
		return false;
	}
	public boolean addUser(String name,String pass)throws Exception
	{
		if(userList==null)
		{
			userList=loadUser();
		}
		if(userList.containsKey(name))
		{
			throw new Exception("用户名已经存在，请重新选择用户名");
			
		}
		userList.setProperty(name,pass);
		saveUserList();
		return true;
	}
	public String getMsg()
	{
		if(chatMsg==null)
		{
			chatMsg=new LinkedList<String>();
			return "";
		}
		String result="";
		for(String tmp:chatMsg)
		{
			result+=tmp+"\n";
		}
		return result;
	}
	public void addMsg(String user,String msg)
	{
		if(chatMsg==null)
		{
		chatMsg=new LinkedList<String>();
		
		}
		if(chatMsg.size()>40)
		{
			chatMsg.removeFirst();
		}
		chatMsg.add(user+"说："+msg);
	}
	private Properties loadUser()throws IOException
	{
		if(userList==null)
		{
			File f=new File("userFile.properties");
			if(!f.exists())
				f.createNewFile();
			userList=new Properties();
			userList.load(new FileInputStream(f));
			
		}
		return userList;
	}
	private boolean saveUserList()throws IOException
	{
		if(userList==null)
		{
			return false;
		}
		userList.store(new FileOutputStream("userFile.properties"), "userList");
		return true;
	}
	
}



至此ajax聊天器的程序测试就这样完成了。
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