ajax的简洁封装
我相信大家都用过jquery的ajax，觉得很简练吧，不过我今天也对ajax进行了封装，跟jquery的ajax非常类似。
            
对ajax的封装如下：

var $= { 
		createXmlHttp : function () { 
						var xmlHttp = null; 
						try { 
							xmlHttp = new XMLHttpRequest(); 
						} catch (e) { 
							  try { 
								xmlHttp = new ActiveXObject('Msxml2.XMLHTTP'); 
							  }catch (ee) { 
									xmlHttp = new ActiveXObject('Microsoft.XMLHTTP'); 
							  } 
						} 
						return xmlHttp;
					 }, 
		ajax: function(ajaxInfo) { 
					  var xmlObj = $.createXmlHttp(); 
					  if (!xmlObj){ 
						  alert("很抱歉，你的浏览器暂时不支持Ajax。"); 
						  return; 
					  } 
					  var method = ajaxInfo.method.toUpperCase(); 
					  var method=ajaxInfo.method;
					  var data = null; 
					  xmlObj.open(method,ajaxInfo.url, true); 
					  if(method == "POST"){ 
						data = ajaxInfo.data;  
						xmlObj.setRequestHeader("CONTENT-TYPE", "application/x-www-form-urlencoded"); 
					  } 
					  xmlObj.send(data); 
					  xmlObj.onreadystatechange = function () { 
						  if(xmlObj.readyState == 4) { 
								 if(xmlObj.status == 200) { 
									   var type = ajaxInfo.type.toUpperCase(); 
									   if(type == "TEXT") { 
										   ajaxInfo.success(xmlObj.responseText); 
									   }else if(type == "XML") { 
										   ajaxInfo.success(xmlObj.responseXML); 
									   }else{  
										   alert("无法识别的返回方式"); 
								       } 
								      xmlObj = null; 
								} 
				          } 
			         }; 
					
		} 
	}

使用ajax的Post请求：

$.ajax({
		       method:"POST",
		       url:"servlet/AjaxServlet?time="+new Date().getTime(),
		       data:"username=abc&password=123",
		       type:"TEXT",
		       success:function (data) { 
					var jason = data ; 
					alert(jason);
		       }
   			
        });

  使用ajax的Get请求：

$.ajax({
		       method:"GET",
		       url:"servlet/AjaxServlet?username=abc&password=123&time="+new Date().getTime(),
		       data:null,
		       type:"TEXT",
               success:function (data) { 
 	   			  var jason = data ; 
   			      alert(jason);
               }
      	   			
           });

  
为了简单演示ajax的请求，在这里只是在AjaxServlet中作一个简单的验证。
AjaxServlet的代码：

package com.lrh.servlet;
	import java.io.IOException;
	import java.io.PrintWriter;
	import javax.servlet.ServletException;
	import javax.servlet.http.HttpServlet;
	import javax.servlet.http.HttpServletRequest;
	import javax.servlet.http.HttpServletResponse;
	
	public class AjaxServlet extends HttpServlet {
	
		@Override
		protected void doGet(HttpServletRequest request, HttpServletResponse response)
				throws ServletException, IOException {
			doPost(request,response);
		
		}
	
		@Override
		protected void doPost(HttpServletRequest request, HttpServletResponse response)
				throws ServletException, IOException {
			  String username=request.getParameter("username");
			  String password=request.getParameter("password");
			  PrintWriter out=response.getWriter();
			  if(username.equals("abc")&&password=="123"){
				  System.out.println("该用户已经存在");
				  out.print("该用户已被注册！");
			  }
			  out.flush();
			  	
		}
	   
	} 

AjaxServlet在web.xml中的配置：

 <servlet>
	    <servlet-name>AjaxServlet</servlet-name>
	    <servlet-class>com.lrh.servlet.AjaxServlet</servlet-class>
	  </servlet>
	  <servlet-mapping>
	    <servlet-name>AjaxServlet</servlet-name>
	    <url-pattern>/servlet/AjaxServlet</url-pattern>
	  </servlet-mapping>