Ajax学习小例

1、js ajax

//Ajax实现检测用户名是否存在var xmlRequest;/***请求服务器*/function req(){//初始化xmlRequest对象try{xmlRequest = new XMLHttpRequest();// Firefox, Opera 8.0+, Safari}catch(e){try{xmlRequest = new ActiveXObject("Msxml2.XMLHTTP");//Internet Explorer}catch(e1){try{xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");}catch(e2){alert("强烈建议您更换浏览器！您的浏览器太OUT了!");}}}//设置xmlRequest回调函数xmlRequest.onreadystatechange=responseFn;//获取参数var userName = document.getElementById("userName").value;xmlRequest.open("GET", "checkRegName?userName="+userName+"&s="+new Date(), true);xmlRequest.send(null);}/***回调函数，等待处理服务器端回应*/function responseFn(){  if(xmlRequest.readyState==4){  if(xmlRequest.status==200){var responseText = xmlRequest.responseText;if(responseText==1){alert("换名吧！");}else{alert("贺喜贺喜！名字可用！");}  }  }}

2、jQuery Ajax实现

      需导入jq包，已经对中文乱码进行了处理

function req(){var userName = $("#userName").val();$.get("checkRegName",{userName:userName},function(data){alert(data);});}

在后台服务端的处理

response.setContentType("text/plain");PrintWriter out = response.getWriter();if(userName!=null&&userName.equals("admin")){out.print(1);}else{out.print(0);}out.flush();out.close();