AJAX用于判定用户是否注册的教程

var xmlHttp;

var flag;

function createXMLHttp(){

if(window.XMLHttpRequest){

xmlHttp=new XMLHttpRequest();

}else{

xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");

}

}

function checkUserid(userid){

createXMLHttp();

xmlHttp.open("POST","CheckServlet?userid="+userid);

xmlHttp.onreadystatechange=checkUseridCallback;

xmlHttp.send();

document.getElementById("msg").innerHTML="正在验证。。。";

}

function checkUseridCallback(){

if(xmlHttp.readyState==400){

if(xmlHttp.status==200){

var text=xmlHttp.responseText;

if(text=="true"){

flag=false;

document.getElementById("msg").innerHTML="用户ID重复，无法使用";

}else{

flag=true;

document.getElementById("msg").innerHTML="此用户ID可以注册";

}

}

}

}

function checkForm(){

return flag;

}

用户ID

姓名：

密码：

importjava.io.IOException;

importjava.io.PrintWriter;

importjava.sql.Connection;

importjava.sql.DriverManager;

importjava.sql.PreparedStatement;

importjava.sql.ResultSet;

importjava.sql.SQLException;

importjavax.servlet.ServletException;

importjavax.servlet.http.HttpServlet;

importjavax.servlet.http.HttpServletRequest;

importjavax.servlet.http.HttpServletResponse;

publicclassCheckServletextendsHttpServlet{

publicstaticfinalString DBDRIVER ="oracle.jdbc.OracleDriver";

publicstaticfinalString DBURL ="jdbc:oracle:thin:@59.173.240.149:1521:heer";

publicstaticfinalString DBUSER ="hnsyu_dev";

publicstaticfinalString DBPASS ="hnsyuok";

publicvoiddoGet(HttpServletRequest request,HttpServletResponse response)

throwsServletException,IOException{

this.doPost(request, response);

}

publicvoiddoPost(HttpServletRequest request,HttpServletResponse response)

throwsServletException,IOException{

request.setCharacterEncoding("gbk");

response.setContentType("text/html");

Connection connection =null;

PreparedStatement preparedStatement =null;

ResultSet resultSet =null;

PrintWriter out = response.getWriter();

String userid = request.getParameter("userid");

try{

Class.forName(DBDRIVER);

connection = DriverManager.getConnection(DBURL, DBUSER, DBPASS);

String sql ="select count(userid) from userdemo where userid=?";

preparedStatement = connection.prepareStatement(sql);

preparedStatement.setString(1,userid);

resultSet = preparedStatement.executeQuery();

if(resultSet.next()) {

if(resultSet.getInt(1)>0){

out.print("false");

System.out.println("true");

}else{

out.print("false");

}

}

out.close();

}catch(Exception e) {

e.printStackTrace();

}finally{

try{

connection.close();

}catch(Exception e) {

e.printStackTrace();

}

}

}

}

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_3_0.xsd">

  index.jsp

 CheckServlet

 CheckServlet

 CheckServlet

 /CheckServlet