AJAX用于判定用户是否注册

在很多注册的页面上，我们可能会遇到以下情况，当我们注册用户名的时候可能会提示该用户名已注册，其实现是应用AJAX技术。

首先写一个登陆页面

<html>
<head>
<title></title>
<script type="text/javascript">
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;
}

</script>
</head>
<body>

<form action="tt.jsp" method="post" onsubmit="return checkForm()">
用户ID <input type="text" name="userid" onblur="checkUserid(this.value)"><span id="msg"></span><br>
姓名：<input type="text" name="name"><br>
密码：<input type="password" name="password"><br>
<input type="button" value="注册">
<input type="reset" value="重置">
</form>
</body>
</html>

随后写一个servlet的Java代码

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CheckServlet extends HttpServlet{
public static final String DBDRIVER = "oracle.jdbc.OracleDriver";
public static final String DBURL = "jdbc:oracle:thin:@59.173.240.149:1521:heer";
public static final String DBUSER = "hnsyu_dev";
public static final String DBPASS = "hnsyuok";

public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException{
this.doPost(request, response);
}

public void doPost(HttpServletRequest request,HttpServletResponse response)
throws ServletException,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();
}
}
}
}

其中还需要在web.xml中进行配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
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">
 <display-name></display-name>
 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
  <servlet>
 <servlet-name>CheckServlet</servlet-name>
 <servlet-class>CheckServlet</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>CheckServlet</servlet-name>
 <url-pattern>/CheckServlet</url-pattern>
 </servlet-mapping>
</web-app>

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