Ajax检测用户名是否已经注册

程序功能

当用户名输入完成（即用户名输入框失去焦点），利用Ajax检测用户名是否已经注册！

实现过程

利用Ajax向CheckUserServlet发送请求，判断该用户名是否可用。这里只是为了演示Ajax的用法，就不访问数据库了，直接设置一些用户名就好了，模拟一下即可。

关于中文编码的处理

坑爹，在javascript中传递中文参数，需要先编码，然后解码。详细见JavaScript利用URL向后台传入中文参数乱码问题解决之道。

运行截图

运行结果

代码实例

JSP页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>检查用户名是否唯一</title>
</head>
<script type="text/javascript">
    function checkUser(username) {
        if (username.value == "") {
            alert("请输入用户名!");
            username.focus();
            return;
        } else {
            createRequest('CheckUserServlet?user='+encodeURI(encodeURI(username.value)));
        }
    }
    function createRequest(url) {
        http_request = false;
        if (window.XMLHttpRequest) {
            http_request = new XMLHttpRequest();
        } else if (window.ActiveXObject) {
            try {
                http_request = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    http_request = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (e) {

                }
            }
        }

        if (!http_request) {
            alert("不能创建XMLHttpRequest对象实例!");
            return false;
        }
        //alert("创建成功!");
        http_request.onreadystatechange = getResult;
        http_request.open('GET', url, true);
        http_request.send(null);
    }
    function getResult() {
        if (http_request.readyState == 4) { //请求已经完成
            if (http_request.status == 200) { //请求成功
                document.getElementById("msg").innerHTML = http_request.responseText;
            } else {
                alert("你请求的页面有错误!");
            }
        }
    }
</script>
<body>
<form method="post" name="registForm">
    用户名：<input type="text" name="username" id="username" onblur="checkUser(registForm.username);">
    <div id="msg"></div><br>
    密   码：<input type="password" >
</form>
</body>
</html>

检查是非已经注册的工具类

package cn.edu.pzhu.servlet.util;

public class UserUtils {
    private static String[] userList = {"张三", "李四", "Tom", "Jerry"};

    public static boolean checkUser(String username) {
        boolean ok = true;
        for (int i = 0; i < userList.length; i++) {
            if (username.equals(userList[i])) {
                ok = false;
                break;
            }
        }
        return ok;
    }
}

servlet处理

package cn.edu.pzhu.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.jasper.tagplugins.jstl.core.Out;

import cn.edu.pzhu.servlet.util.UserUtils;

/**
 * Servlet implementation class CheckUserServlet
 */
@WebServlet("/CheckUserServlet")
public class CheckUserServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public CheckUserServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("user");
        //解码
        username = URLDecoder.decode(username, "UTF-8");
        System.out.println(username);
        PrintWriter out = response.getWriter();
        if (UserUtils.checkUser(username)) {
            out.print("该用户名可用!");
        } else {
            out.print("该用户名不可用!");
        }
        //request.getRequestDispatcher("index.jsp").forward(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

如有不当之处欢迎指出！