Ajax异步更新网页（使用原生JavaScript）

一、页面代码

<!DOCTYPE html>
<html>
<head>
<title>MyHtml.html</title>

<meta name="keywords" content="keyword1,keyword2,keyword3">
<meta name="description" content="this is my page">
<meta name="content-type" content="text/html; charset=UTF-8">

<body>
    <table>
        <tr>
            <td>Login:</td>
            <td><input id="username" type="text" name="login"></td>
        </tr>
        <tr>
            <td>Password:</td>
            <td><input type="password" name="password" id="password"></td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit"></td>
        </tr>
    </table>
</body>
</html>

二、JavaScript代码

<script type="text/javascript">
    var xmlHttp;
    $(document).ready(function() {
        $("#username").keyup(function() {
            var value = $(this).val();

            xmlHttp = createXMLHttp();
            var url = "MyServlet1?username=" + value;
            xmlHttp.open("GET", url, true);
            xmlHttp.onreadystatechange = callback;
            xmlHttp.send(null);
        });
    });

    function createXMLHttp() {
        var xmlHttp;
        if (window.XMLHttpRequest) {
            xmlHttp = new XMLHttpRequest();
        } else {
            xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        return xmlHttp;
    }

    var callback = function() {

        if (xmlHttp.status == 200 && xmlHttp.readyState == 4) {
            var result = xmlHttp.responseText;
            if (result == "已使用")
                $("#username").css("border-color", "red");
            else
                $("#username").css("border-color", "green");
        } else {
            alert("出错");
        }
    }
</script>

三、servlet代码

package com.yh.myServlet;

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 MyServlet1 extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        String userName = request.getParameter("username");
        System.out.println(userName);
        if (userName.equals("yh")) {
            out.print("已使用");
        } else {
            out.print("可使用");
        }
    }
}

四、配置servlet

  <servlet>
      <servlet-name>MyServlet1</servlet-name>
      <servlet-class>com.yh.myServlet.MyServlet1</servlet-class>
  </servlet>
  
  <servlet-mapping>
      <servlet-name>MyServlet1</servlet-name>
      <url-pattern>/Pages/MyServlet1</url-pattern>
  </servlet-mapping>

注：这个Pages是根据html页面的路径设置的

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原文地址：https://www.cnblogs.com/YeHuan/p/10993862.html