关于JS发送Ajax到servlet的问题

上代码：
JSP页面：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ path + "/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>"> <title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">

<script type="text/javascript">
function test() {
var xhr = null;
if (window.XMLHttpRequest) {
//非IE浏览器
alert("非IE浏览器");
xhr = new XMLHttpRequest();
} else {
//IE
alert("IE浏览器");
xhr = new ActiveXObject("Microsoft.XMLhttp");
}
xhr.open('post', 'checkName.do', true);
xhr.setRequestHeader('content-type',
'application/x-www-form-urlencoded');
xhr.onreadystatechange = function() {
if (xhr.readyState == 4) {
var txt = xhr.responseText;
document.getElementById('msg').innerHTML = txt;
}
};
var v = document.getElementById('username').value;
alert(v);
x.send('username=' +v);
}
</script>
</head> <body>
<form action="" method="post">
<table>
<tr>
<td>
用户名:
</td>
<td>
<input type="text" name="username" id="username" />
</td>
<td>
<input type="button" value="检测用户名是否可用" onclick="test();">
<span id="msg" style="font-size: 12px; color: red"></span>
</td>
</tr>
</table>
</form>
</body>
</html>
web.xml<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 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_2_5.xsd">
<display-name></display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list> <servlet>
<servlet-name>servlet</servlet-name>
<servlet-class>cn.com.leamon.Action</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>servlet</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
</web-app>
servlet:
package cn.com.leamon;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 Action extends HttpServlet{ /**
*
*/
private static final long serialVersionUID = 4712705254757428362L;

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();

String username = request.getParameter("username");
System.out.println(username);
if(username.equals("张三")){
out.println("用户名已被注册!");
}else{
out.println("用户名可用");
}
}
}
问题在于xhr.open('post', 'checkName.do', true);发了请求之后服务器端没有反应，求原因。

解决方案 »

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在servlet的web.xml配置文件中将servlet-mapping的url-pattern下的*.do前加一个/这才是完整的
js 代码
<script type="text/javascript">
var xmlhttp;
function loadXMLDoc()
{
xmlhttp=null;
if (window.XMLHttpRequest)
  {// code for all new browsers
  xmlhttp=new XMLHttpRequest();
  }
else if (window.ActiveXObject)
  {// code for IE5 and IE6
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
if (xmlhttp!=null)
  {
// document.getElementById('username').value;
  xmlhttp.onreadystatechange=state_Change;
  xmlhttp.open("post","<%=path%>/aa.do?username="+document.getElementById('username').value,true);
  xmlhttp.send(null);
  }
else
  {
  alert("Your browser does not support XMLHTTP.");
  }
}function state_Change()
{
if (xmlhttp.readyState==4)
  {// 4 = "loaded"
  if (xmlhttp.status==200)
    {
    alert(xmlhttp.responseText);
    document.getElementById('A3').innerHTML=xmlhttp.responseText;    }
  else
    {
    alert("Problem retrieving XML data");
    }
  }
}

</script>web.xml代码
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 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_2_5.xsd">
<servlet>
<servlet-name>servlet</servlet-name>
<servlet-class>com.tes.servlerlteAjax.Action</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>servlet</servlet-name>
<url-pattern>/aa.do</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>servlet 没改你的希望对你有用，经过测试可以通过