我的ajax请求错哪里了，为什么总是出错
HTML代码
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
</head>
<body>
<script type="text/javascript">
var xhr=new XMLHttpRequest()
window.onload=function(){
document.getElementById("in").onclick=function(){
xhr.open("POST","/text1_war_exploded/ajax",true)
var name=document.getElementById("name").value;
var pass=document.getElementById("pass").value;
xhr.setRequestHeader("content-Type","application/x-www-form-urlencoded")
xhr.send("name="+name+"&pass="+pass)
xhr.onreadystatechange=function (){
if(xhr.onreadystatechange==4){
document.getElementById("span").innerHTML=xhr.responseText}
if(xhr.onreadystatechange==2){
document.write("请求已经收到")}
if(xhr.onreadystatechange==1){
document.write("服务器已经建立连接")}
}
}
}
</script>
用户名<input type="text" name="name" id="name" /><br>
密码<input type="password" name="pass" id="pass" /><br>
<input type="button" name="" id="in" value="提交" />
<span id="span">rfe4</span>
</body>
</html>
Java代码
```java
@WebServlet(value = "/ajax")
public class ajax extends HttpServlet {
public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
PrintWriter p=response.getWriter();
String name=request.getParameter("name");
String pass=request.getParameter("pass");
if(name.equals("sb")){
p.write("用户名不存在或者密码错误");
}
else {
p.write("用户名不存在或者密码错误");
}
}
}
