regservlet.java
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String name=request.getParameter("uname");
PrintWriter out=response.getWriter();
if("admin".equals(name)) {
out.write("no");
}
else out.write("yes");
}
reg.jsp
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script type="text/javascript" src="js/jquery-3.5.1.min.js">
</script>
<script type="text/javascript">
$(function(){
$("#uname").blur(function(){
$.get("ajax?name="+$(this).val(),function(data){
$("#span").html(data);
});
});
});
</script>
</head>
<body>
<form action="ajax" method="get">
用户名:<input type="text" name="uname" id="uname"/>
<br/>
<input type="submit"/>
</form>
</body>
</html>