17-Ajax使用get/post方式，判断用户名是否重复

<%@ 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>Insert title here</title>
<script type="text/javascript">
	var xmlHttpRequest=null;
	//创建Ajax引擎
	function getXmlHttpRequest() {
			if (window.ActiveXObject) {
				//ie
				xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP");
			} else {
				//firefox
				xmlHttpRequest = new XMLHttpRequest();
			}
	}
	//检查用户名是否重复
	function checkUserName() {
		//创建ajax引擎
		getXmlHttpRequest();
		//如果ajax引擎创建成功
		if (xmlHttpRequest) {
			//第一个参数表示请求的方式get/post
			//第二个参数指定url
			//第三个参数true表示使用异步机制
			//如果使用get方法请求，第一次进行请求，第二次从缓存里面取
// 			var url = "/Ajax/CheckUserName?username="+$("username").value;
			var url = "/Ajax/CheckUserName";
			//post提交数据
			var data="username="+$("username").value;
			//xmlHttpRequest.open("get",url,true);
			xmlHttpRequest.open("post",true);
			xmlHttpRequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
			//回调函数
			xmlHttpRequest.onreadystatechange =chuli;
			//发送请求,如果是get，写null， 可以传参数
			//xmlHttpRequest.send(null);
			xmlHttpRequest.send(data);
		}
	}

	//回调函数
	function chuli() {
		if (xmlHttpRequest.readyState == 4) {
			$("res").innerHTML=xmlHttpRequest.responseText;
		}
	}

	//$方法
	function $(id) {
		return document.getElementById(id);
	}
</script>
</head>
<body>
	用户名:(输入aaa重复)
	<input type="text" id="username" onkeyup="checkUserName();" />
	<span id="res" style="color: red;"></span>
</body>
</html>

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;

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

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

	protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
		response.setContentType("text/html; charset=utf-8");
		response.setHeader("Cache-Control","no-cache");
		PrintWriter out=response.getWriter();
		String username=request.getParameter("username");
		if(username.equals("aaa")){
			out.print("GET:用户名重复");
		}else{
			out.print("GET:用户名可以使用");
		}
		out.close();
	}
	@Override
	protected void doPost(HttpServletRequest req,HttpServletResponse resp)
			throws ServletException,IOException {
		resp.setContentType("text/html; charset=utf-8");
		resp.setHeader("Cache-Control","no-cache");
		PrintWriter out=resp.getWriter();
		String username=req.getParameter("username");
		if(username.equals("aaa")){
			out.print("POST:用户名重复");
		}else{
			out.print("POST:用户名可以使用");
		}
		out.close();
	}
}

原文链接：https://www.f2er.com/ajax/162491.html

17-Ajax使用get/post方式，判断用户名是否重复

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