AJAX异步提交

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ajax实时验证用户名是否存在

1、jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>









用户名：


密码：

 2、web.xml

  
  
    AjaxServlet
    com.servlet.AjaxServlet
  
  
    AjaxServlet
    /ajax
  

 3、servlet

package com.servlet;

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 AjaxServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doPost(request, response);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("UTF-8");
		response.setContentType("text/html;charset=UTF-8");
		PrintWriter out = response.getWriter();
		
		String userName = request.getParameter("userName");
		
		if(userName.equals("admin")){
			out.print("用户名已经存在");
		}
		else if (userName.length() == 0) {
			out.print("用户不能为空");
		}
		else if (userName.indexOf(" ") > 0) {
			out.print("用户不能含有空格");
		}
		else if (userName.length() > 10 || userName.length() < 4) {
			out.print("用户长度在4-10之间");
		}
		else {
			out.print("用户名可用");
		}
		out.flush();
		out.close();
	}
}