ajax表单验证后台用户名是否存在

package ajaxservlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import db.DBconnection;

public class AjaxServlet extends HttpServlet {

	//private static final long serialVersionUID = 1L;

	public void destroy() {
		try {
			DBconnection.connectionClose();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public 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 name=request.getParameter("username");
		String pass=request.getParameter("userpass");
		String pass2=request.getParameter("userpass2");
		
		String a=request.getParameter("a");
		String b=request.getParameter("b");
		
		System.out.println(name+" "+pass);
		System.out.println("a "+a);
		System.out.println("b "+b);
		request.setAttribute("name",name);
		System.out.println(name);
		
		try {
			if(checkName(name))
			{
				System.out.println(checkName(name));
				System.out.println("checkname="+name);
				out.write("用户名已经存在，请重新输入!");
				System.out.println("xxxxxxxxxxxxxxxxx");
				request.setAttribute("error.message","用户名已经存在");
			}
			else
			{
				out.write("此用户名合法");
			}
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			out.close();
			e.printStackTrace();
		}
	}

	public boolean checkName(String name) throws SQLException   //检查用户名是否存在
	{
		boolean flag=false;
		Connection conn=DBconnection.getConnection();
		System.out.println("conn="+conn);
		/*String sql="select * from a_user where username='"+name+"'";
		System.out.println("name="+name);
		Statement state=conn.createStatement();
		ResultSet rs=state.executeQuery(sql);*/
		String sql="select * from a_user where username=?";
		PreparedStatement pstate=conn.prepareStatement(sql);
		pstate.setString(1,name);
		ResultSet rs=pstate.executeQuery();
		//System.out.println(rs.getInt(0));
		//System.out.println(rs.getString("username"));
		while(rs.next())
		{
			System.out.println("rs.getString(username)="+rs.getString("username"));
			flag=true;
		}
		return flag;
	}
	
	public void doPost(HttpServletRequest request,IOException {

		
		//response.setContentType("text/html");
		this.doGet(request,response);
	}

	
	public void init() throws ServletException {
		
	}

}

//以下是ajax部分
var xmlhttp;

function ajaxfun()
{
	
	if (window.XMLHttpRequest)
	  {// code for IE7+,Safari
	  xmlhttp=new XMLHttpRequest();
	  }
	else
	  {// code for IE6,IE5
	  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	  }
	return xmlhttp;
}

window.onload=function()
{
	
	document.getElementById("username1").onblur=function()
	{
		var name=document.getElementsByName("username")[0].value;
		xmlhttp=ajaxfun();
		xmlhttp.onreadystatechange=check;
		//xmlhttp.open("get","http://localhost:8080/ajaxtest/AjaxServlet?username="+name+"&time="+new Date().toTimeString(),true);
		//以下是get方法传值
		/*xmlhttp.open("get","./AjaxServlet?username="+name+"&time="+new Date().toTimeString(),true);
		xmlhttp.send(null);*/
		
		/*
		 * 如果需要像 HTML 表单那样使用 POST 传递数据，请使用 setRequestHeader() 来添加 HTTP 头。
		 * 然后在 send() 方法中规定您希望发送的数据：
		 */
		xmlhttp.open("post",true);
		xmlhttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded")
		xmlhttp.send("a=100&b=222");
		
	}
	
}
function check()
{
	alert(xmlhttp.status);
	if(xmlhttp.readyState==4 && xmlhttp.status==200)
	{
		alert(xmlhttp.status);
		document.getElementById("span").innerHTML=xmlhttp.responseText;
	}
}

（编辑：李大同）

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