利用Servlet和jsp实现客户端与服务器端的用户登录信息验证

首先编写登录页面mylogin.jsp
编写表单：
[java]
<form onsubmit="return valdate()">

username: <input type="text" name = "username" id="username"><br/>
password: <input type="password" name = "password" id="password"><br/>
repassword: <input type="password" name = "repassword" id="repassword"><br/>

<input type="submit" value="submit"/>
<input type="reset" value="reset"/>


</form>
第一种验证的方式：利用javascript在客户端实现验证
[java]
<script type="text/javascript">

function valdate(){
//var username = document.getElementById("username");
//var password = document.getElementById("password");
//var repassword = document.getElementById("repassword");

var username = document.getElementsByName("username")[0];
var password = document.getElementsByName("password")[0];
var repassword = document.getElementsByName("repassword")[0];

if(username.value.length == 0){

alert("username can not be blank");
return false;
}

if(password.value.length < 6 || password.value.length > 11){

   alert("length of password is invalid");
return false;

}
if(password.value != repassword.value> 11){

   alert("password is not the same with repassword");
return false;

}
return true;

}


</script>
如上面的代码所示，在表单中调用javascript的函数实现客户端验证。
第二种验证的方式：用Servlet实现验证
编写ValidateServlet.java类
[java]
package com.lcq.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

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

@SuppressWarnings("serial")
public class ValidateServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String repassword = request.getParameter("repassword");
        List<String> list = new ArrayList<String>();
        if(null == username || "".equals(username)){
            list.add("username can't be blank!");
        }
        if(password == null ||password.length() < 6 ||password.length() > 10){
            list.add("length of password should be between 6 and 10");
        }
        if(repassword == null ||repassword.length() < 6 || repassword.length() > 10){
            list.add("length of repassword should be between 6 and 10");
        }
        if(password != null && repassword != null && !password.equals(repassword)){
            list.add("password and repassword not the same!");
        }


        if(list.isEmpty()){
            request.setAttribute("username", username);
            request.setAttribute("password", password);
            request.getRequestDispatcher("sucess.jsp").forward(request, response);
        }else{
            request.setAttribute("error",list);
            request.getRequestDispatcher("error.jsp").forward(request, response);;
        }


    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
         doGet(request, response);

    }

}
在Servlet中处理完成后转到sucess.jsp或者error.jsp
以下是sucess.jsp
[java]
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>


    <title>My JSP 'sucess.jsp' starting page</title>

    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type=&qu

补充：软件开发 , Java ,