使用JavaScript与Servlet实现客户端与服务器端验证

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下面写一个注册页面

Js代码  
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>  
<html>  
    <head>  
        <script type="text/javascript">  
            function validate(){  
                //通过id来取值   
                var username = document.getElementById("username1");  
                var password = document.getElementById("password1");  
                var repassword = document.getElementById("repassword1");  
                  
                /*通过名称来取值，不过返回的是数组，只取数组中的第一个值 
                  var username = document.getElementsByName("username")[0]; 
                  var password = document.getElementsByName("password")[0]; 
                  var repassword = document.getElementsByName("repassword")[0];*/  
                  
                /*或通过getElementsByTagName来取值，同样，它返回的也是一个数组 
                var inputs = document.getElementsByTagName("input"); 
                for(var i =0;i<inputs.length;i++){ 
                    alert(inputs[i].value); 
                }*/  
                //用户名不能为空  
                if(username.value == ""){  
                    alert("username can't be null!");  
                    return false;  
                }  
                //密码长度不能少于6  
                if(password.value.length < 6 || repassword.value.length < 6 ){  
                    alert("password'length can't less than 6");  
                    return false;   
                }  
                //密码不相同  
                if(password.value != repassword.value){  
                    alert("password not same!");  
                    return false;  
                }  
                  
            }  
        </script>  
    </head>  
  <body>  
    <!-- <form action="ValidateServlet" onsubmit="return validate()">  -->  
    <form action="ValidateServlet">  
        username:<input type="text" name="username" id="username1"><br>  
        password:<input type="password" name="password" id="password1"><br>  
        repassword:<input type="password" name="repassword" id="repassword1"><br>  
        <input type="submit" value="submit">  
    </form>  
  </body>  
</html>  

ValidateServlet.java 在后台进行验证

Java代码  
package com.kingdee.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;  
  
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(username == null || "".equals(username)){  
            list.add("username can't be null");  
        }  
        if(password.length() <6 || repassword.length() <6){  
            list.add("password can't less than 6");  
        }  
        if(!password.equals(repassword)){  
            list.add("password not same");  
        }  
        if(list.isEmpty()){  
            request.setAttribute("username", username);  
            request.setAttribute("password", password);  
            request.setAttribute("repassword", repassword);  
            request.getRequestDispatcher("success.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 {  
        super.doPost(request, response);  
    }  
  
}  

success.jsp

Html代码  
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>  
<html>  
  <body>  
    <%  
        String username = (String)request.getAttribute("username");  
        String password = (String)request.getAttribute("password");  
        String repassword = (String)request.getAttribute("repassword");  
     %>  
     username:<%=username %><br>  
     password:<%=password %><br>  
     repassword:<%=repassword %>  
  </body>  
</html>  

error.jsp

Html代码  
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>  
  
<html>  
  <body>  
     <%  
        List<String> list = (List<String>)request.getAttribute("error");  
     %>  
     <h1>Register Failed!</h1>  
     <%  
        for(String str:list){  
            out.println(str+"<br>");  
        }  
      %>  
  </body>  
</html>  

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