点击页面先登录，登录后继续之前页面

Bertha 。 2022-08-08 11:47 216阅读 0赞

登录诸如当当网之类的购物网站，未登录前可以先将产品放入购物车，当点击结账的时候会先跳出登录页面，登录后，继续跳至结账页面。一直想写一个类似的demo，终于昨天写了一个，记录下来。

先看代码吧，看完再讲代码。

# 代码块    #

## 后台 ##

包含两个servlet，一个domain对象。

![SouthEast][]

CheckLogin.java

package com.login;
    
    import java.io.IOException;
    
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    /**
     * Servlet implementation class CheckLogin
     */
    @WebServlet("/res/viaLogin")
    public class CheckLogin extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public CheckLogin() {
            super();
        }
    
    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		
    		HttpSession session = request.getSession();
    		
    		User user = (User)session.getAttribute("user");
    		
    		String url = request.getParameter("url");
    		if (!"".equals(url)) {
    			session.setAttribute("url", url);
    		}
    		
    		if (null != user){
    			request.getRequestDispatcher("myOrder.jsp").forward(request, response);
    		} else {
    			request.getRequestDispatcher("login.jsp").forward(request, response);
    		}
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    }

LoginServlet.java

package com.login;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    /**
     * Servlet implementation class LoginServlet
     */
    @WebServlet("/res/login")
    public class LoginServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
        /**
         * @see HttpServlet#HttpServlet()
         */
        public LoginServlet() {
            super();
        }
    
    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		HttpSession session = request.getSession();
    		
    		User user = new User();
    		session.setAttribute("user", user);
    		
    		String url = (String) session.getAttribute("url");
    		if (null == url || "".equals(url)) {
    			request.getRequestDispatcher("main.jsp").forward(request, response); 
    		} else {
    			request.getRequestDispatcher(url).forward(request, response);
    		}
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    }

User.java

package com.login;
    
    public class User {
    
    }

## 前台页面 ##

![SouthEast 1][]

<%@ 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>Register</title>
    </head>
    <body>
    <center>
    	<form action="login">
    		<table>
    			<caption>登陆</caption>
    			<tr>
    				<td>username</td><td><input name="username" /></td>
    			</tr>
    			<tr>
    				<td>password</td><td><input name="password" type="password"/></td>
    			</tr>
    			<tr>
    				<td colspan="2" align="center"><input type="submit" value="Submit" /></td>
    			</tr>
    		</table>
    	</form>
    </center>
    </body>
    </html>

main.jsp

<%@ 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>Main</title>
    </head>
    <body>
    
    <center> This is main jsp <br><br>
    	<a href="#" οnclick="myOrder(this)">我的订单</a><br><br>
    	<a href="login.jsp">登陆</a>
    </center>
    
    <script type="text/javascript">
    	function myOrder(obj) {
        	var url = "myOrder.jsp";
            window.location.href = "viaLogin?url=" + url;
    	}
    </script>
    </body>
    </html>

myOrder.jsp

# 页面效果 #

## 主页面 ##

![Center][]

## 登录页面 ##

![Center 1][]

## 我的订单页面 ##

![Center 2][]

# 代码讲解 #

首页面包含内容

<center> This is main jsp <br><br>
    	<a href="#" οnclick="myOrder(this)">我的订单</a><br><br>
    	<a href="login.jsp">登陆</a>
    </center>
    
    <script type="text/javascript">
    	function myOrder(obj) {
        	var url = "myOrder.jsp";
            window.location.href = "viaLogin?url=" + url;
    	}
    </script>

其中点击我的订单时，请求登录验证，同时将我的订单页面的URL传递至后台。

登录验证servlet CheckLogin.java

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		
    		HttpSession session = request.getSession();
    		
    		User user = (User)session.getAttribute("user");
    		
    		String url = request.getParameter("url");
    		if (!"".equals(url)) {
    			session.setAttribute("url", url);
    		}
    		
    		if (null != user){
    			request.getRequestDispatcher("myOrder.jsp").forward(request, response);
    		} else {
    			request.getRequestDispatcher("login.jsp").forward(request, response);
    		}
    	}

先获取session，然后在session中获取该user对象。

同时，将URL后面的参数项url，即本应该跳转到的页面保存在session中。

若user对象不为空，则直接跳转至我的订单myOrder.jsp页面；如果user为空，则跳转至登录页面login.jsp页面。

登录servlet LoginServlet.java

/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		HttpSession session = request.getSession();
    		
    		User user = new User();
    		session.setAttribute("user", user);
    		
    		String url = (String) session.getAttribute("url");
    		if (null == url || "".equals(url)) {
    			request.getRequestDispatcher("main.jsp").forward(request, response); 
    		} else {
    			request.getRequestDispatcher(url).forward(request, response);
    		}
    	}

登录处理，new一个user出来，这里只是做示例，没有给user定义属性信息等，将user保存在session中，同时从session中获取到之前存放的url。

判断 url是否为null 或 空字符串：

如果是null或空字符串，则说明上一步的操作就是登录操作，这时候跳转至主页面main.jsp；

如果url不为null，则说明上一步应该是在访问某个页面，但是因为没有登录，被拦截到了登录页面，此时登录后，就应该继续之前的请求。

以上例子疏于整理，校验，如有不详尽之处，烦请提出，后面必改正，谢谢。

[SouthEast]: /images/20220805/420be424033541d4b6d93adc6b3ee718.png
[SouthEast 1]: /images/20220805/156dab1896e54925a2e477c28143b4b7.png
[Center]: /images/20220805/a069ccf54d4c4c35a4b776d47a6618c9.png
[Center 1]: /images/20220805/b65a988f123a4331917e7914f1239f9f.png
[Center 2]: /images/20220805/637c320247d94a2d83e8d7fe41928e5a.png