Design Patterns教程-拦截过滤器模式

拦截过滤器模式的定义是“如果你想在请求处理前后拦截和操作请求和响应”。

使用场景：

当你希望集中处理请求的通用处理，例如记录每个请求的信息、压缩响应或检查每个请求的数据编码方案。
当你希望对松散耦合的核心请求处理服务进行前处理和后处理时，这些服务不适合添加和移除。

优点：

它提供了中心控制和松散耦合的处理器。
它提高了代码的可重用性。

拦截过滤器模式的UML：

拦截过滤器模式的实现：

步骤 1

创建一个Login.html网页。

<!DOCTYPE html> 
<html> 
<head> 
<meta charset="US-ASCII"> 
<title>Login Page</title> 
</head> 
<body> 
    <form action="LoginServlet" method="post"> 
        Username: <input type="text" name="username"> 
        <br><br> 
        Password: <input type="password" name="password"> 
        <br><br> 
        <input type="submit" value="Login"> 
    </form> 
</body> 
</html>

步骤 2

创建一个LoginServlet类。

package sessions;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
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("/LoginServlet")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private final String user = "admin";
    private final String password = "admin@1234";

    public LoginServlet() {
        super();
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取请求参数中的用户名和密码
        String username = request.getParameter("username");
        String passwd = request.getParameter("password");
        
        if(user.equals(username) && password.equals(passwd)){
            HttpSession session = request.getSession();
            session.setAttribute("user", "ashwani");
            
            // 设置会话过期时间为1小时
            session.setMaxInactiveInterval(60*60);
            
            Cookie userName = new Cookie("user", user);
            userName.setMaxAge(60*60);
            response.addCookie(userName);
            response.sendRedirect("LoginSuccess.jsp");
        } else {
            RequestDispatcher rd = getServletContext().getRequestDispatcher("/Login.html");
            PrintWriter out= response.getWriter();
            out.println("<font color=red>Either user name or password is wrong.</font>");
            rd.include(request, response);
        }
    }
}

步骤 3

创建一个LoginSuccess.jsp页面。

<%@ page language="java" contentType="text/html; charset=US-ASCII" 
    pageEncoding="US-ASCII"%>
<!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=US-ASCII">
<title>Login Success Page</title>
</head>
<body>
<%
    // 仅在会话存在时允许访问
    String user = (String) session.getAttribute("user");
    String userName = null;
    String sessionID = null;
    Cookie[] cookies = request.getCookies();
    if(cookies != null){
        for(Cookie cookie : cookies){
            if(cookie.getName().equals("user")) userName = cookie.getValue();
            if(cookie.getName().equals("JSESSIONID")) sessionID = cookie.getValue();
        }
    }
%>
<h3>Hi <%=userName %>, Login successful. Your Session ID=<%=sessionID %></h3>
<br>
User=<%=user %>
<br>
<a href="CheckoutPage.jsp">Checkout Page</a><br>
<form action="LogoutServlet" method="post">
<input type="submit" value="Logout" >
</form>
</body>
</html>

步骤 4

创建一个AdminPage.jsp页面。

<%@ page language="java" contentType="text/html; charset=US-ASCII" 
    pageEncoding="US-ASCII"%>
<!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=US-ASCII">
<title>Login Success Page</title>
</head>
<body>
<%
    String userName = null;
    String sessionID = null;
    Cookie[] cookies = request.getCookies();
    if(cookies != null){
        for(Cookie cookie : cookies){
            if(cookie.getName().equals("user")) userName = cookie.getValue();
        }
    }
%>
<h3>Hi <%=userName %>, These services are only for you to take action.</h3>
<br>
<form action="LogoutServlet" method="post">
<input type="submit" value="Logout" >
</form>
</body>
</html>

步骤 5

创建一个LogoutServlet类。

package sessions;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class LogoutServlet
 */
@WebServlet("/LogoutServlet")
public class LogoutServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        Cookie[] cookies = request.getCookies();
        if(cookies != null){
            for(Cookie cookie : cookies){
                if(cookie.getName().equals("JSESSIONID")){
                    System.out.println("JSESSIONID="+cookie.getValue());
                    break;
                }
            }
        }
        // 如果会话存在则使其失效
        HttpSession session = request.getSession(false);
        System.out.println("User="+session.getAttribute("user"));
        if(session != null){
            session.invalidate();
        }
        response.sendRedirect("Login.html");
    }
}

步骤 6

创建一个AuthenticationFilter类。

package filters;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet Filter implementation class AuthenticationFilter
 */
@WebFilter("/AuthenticationFilter")
public class AuthenticationFilter implements Filter {

    private ServletContext context;
    
    public void init(FilterConfig fConfig) throws ServletException {
        this.context = fConfig.getServletContext();
        this.context.log("AuthenticationFilter initialized");
    }
    
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse res = (HttpServletResponse) response;
        
        String uri = req.getRequestURI();
        this.context.log("Requested Resource::"+uri);
        
        HttpSession session = req.getSession(false);
        
        if(session == null && !(uri.endsWith("html") || uri.endsWith("LoginServlet"))){
            this.context.log("Unauthorized access request");
            res.sendRedirect("Login.html");
        } else {
            // 将请求传递给过滤器链
            chain.doFilter(request, response);
        }
    }
    
    public void destroy() {
        // 关闭任何资源
    }
}

步骤 7

创建一个RequestLoggingFilter类。

package filters;

import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;

@WebFilter("/RequestLoggingFilter")
public class RequestLoggingFilter implements Filter {
    private ServletContext context;
    
    public void init(FilterConfig fConfig) throws ServletException {
        this.context = fConfig.getServletContext();
        this.context.log("RequestLoggingFilter initialized");
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) request;
        Enumeration<String> params = req.getParameterNames();
        while(params.hasMoreElements()){
            String name = params.nextElement();
            String value = request.getParameter(name);
            this.context.log(req.getRemoteAddr() + "::Request Params::{"+name+"="+value+"}");
        }
        
        Cookie[] cookies = req.getCookies();
        if(cookies != null){
            for(Cookie cookie : cookies){
                this.context.log(req.getRemoteAddr() + "::Cookie::{"+cookie.getName()+","+cookie.getValue()+"}");
            }
        }
        // 将请求传递给过滤器链
        chain.doFilter(request, response);
    }
    
    public void destroy() {
        // 可以在这里关闭资源
    }
}

步骤 8

创建一个web.xml文件。

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
    <display-name>ServletFilterExample</display-name>
    <welcome-file-list>
        <welcome-file>Login.html</welcome-file>
    </welcome-file-list>
    <filter>
        <filter-name>RequestLoggingFilter</filter-name>
        <filter-class>filters.RequestLoggingFilter</filter-class>
    </filter>
    <filter>
        <filter-name>AuthenticationFilter</filter-name>
        <filter-class>filters.AuthenticationFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>RequestLoggingFilter</filter-name>
        <url-pattern>/*</url-pattern>
        <dispatcher>REQUEST</dispatcher>
    </filter-mapping>
    <filter-mapping>
        <filter-name>AuthenticationFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

输出：

通过上述实现，我们可以看到拦截过滤器模式如何拦截和操作请求和响应，并提供了中心控制和松散耦合的处理器。

Design Patterns教程-拦截过滤器模式

使用场景：

优点：

拦截过滤器模式的UML：

拦截过滤器模式的实现：

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