拦截过滤器模式

2024 年 8 月 29 日 | 4 分钟阅读

拦截过滤器模式表明“如果你想在请求处理之前和之后拦截和操作请求和响应”。

用途

当你想要集中化、跨请求的公共处理时，例如记录关于每个请求的信息、压缩传出的响应或检查每个请求的数据编码方案。
当你想要预处理和后处理与核心请求处理服务松散耦合的组件时，这有利于添加和移除。

好处

它提供具有松散耦合处理程序的中央控制。
它提高了可重用性。

拦截过滤器模式的 UML 图

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>

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 {
		
		// get request parameters for username and passwd
        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");
            
            //setting session to expire in 1 hour
            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);
        }
	}
}//End of the LoginServlet class.

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>
<%
//allow access only if session exists
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;
            }
        }
        }
        //invalidate the session if exists
        HttpSession session = request.getSession(false);
        System.out.println("User="+session.getAttribute("user"));
        if(session != null){
            session.invalidate();
        }
        response.sendRedirect("Login.html");
    }

}//End of the LogoutServlet class

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{
            // pass the request along the filter chain
            chain.doFilter(request, response);
        }
    }
    public void destroy() {
        //close any resources here
    }
}//End of the AuthenticationFilter class

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()+"}");
            }
        }
        // pass the request along the filter chain
        chain.doFilter(request, response);
    }
 
    public void destroy() {
        //we can close resources here
    }
}// End of the RequestLoggingFilter class

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