Java WEB之过滤器

过滤器是什么玩意？

所谓过滤器，其实就是一个服务端组件，用来截取用户端的请求与响应信息。

过滤器的应用场景：
1.对用户请求进行统一认证，保证不会出现用户账户安全性问题

2.编码转换，可在服务端的过滤器中设置统一的编码格式，避免出现乱码

3.对用户发送的数据进行过滤替换

4.转换图像格式

5.对响应的内容进行压缩

其中，第1,2场景经常涉及。

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'login.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="text/css" href="styles.css">--></head><body><form action="<%=path %>/servlet/LoginServlet" method="post" >用户名:<input type="text" name="username" />密码:<input type="password" name="password" /><input type="submit" value="登录" /></form></body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="utf-8" contentType="text/html; charset=utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.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="text/css" href="styles.css">--></head><body></body>
</html>

success.jsp

<%@ page language="java" import="java.util.*" contentType="text/html; charset=utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'login.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="text/css" href="styles.css">--></head><body>登录失败，请检查用户名或密码！</body>
</html>

failure.jsp

package com.cityhuntshou.filter;import java.io.IOException;import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;public class LoginFilter implements Filter {private FilterConfig config;public void destroy() {}public void doFilter(ServletRequest arg0, ServletResponse arg1,FilterChain arg2) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest) arg0;HttpServletResponse response = (HttpServletResponse) arg1;HttpSession session = request.getSession();//过滤器实际应用场景之二-----编码转换
        String charset = config.getInitParameter("charset");if(charset == null){charset = "UTF-8";}request.setCharacterEncoding(charset);String noLoginPaths = config.getInitParameter("noLoginPaths");if(noLoginPaths != null){String[] strArray = noLoginPaths.split(";");for(int i = 0; i < strArray.length; i++){//空元素，放行if(strArray[i] == null || "".equals(strArray[i]))continue;if(request.getRequestURI().indexOf(strArray[i]) != -1){arg2.doFilter(arg0, arg1);return;}}}if(request.getRequestURI().indexOf("login.jsp") != -1|| request.getRequestURI().indexOf("LoginServlet") != -1){arg2.doFilter(arg0, arg1);return;}if(session.getAttribute("username") != null){arg2.doFilter(arg0, arg1);}else {response.sendRedirect("login.jsp");}}public void init(FilterConfig arg0) throws ServletException {config = arg0;}}

LoginFilter.java

package com.cityhuntshou.servlet;import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;public class LoginServlet extends HttpServlet {/*** Constructor of the object.*/public LoginServlet() {super();}/*** Destruction of the servlet. <br>*/public void destroy() {super.destroy(); // Just puts "destroy" string in log// Put your code here
    }/*** The doGet method of the servlet. <br>** This method is called when a form has its tag value method equals to get.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {}/*** The doPost method of the servlet. <br>** This method is called when a form has its tag value method equals to post.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String username = request.getParameter("username");String password = request.getParameter("password");//new String(username.getBytes("ISO-8859-1"),"UTF-8")
        System.out.println(username);if("admin".equals(username) && "admin".equals(password)){//校验通过HttpSession session = request.getSession();session.setAttribute("username", username);response.sendRedirect(request.getContextPath()+"/success.jsp");}else {//校验失败response.sendRedirect(request.getContextPath()+"/failure.jsp");}}/*** Initialization of the servlet. <br>** @throws ServletException if an error occurs*/public void init() throws ServletException {// Put your code here
    }}

LoginServlet.java

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"><display-name></display-name><servlet><description>This is the description of my J2EE component</description><display-name>This is the display name of my J2EE component</display-name><servlet-name>LoginServlet</servlet-name><servlet-class>com.cityhuntshou.servlet.LoginServlet</servlet-class></servlet><servlet-mapping><servlet-name>LoginServlet</servlet-name><url-pattern>/servlet/LoginServlet</url-pattern></servlet-mapping>    <welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><filter><filter-name>LoginFilter</filter-name><filter-class>com.cityhuntshou.filter.LoginFilter</filter-class><init-param><param-name>noLoginPaths</param-name><param-value>login.jsp;failure.jsp;loginServlet</param-value></init-param><init-param><param-name>charset</param-name><param-value>UTF-8</param-value></init-param></filter><filter-mapping><filter-name>LoginFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>
</web-app>

web.xml

运行效果：

访问结果：

转载于:https://www.cnblogs.com/cityhuntshou/p/7443688.html

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