第十一章過濾器 · javaweb編程

# Filter ## 概念 Filter 的基本功能是對 Servlet 容器調用 Servlet 的過程進行攔截，從而在 Servlet 進行響應處理的前后實現一些特殊的功能。在 Servlet API 中定義了三個接口類來開供開發人員編寫 Filter 程序：Filter, FilterChain, FilterConfig Filter 程序是一個實現了 Filter 接口的 Java 類，與 Servlet 程序相似，它由 Servlet 容器進行調用和執行 Filter 程序需要在 web.xml 文件中進行注冊和設置它所能攔截的資源：Filter 程序可以攔截 Jsp, Servlet, 靜態圖片文件和靜態 html 文件 *** ### 創建一個HelloWorldFilter 創建一個test.jsp 創建一個繼承Filter的類 ~~~ package com.neusoft.web.fiter; 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; public class HelloWorldFilter implements Filter{ @Override public void destroy() { // TODO Auto-generated method stub System.out.println("destroy"); } @Override public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException { // TODO Auto-generated method stub System.out.println("doFilter"); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub System.out.println("init"); } } ~~~ web.xml配置Filter ~~~ <filter> <filter-name>helloworldFilter</filter-name> <filter-class>com.neusoft.web.fiter.HelloWorldFilter</filter-class> </filter> <filter-mapping> <filter-name>helloworldFilter</filter-name> <url-pattern>/20180125/test.jsp</url-pattern> </filter-mapping> ~~~ 運行jsp，發現init()被調用后（創建Filter對象后立即被調用，且只被調用一次），doFilter()被調用，所以init()與Servlet的init()基本功能一樣，都是初始化用的，而doFilter()與Servlet當中的service()功能基本一樣，而FilterConfig與ServletConfig基本一樣，封裝著配置信息；destory()釋放當前Filter所占用的資源的方法，在Filter被銷毀之前調用，且只能調用一次而上述例子當中，發現頁面中的內容并沒有出現，是因為Filter將請求攔截下來了，想要對攔截進行放行，需要調用FilterChain的doFilter方法 ~~~ @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub System.out.println("doFilter"); chain.doFilter(request, response); } ~~~ ### Filter鏈 ~~~ <filter> <filter-name>helloworldFilter</filter-name> <filter-class>com.neusoft.web.fiter.HelloWorldFilter</filter-class> </filter> <filter-mapping> <filter-name>helloworldFilter</filter-name> <url-pattern>/20180125/test.jsp</url-pattern> </filter-mapping> <filter> <filter-name>secondFilter</filter-name> <filter-class>com.neusoft.web.fiter.SecondFilter</filter-class> </filter> <filter-mapping> <filter-name>secondFilter</filter-name> <url-pattern>/20180125/test.jsp</url-pattern> </filter-mapping> ~~~ 多個Filter在一起形成一個Filter鏈，而攔截的順序與filter-mapping的前后有關思考：多個Filter代碼的順序 ~~~ package com.neusoft.web.fiter; 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; public class HelloWorldFilter implements Filter{ @Override public void destroy() { // TODO Auto-generated method stub System.out.println("destroy"); } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub System.out.println("1.doFilter"); chain.doFilter(request, response); System.out.println("2.doFilter"); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub System.out.println("init"); } } ~~~ ~~~ package com.neusoft.web.fiter; 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; public class SecondFilter implements Filter{ @Override public void destroy() { // TODO Auto-generated method stub System.out.println("destroy2"); } @Override public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException { // TODO Auto-generated method stub System.out.println("3.doFilter2"); arg2.doFilter(arg0, arg1); System.out.println("4.doFilter2"); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub System.out.println("init2"); } } ~~~ ~~~ <%@ 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>Insert title here</title> </head> <body> <h1>Test Page</h1> <% System.out.println("5.test"); %> </body> </html> ~~~ *** 課堂練習--1 ![](https://box.kancloud.cn/7ce6f7a537f33c3b95041d24b4101e95_962x656.png) *** #### dispatcher < dispatcher >指定過濾器所攔截的資源被 Servlet 容器調用的方式，可以是REQUEST,INCLUDE,FORWARD和ERROR之一，默認REQUEST. 可以設置多個<dispatcher> 子元素用來指定 Filter 對資源的多種調用方式進行攔截。在filter-mapping中配置。 **REQUEST**：當用戶直接訪問頁面時，Web容器將會調用過濾器。如果目標資源是通過RequestDispatcher的include()或forward()方法訪問時，那么該過濾器就不會被調用。 INCLUDE：如果目標資源是通過RequestDispatcher的include()方法訪問時，那么該過濾器將被調用。除此之外，該過濾器不會被調用。 **FORWARD**：如果目標資源是通過RequestDispatcher的forward()方法訪問時，那么該過濾器將被調用，除此之外，該過濾器不會被調用。 ERROR：如果目標資源是通過聲明式異常處理機制調用時，那么該過濾器將被調用。除此之外，過濾器不會被調用。 *** ### 典型應用1--字符編碼的過濾器在每個頁面上都寫request.setCharacterEncoding()很麻煩，寫個過濾器 one.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>Insert title here</title> </head> <body> <form action="two.jsp" method="post"> username:<input type="text" name="username"> <input type="submit" value="Submit"> </form> </body> </html> ~~~ two.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>Insert title here</title> </head> <body> Hello:${ param.username } </body> </html> ~~~ web.xml ~~~ <context-param> <param-name>encode</param-name> <param-value>UTF-8</param-value> </context-param> ~~~ EncodingFilter ~~~ package com.neusoft.web.fiter; 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.annotation.WebFilter; /** * Servlet Filter implementation class EncodingFilter */ @WebFilter("/*") public class EncodingFilter implements Filter { public void destroy() { // TODO Auto-generated method stub } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { String encode = fConfig.getServletContext().getInitParameter("encode"); request.setCharacterEncoding(encode); chain.doFilter(request, response); } private FilterConfig fConfig; public void init(FilterConfig fConfig) throws ServletException { this.fConfig = fConfig; } } ~~~ *** ### 典型應用2--檢測用戶是否登錄的過濾器 list.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>Insert title here</title> </head> <body> <h1>List Page</h1> <a href="a.jsp">AAA</a> <br><br> <a href="b.jsp">BBB</a> <br><br> <a href="c.jsp">CCC</a> <br><br> <a href="d.jsp">DDD</a> <br><br> <a href="e.jsp">EEE</a> <br><br> </body> </html> ~~~ a.jsp,b.jsp,c.jsp,d.jsp,e.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>Insert title here</title> </head> <body> <h1>BBB Page</h1> <a href="list.jsp">Return...</a> </body> </html> ~~~ doLogin.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>Insert title here</title> </head> <body> <% // 1.獲取用戶的登錄信息 String username = request.getParameter("username"); // 2.若登錄信息完整，則把登錄信息放到HttpSession里 if(username != null && !username.trim().equals("")){ session.setAttribute(application.getInitParameter("userSessionKey"), username); // 3.重定向到list.jsp response.sendRedirect("list.jsp"); }else{ response.sendRedirect("login.jsp"); } %> </body> </html> ~~~ login.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>Insert title here</title> </head> <body> <form action="doLogin.jsp" method="post"> userName:<input type="text" name="username"> <input type="submit" value="Submit"> </form> </body> </html> ~~~ web.xml ~~~  <context-param> <param-name>noCheckPage</param-name> <param-value>/login/a.jsp,/login/doLogin.jsp,/login/list.jsp,/login/login.jsp</param-value> </context-param>  <context-param> <param-name>redirectPage</param-name> <param-value>/login/login.jsp</param-value> </context-param>  <context-param> <param-name>userSessionKey</param-name> <param-value>USERSESSIONKEY</param-value> </context-param> ~~~ CheckLoginFilter ~~~ package com.neusoft.web.fiter; import java.io.IOException; import java.util.Arrays; import java.util.List; 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; /** * Servlet Filter implementation class CheckLoginFilter */ @WebFilter("/login/*") public class CheckLoginFilter extends HttpFilter { private String sessionKey; private String redirectUrl; private String noCheckPage; @Override public void init() { ServletContext servletContext = getFilterConfig().getServletContext(); sessionKey = servletContext.getInitParameter("userSessionKey"); redirectUrl = servletContext.getInitParameter("redirectPage"); // /login/a.jsp,/login/doLogin.jsp,/login/list.jsp,/login/login.jsp noCheckPage = servletContext.getInitParameter("noCheckPage"); } @Override public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws IOException, ServletException { // 1.獲取請求的serlvetPath String servletPath = request.getServletPath(); // 2.檢查獲取到的是否為不需要檢查中的一個，若是，則放行，return List<String> urls = Arrays.asList(noCheckPage.split(",")); if(urls.contains(servletPath)) { filterChain.doFilter(request, response); return; } // 3.檢查是否有登錄者，即檢查sessionKey是否存在，若不存在，則重定向redirectUrl Object user = request.getSession().getAttribute(sessionKey); if(user == null) { response.sendRedirect(request.getContextPath()+redirectUrl); return; } // 4.若存在，放行，允許訪問 filterChain.doFilter(request, response); } } ~~~ HttpFilter ~~~ package com.neusoft.web.fiter; 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; public class HttpFilter implements Filter{ @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain filterChain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest)req; HttpServletResponse response = (HttpServletResponse)res; doFilter(request,response,filterChain); } public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws IOException, ServletException { filterChain.doFilter(request, response); } private FilterConfig filterConfig; public FilterConfig getFilterConfig() { return filterConfig; } @Override public void init(FilterConfig filterConfig) throws ServletException { this.filterConfig = filterConfig; init(); } public void init(){ } } ~~~ *** ### Filter小結（1）簡介 Filter是JavaWEB的一個重要組件，可以對發送到Servlet的請求進行攔截，并對響應也進行攔截 Filter是實現了Filter接口的Java類 Filter需要在web.xml文件中進行配置和映射（注解）（2）在web.xml中如何配置 ~~~ <filter> <filter-name>helloworldFilter</filter-name> <filter-class>com.neusoft.web.fiter.HelloWorldFilter</filter-class> </filter> <filter-mapping> <filter-name>helloworldFilter</filter-name> <url-pattern>/20180125/test.jsp</url-pattern> </filter-mapping> ~~~ 配置與Servlet的配置很相似，url-pattern映射的路徑是可以攔截的資源，也就是通過哪些url能夠訪問到該Filter ***