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?
如圖所示,對于一個指定了過濾器的Web資源(Servlet、JSP、HTML)來說,過濾器攔在客戶端與Web資源之間,進出都要經過過濾器。
當請求到來時,先經過過濾器,過濾器可以檢查、修改請求的內容再發給對應的Web資源,甚至可以根據請求的內容禁止客戶端訪問對應的Web資源。
Web資源產生的應答也要先經過過濾器,過濾器可以檢查、修改應答的內容再發給客戶端。
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Filter接口
過濾器必須實現javax.servlet.Filter接口,這個接口包含3個方法:init、doFilter、destroy。
init(FilterConfig filterConfig) :Java EE容器創建過濾器實例后調用這個方法,用于為過濾器做準備工作,可以從filterConfig對象讀取配置文件web.xml中為該過濾器設置的初始化參數。
doFilter(ServletRequest request, ServletResponse response, FilterChain chain) :過濾操作在這個方法里實現,包括檢查、修改請求對象,檢查修改應答對象。參數request是請求對象,response是應答對象,chain用于訪問后續過濾器。
destroy() :Java EE容器在銷毀過濾器實例前調用這個方法,用于釋放資源。
<?xml version="1.0" encoding="UTF-8"?> <web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> <display-name>myweb</display-name> <filter> <filter-name>filter1</filter-name> <filter-class>hb.filter.Filter1</filter-class> </filter> <filter-mapping> <filter-name>filter1</filter-name> <url-pattern>/filter/*</url-pattern> </filter-mapping> <filter> <filter-name>filter2</filter-name> <filter-class>hb.filter.Filter2</filter-class> </filter> <filter-mapping> <filter-name>filter2</filter-name> <url-pattern>/filter/*</url-pattern> </filter-mapping> </web-app>?
package hb.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; public class Filter1 implements Filter { public void destroy() { System.out.println("Filter1 destory"); } public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain chain) throws IOException, ServletException { System.out.println("Filter1 doFilter"); chain.doFilter(arg0, arg1); } public void init(FilterConfig arg0) throws ServletException { System.out.println("Filter1 init"); } }?
package hb.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; public class Filter2 implements Filter{ public void destroy() { System.out.println("Filter2 destory"); } public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException { System.out.println("Filter2 doFilter"); } public void init(FilterConfig arg0) throws ServletException { System.out.println("Filter2 init"); } }?
<filter> <filter-name>myFilter</filter-name> <filter-class>xx.MyFilter</filte-class> </filter> <filter-mapping> <filter-name>myFilter</filter-name> <servlet-name>目標資源一</servlet-name> <dispatcher>REQUEST</dispatcher> </filter-mapping> <filter-mapping> <filter-name>myFilter</filter-name> <servlet-name>目標資源二</servlet-name> <dispatcher>REQUEST</dispatcher> </filter-mapping>?
<?xml version="1.0" encoding="UTF-8"?> <web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> <display-name>myweb</display-name> <servlet> <display-name>MyServlet</display-name> <servlet-name>MyServlet</servlet-name> <servlet-class>hb.filter.MyServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>/MyServlet.do</url-pattern> </servlet-mapping> <filter> <filter-name>filter3</filter-name> <filter-class>hb.filter.Filter3</filter-class> </filter> <filter-mapping> <filter-name>filter3</filter-name> <servlet-name>MyServlet</servlet-name> </filter-mapping> </web-app>?
package hb.filter; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class MyServlet extends HttpServlet { private static final long serialVersionUID = 1L; public MyServlet() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("servlet"); response.sendRedirect("index.jsp"); } }?
package hb.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; public class Filter3 implements Filter { public void destroy() { System.out.println("Filter3 destory"); } public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain chain) throws IOException, ServletException { System.out.println("Filter3 doFilter"); chain.doFilter(arg0, arg1);//不能少,否則無法到servlet處理 } public void init(FilterConfig arg0) throws ServletException { System.out.println("Filter3 init"); } }?
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