java-過濾器Filter_多個Filter的執行順序


http://www.cnblogs.com/HigginCui/p/5772514.html

【Filter鏈】

*在一個web應用中,可以開發編寫多個Filter,這些Filter組合起來稱為一個Filter鏈。

*web服務器根據Filter在web.xml中的注冊順序,決定先調用哪個Filter,當第一個Filter的doFilter方法被調用時,web服務器會創建一個代表Filter鏈的FilterChain對象傳遞給該方法,在doFilter方法中,開發人員如果調用了FilterChain對象的doFilter方法,則web服務器會檢查FilterChain對象中是否還有filter,如果有,則調用第二個filter,如果沒有,則調用目標資源。

 

【工程截圖】

設計了兩個Filter和一個Servlet,訪問Servlet時,查看Filter的執行順序。

【web.xml】

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<?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" id="WebApp_ID" version="3.0"> <display-name>FilterDemo01</display-name> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <!-- 過濾順序:誰的寫在上面,誰先被過濾 --> <filter> <filter-name>FilterTest01</filter-name> <filter-class>com.Higgin.web.filter.FilterTest01</filter-class> </filter> <filter-mapping> <filter-name>FilterTest01</filter-name> <url-pattern>/*</url-pattern> <!-- 過濾所有 --> </filter-mapping> <filter> <filter-name>FilterTest02</filter-name> <filter-class>com.Higgin.web.filter.FilterTest02</filter-class> </filter> <filter-mapping> <filter-name>FilterTest02</filter-name> <url-pattern>/*</url-pattern> <!-- 過濾所有 --> </filter-mapping> </web-app>
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【FilterTest01.java】

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package com.Higgin.web.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 FilterTest01 implements Filter{ @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {  System.out.println("FilterTest01 執行前---");  chain.doFilter(request, response);//讓目標資源執行,即:放行  System.out.println("FilterTest01 執行后---"); } @Override public void init(FilterConfig arg0) throws ServletException { } @Override public void destroy() { } }
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【FilterTest02.java】

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package com.Higgin.web.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 FilterTest02 implements Filter{ @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {  System.out.println("FilterTest02 執行前---"); chain.doFilter(request, response); //放行 System.out.println("FilterTest02 執行后---"); } @Override public void init(FilterConfig arg0) throws ServletException { } @Override public void destroy() { } }
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【ServletTest01.java】

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package com.Higgin.web.servlet; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class ServletTest01 */ @WebServlet("/ServletTest01") public class ServletTest01 extends HttpServlet { private static final long serialVersionUID = 1L; public ServletTest01() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //response.getWriter().write("中國 加油!China Come on!"); System.out.println("執行ServletTest01---"); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } }
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【運行結果】

在瀏覽器中輸入:http://localhost:8080/FilterDemo01/ServletTest01

查看控制台輸出結果

 

自己可以嘗試分別注釋FilterTest01和FilterTest02中的chain.doFilter方法,用Junit查看具體的執行過程。


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