filter的执行顺序

一直没有仔细去研究下filter ，最近系统的测试了下：

先看代码吧

1. FirstFilter.java
2. ==================
3. package com.test.filter;
4. import java.io.IOException;
5. import javax.servlet.Filter;
6. import javax.servlet.FilterChain;
7. import javax.servlet.FilterConfig;
8. import javax.servlet.ServletException;
9. import javax.servlet.ServletRequest;
10. import javax.servlet.ServletResponse;
11. public class FirstFilter implements Filter {
12. @Override
13. public void destroy() {
14. }
15. @Override
16. public void doFilter(ServletRequest request, ServletResponse response,
17. FilterChain chain) throws IOException, ServletException {
18. System.out.println("before invoke firstFilter's chain.doFilter() ..");
19. chain.doFilter(request, response);
20. System.out.println("after invoke firstFilter's chain.doFilter() ..");
21. }
22. @Override
23. public void init(FilterConfig arg0) throws ServletException {
24. System.out.println("firstFilter init()...");
25. }
26. }
27. ============
28. SecondFilter.java
29. ==============
30. package com.test.filter;
31. import java.io.IOException;
32. import javax.servlet.Filter;
33. import javax.servlet.FilterChain;
34. import javax.servlet.FilterConfig;
35. import javax.servlet.ServletException;
36. import javax.servlet.ServletRequest;
37. import javax.servlet.ServletResponse;
38. public class SecondFilter implements Filter {
39. @Override
40. public void destroy() {
41. }
42. @Override
43. public void doFilter(ServletRequest request, ServletResponse response,
44. FilterChain chain) throws IOException, ServletException {
45. System.out.println("before invoke secondFilter's chain.doFilter() ..");
46. chain.doFilter(request, response);
47. System.out.println("after invoke secondFilter's chain.doFilter() ..");
48. }
49. @Override
50. public void init(FilterConfig filterConfig) throws ServletException {
51. System.out.println("secondFilter init()...");
52. }
53. }
54. ==========
55. FirstServlet.java
56. =============
57. package com.test.servlet;
58. import java.io.IOException;
59. import javax.servlet.ServletException;
60. import javax.servlet.http.HttpServlet;
61. import javax.servlet.http.HttpServletRequest;
62. import javax.servlet.http.HttpServletResponse;
63. public class FirstServlet extends HttpServlet {
64. @Override
65. protected void doGet(HttpServletRequest req, HttpServletResponse resp)
66. throws ServletException, IOException {
67. System.out.println("servlet doGet be invoked...");
68. req.getRequestDispatcher("test.jsp").forward(req, resp);
69. }
70. @Override
71. protected void doPost(HttpServletRequest req, HttpServletResponse resp)
72. throws ServletException, IOException {
73. // TODO Auto-generated method stub
74. doGet(req, resp);
75. }
76. }
77. =========
78. web.xml
79. ===========
80. <?xml version="1.0" encoding="UTF-8"?>
81. <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
82. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
83. xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
84. http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
85. <welcome-file-list>
86. <welcome-file>index.jsp</welcome-file>
87. </welcome-file-list>
88. <filter>
89. <filter-name>firstFilter</filter-name>
90. <filter-class>com.test.filter.FirstFilter</filter-class>
91. </filter>
92. <filter>
93. <filter-name>secondFilter</filter-name>
94. <filter-class>com.test.filter.SecondFilter</filter-class>
95. </filter>
96. <filter-mapping>
97. <filter-name>secondFilter</filter-name>
98. <url-pattern>/*</url-pattern>
99. </filter-mapping>
100. <filter-mapping>
101. <filter-name>firstFilter</filter-name>
102. <url-pattern>/*</url-pattern>
103. </filter-mapping>
104. <servlet>
105. <servlet-name>firstServlet</servlet-name>
106. <servlet-class>com.alimama.servlet.FirstServlet</servlet-class>
107. </servlet>
108. <servlet-mapping>
109. <servlet-name>firstServlet</servlet-name>
110. <url-pattern>/firstServlet</url-pattern>
111. </servlet-mapping>
112. </web-app>
113. ============

然后发布，发现打印的日志如下：

。。。

firstFilter init()...
secondFilter init()...

。。。

2008-10-23 11:36:43 org.apache.catalina.startup.Catalina start
信息: Server startup in 3665 ms

这里过滤器初始化好了。

当我们访问我们的 应用：http://127.0.0.1:8080/appName

发现打印日记如下：

before invoke secondFilter's chain.doFilter() ..
before invoke firstFilter's chain.doFilter() ..
after invoke firstFilter's chain.doFilter() ..
after invoke secondFilter's chain.doFilter() ..

当我们将web.xml中filter的位置进行调整后：

1. <?xml version="1.0" encoding="UTF-8"?>
2. <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
3. xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4. xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
5. http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
6. <welcome-file-list>
7. <welcome-file>index.jsp</welcome-file>
8. </welcome-file-list>
9. <filter>
10. <filter-name>firstFilter</filter-name>
11. <filter-class>com.test.filter.FirstFilter</filter-class>
12. </filter>
13. <filter>
14. <filter-name>secondFilter</filter-name>
15. <filter-class>com.test.filter.SecondFilter</filter-class>
16. </filter>
17. <filter-mapping>
18. <filter-name>firstFilter</filter-name>
19. <url-pattern>/*</url-pattern>
20. </filter-mapping>
21. <filter-mapping>
22. <filter-name>secondFilter</filter-name>
23. <url-pattern>/*</url-pattern>
24. </filter-mapping></span>
25. <servlet>
26. <servlet-name>firstServlet</servlet-name>
27. <servlet-class>com.alimama.servlet.FirstServlet</servlet-class>
28. </servlet>
29. <servlet-mapping>
30. <servlet-name>firstServlet</servlet-name>
31. <url-pattern>/firstServlet</url-pattern>
32. </servlet-mapping>
33. </web-app>

然后在启动应用，会看到打印：

before invoke firstFilter's chain.doFilter() ..

before invoke secondFilter's chain.doFilter() ..
after invoke secondFilter's chain.doFilter() ..

after invoke firstFilter's chain.doFilter() ..

总结：

filter的执行顺序是按照web.xml中定义的顺序进行执行的（当多个filter都匹配的时候）。