web.xml

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servlet3.0+规范后，允许servlet，filter，listener不必声明在web.xml中，而是以硬编码的方式存在，实现容器的零配置。

ServletContainerInitializer：启动容器时负责加载相关配置

Java代码  

1. package javax.servlet;  
2. import java.util.Set;  
3. public interface ServletContainerInitializer {  
4.  public void onStartup(Set<Class<?>> c, ServletContext ctx)  
5.         throws ServletException;   
6. }  

 容器启动时会自动扫描当前服务中ServletContainerInitializer的实现类，并调用其onStartup方法，其参数Set<Class<?>> c，可通过在实现类上声明注解javax.servlet.annotation.HandlesTypes(xxx.class)注解自动注入，@HandlesTypes会自动扫描项目中所有的xxx.class的实现类，并将其全部注入Set。

Spring为其提供了一个实现类：

SpringServletContainerInitializer

Java代码  

1. package org.springframework.web;  
2. import java.lang.reflect.Modifier;  
3. import java.util.LinkedList;  
4. import java.util.List;  
5. import java.util.ServiceLoader;  
6. import java.util.Set;  
7. import javax.servlet.ServletContainerInitializer;  
8. import javax.servlet.ServletContext;  
9. import javax.servlet.ServletException;  
10. import javax.servlet.annotation.HandlesTypes;  
11. import org.springframework.core.annotation.AnnotationAwareOrderComparator;  
12. @HandlesTypes(WebApplicationInitializer.class)  
13. public class SpringServletContainerInitializer implements ServletContainerInitializer {  
14.         @Override  
15.     public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)  
16.             throws ServletException {  
17.   
18.         List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();  
19.   
20.         if (webAppInitializerClasses != null) {  
21.             for (Class<?> waiClass : webAppInitializerClasses) {  
22.                 // Be defensive: Some servlet containers provide us with invalid classes,  
23.                 // no matter what @HandlesTypes says...  
24.                 if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&  
25.                         WebApplicationInitializer.class.isAssignableFrom(waiClass)) {  
26.                     try {  
27.                         initializers.add((WebApplicationInitializer) waiClass.newInstance());  
28.                     }  
29.                     catch (Throwable ex) {  
30.                         throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);  
31.                     }  
32.                 }  
33.             }  
34.         }  
35.   
36.         if (initializers.isEmpty()) {  
37.             servletContext.log("No Spring WebApplicationInitializer types detected on classpath");  
38.             return;  
39.         }  
40.   
41.         AnnotationAwareOrderComparator.sort(initializers);  
42.         servletContext.log("Spring WebApplicationInitializers detected on classpath: " + initializers);  
43.   
44.         for (WebApplicationInitializer initializer : initializers) {  
45.             initializer.onStartup(servletContext);  
46.         }  
47.     }  
48.   
49. }  

 从中可以看出，WebApplicationInitializer才是我们需要关心的接口，我们只需要将相应的servlet，filter，listener等硬编码到该接口的实现类中即可。比如：

xml配置：

Xml代码  

1.        <!-- Log4jConfigListener -->  
2.        <context-param>  
3.     <param-name>log4jConfigLocation</param-name>  
4.     <param-value>classpath:config/properties/log4j.properties</param-value>  
5.        </context-param>  
6.        <listener>  
7.     <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>  
8.        </listener>  
9.   
10.        <!-- OpenSessionInViewFilter -->  
11.        <filter>  
12.     <filter-name>hibernateFilter</filter-name>  
13.     <filter-class>  
14.         org.springframework.orm.hibernate4.support.OpenSessionInViewFilter  
15.     </filter-class>         
16.        </filter>  
17.        <filter-mapping>  
18.     <filter-name>hibernateFilter</filter-name>  
19.     <url-pattern>/*</url-pattern>  
20.        </filter-mapping>  
21.   
22.        <!-- DemoServlet -->  
23.        <servlet>  
24.     <servlet-name>demoServlet</servlet-name>  
25.     <servlet-class>web.function.servlet.DemoServlet</servlet-class>  
26.     <load-on-startup>2</load-on-startup>  
27.        </servlet>  
28. <servlet-mapping>  
29.     <servlet-name>demoServlet</servlet-name>  
30.     <url-pattern>/demo_servlet</url-pattern>  
31. </servlet-mapping>  

 编码配置：

Java代码  

1. @Order(1)  
2. public class CommonInitializer implements WebApplicationInitializer{  
3.   
4.     @Override  
5.     public void onStartup(ServletContext servletContext)  
6.             throws ServletException {  
7.           
8.         //Log4jConfigListener  
9.         servletContext.setInitParameter("log4jConfigLocation", "classpath:config/properties/log4j.properties");  
10.         servletContext.addListener(Log4jConfigListener.class);  
11.           
12.           
13.         //OpenSessionInViewFilter  
14.         OpenSessionInViewFilter hibernateSessionInViewFilter = new OpenSessionInViewFilter();  
15.         FilterRegistration.Dynamic filterRegistration = servletContext.addFilter(  
16.                 "hibernateFilter", hibernateSessionInViewFilter);  
17.         filterRegistration.addMappingForUrlPatterns(  
18.                 EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE), false, "/");  
19.           
20.           
21.         //DemoServlet  
22.         DemoServlet demoServlet = new DemoServlet();  
23.         ServletRegistration.Dynamic dynamic = servletContext.addServlet(  
24.                 "demoServlet", demoServlet);  
25.         dynamic.setLoadOnStartup(2);  
26.         dynamic.addMapping("/demo_servlet");  
27.                   
28.           
29.     }  
30.   
31.       
32. }  

Spring为我们提供了一些WebApplicationInitializer的抽象类，我们只需要继承并按需修改即可，比如：

1）org.springframework.security.web.context.AbstractSecurityWebApplicationInitializer ： SpringSecurity相关配置

xml配置：

Xml代码  

1.        <listener>  
2.     <listener-class>org.springframework.security.web.session.HttpSessionEventPublisher</listener-class>  
3. </listener>  
4.   
5.        <filter>  
6.     <filter-name>springSecurityFilterChain</filter-name>  
7.     <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>  
8. </filter>  
9.   
10.        <filter-mapping>  
11.     <filter-name>springSecurityFilterChain</filter-name>  
12.     <url-pattern>/*</url-pattern>  
13. </filter-mapping>  

编码配置：

Java代码  

1. @Order(2)  
2. public class WebAppSecurityInitializer  extends AbstractSecurityWebApplicationInitializer   
3. {  
4.     //servletContext.addListener("org.springframework.security.web.session.HttpSessionEventPublisher");  
5.     //session监听器  
6.     @Override  
7.     protected boolean enableHttpSessionEventPublisher() {  
8.         return true;  
9.     }  
10. }  

2）org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer：MVC相关配置，比如加载spring配置文件，声明DispatcherServlet等等，参看下面的对比：

xml配置：

Xml代码  

1.        <context-param>  
2.     <param-name>contextConfigLocation</param-name>  
3.     <param-value>  
4.     classpath:config/context/applicationContext-AppConfig.xml,  
5.     classpath:config/context/applicationContext-SpringSecurityConfig.xml  
6.         </param-value>  
7. </context-param>  
8.   
9.        <listener>  
10.     <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>  
11. </listener>  
12.   
13.        <filter>  
14.     <filter-name>Set Character Encoding</filter-name>  
15.     <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>  
16.     <init-param>  
17.         <param-name>encoding</param-name>  
18.         <param-value>UTF-8</param-value>  
19.     </init-param>  
20.     <init-param>  
21.         <param-name>forceEncoding</param-name>  
22.         <param-value>true</param-value>  
23.     </init-param>  
24. </filter>  
25.   
26.        <filter-mapping>  
27.     <filter-name>Set Character Encoding</filter-name>  
28.     <url-pattern>/*</url-pattern>  
29. </filter-mapping>  
30.   
31.        <servlet>  
32.     <servlet-name>webmvc</servlet-name>  
33.     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>  
34.     <init-param>  
35.         <param-name>contextConfigLocation</param-name>  
36.         <param-value>classpath:config/context/applicationContext-MvcConfig.xml</param-value>  
37.     </init-param>  
38.     <load-on-startup>1</load-on-startup>  
39. </servlet>  
40.   
41. <servlet-mapping>  
42.     <servlet-name>webmvc</servlet-name>  
43.     <url-pattern>/</url-pattern>  
44. </servlet-mapping>  

编码方式：

Java代码  

1. @Order(3)  
2. //spring DispatcherServlet的配置,其它servlet和监听器等需要额外声明，用@Order注解设定启动顺序  
3. public class WebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {  
4.     /* 
5.       * DispatcherServlet的映射路径 
6.       */  
7.     @Override  
8.     protected String[] getServletMappings() {  
9.         return new String[]{"/"};  
10.     }  
11.    
12.     /* 
13.       * 应用上下文，除web部分 
14.       */  
15.     @SuppressWarnings({ "unchecked", "rawtypes" })  
16.     @Override  
17.     protected Class[] getRootConfigClasses() {  
18.         //加载配置文件类，这里与上面的xml配置是对应的，需要使用@Configuration注解进行标注，稍后介绍  
19.         return new Class[] {AppConfig.class, SpringSecurityConfig.class};  
20.     }  
21.    
22.     /* 
23.       * web上下文 
24.       */  
25.     @SuppressWarnings({ "unchecked", "rawtypes" })  
26.     @Override  
27.     protected Class[] getServletConfigClasses() {  
28.         return new Class[] {MvcConfig.class};  
29.     }  
30.    
31.     /* 
32.       * 注册过滤器，映射路径与DispatcherServlet一致，路径不一致的过滤器需要注册到另外的WebApplicationInitializer中 
33.       */  
34.     @Override  
35.     protected Filter[] getServletFilters() {  
36.         CharacterEncodingFilter characterEncodingFilter = new CharacterEncodingFilter();  
37.         characterEncodingFilter.setEncoding("UTF-8");  
38.         characterEncodingFilter.setForceEncoding(true);  
39.         return new Filter[] {characterEncodingFilter};  
40.     }     
41.   
42. }  

web.xml

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原文地址：http://www.cnblogs.com/yhtboke/p/5764690.html