SpringMVC4零配置--web.xml

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

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

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

package org.springframework.web;  
import java.lang.reflect.Modifier;  
import java.util.LinkedList;  
import java.util.List;  
import java.util.ServiceLoader;  
import java.util.Set;  
import javax.servlet.ServletContainerInitializer;  
import javax.servlet.ServletContext;  
import javax.servlet.ServletException;  
import javax.servlet.annotation.HandlesTypes;  
import org.springframework.core.annotation.AnnotationAwareOrderComparator;  
@HandlesTypes(WebApplicationInitializer.class)  
public class SpringServletContainerInitializer implements ServletContainerInitializer {  
        @Override  
    public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)  
            throws ServletException {  
  
        List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();  
  
        if (webAppInitializerClasses != null) {  
            for (Class<?> waiClass : webAppInitializerClasses) {  
                // Be defensive: Some servlet containers provide us with invalid classes,  
                // no matter what @HandlesTypes says...  
                if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&  
                        WebApplicationInitializer.class.isAssignableFrom(waiClass)) {  
                    try {  
                        initializers.add((WebApplicationInitializer) waiClass.newInstance());  
                    }  
                    catch (Throwable ex) {  
                        throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);  
                    }  
                }  
            }  
        }  
  
        if (initializers.isEmpty()) {  
            servletContext.log("No Spring WebApplicationInitializer types detected on classpath");  
            return;  
        }  
  
        AnnotationAwareOrderComparator.sort(initializers);  
        servletContext.log("Spring WebApplicationInitializers detected on classpath: " + initializers);  
  
        for (WebApplicationInitializer initializer : initializers) {  
            initializer.onStartup(servletContext);  
        }  
    }  
  
}  

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：

<!-- Log4jConfigListener -->  
<context-param>  
    <param-name>log4jConfigLocation</param-name>  
    <param-value>classpath:config/properties/log4j.properties</param-value>  
</context-param>  
<listener>  
    <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>  
</listener>  
  
<!-- OpenSessionInViewFilter -->  
<filter>  
    <filter-name>hibernateFilter</filter-name>  
    <filter-class>  
        org.springframework.orm.hibernate4.support.OpenSessionInViewFilter  
    </filter-class>         
</filter>  
<filter-mapping>  
    <filter-name>hibernateFilter</filter-name>  
    <url-pattern>/*</url-pattern>  
</filter-mapping>  
  
<!-- DemoServlet -->  
<servlet>  
    <servlet-name>demoServlet</servlet-name>  
    <servlet-class>web.function.servlet.DemoServlet</servlet-class>  
    <load-on-startup>2</load-on-startup>  
       </servlet>  
<servlet-mapping>  
    <servlet-name>demoServlet</servlet-name>  
    <url-pattern>/demo_servlet</url-pattern>  
</servlet-mapping>  

编码配置：

@Order(1)  
public class CommonInitializer implements WebApplicationInitializer{  
 
   @Override  
   public void onStartup(ServletContext servletContext)  
           throws ServletException {  
         
       //Log4jConfigListener  
       servletContext.setInitParameter("log4jConfigLocation", "classpath:config/properties/log4j.properties");  
       servletContext.addListener(Log4jConfigListener.class);  
         
         
       //OpenSessionInViewFilter  
       OpenSessionInViewFilter hibernateSessionInViewFilter = new OpenSessionInViewFilter();  
       FilterRegistration.Dynamic filterRegistration = servletContext.addFilter(  
               "hibernateFilter", hibernateSessionInViewFilter);  
       filterRegistration.addMappingForUrlPatterns(  
               EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE), false, "/");  
         
         
       //DemoServlet  
       DemoServlet demoServlet = new DemoServlet();  
       ServletRegistration.Dynamic dynamic = servletContext.addServlet(  
               "demoServlet", demoServlet);  
       dynamic.setLoadOnStartup(2);  
       dynamic.addMapping("/demo_servlet");  
                 
         
   }  
}  

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：

<listener>  
    <listener-class>org.springframework.security.web.session.HttpSessionEventPublisher</listener-class>  
</listener>  
 
<filter>  
   <filter-name>springSecurityFilterChain</filter-name>  
   <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>  
</filter>  
 
<filter-mapping>  
   <filter-name>springSecurityFilterChain</filter-name>  
   <url-pattern>/*</url-pattern>  
</filter-mapping>  

编码配置：

@Order(2)  
public class WebAppSecurityInitializer  extends AbstractSecurityWebApplicationInitializer   
{  
   //servletContext.addListener("org.springframework.security.web.session.HttpSessionEventPublisher");  
   //session监听器  
   @Override  
   protected boolean enableHttpSessionEventPublisher() {  
       return true;  
   }  
}  

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：

<context-param>  
   <param-name>contextConfigLocation</param-name>  
   <param-value>  
   classpath:config/context/applicationContext-AppConfig.xml,  
   classpath:config/context/applicationContext-SpringSecurityConfig.xml  
   </param-value>  
</context-param>  
 
<listener>  
   <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>  
</listener>  
 
<filter>  
   <filter-name>Set Character Encoding</filter-name>  
   <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>  
   <init-param>  
       <param-name>encoding</param-name>  
       <param-value>UTF-8</param-value>  
   </init-param>  
   <init-param>  
       <param-name>forceEncoding</param-name>  
       <param-value>true</param-value>  
   </init-param> 
</filter>  
 
<filter-mapping>  
   <filter-name>Set Character Encoding</filter-name>  
   <url-pattern>/*</url-pattern>  
</filter-mapping>  
 
<servlet>  
   <servlet-name>webmvc</servlet-name>  
   <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>  
   <init-param>  
       <param-name>contextConfigLocation</param-name>  
       <param-value>classpath:config/context/applicationContext-MvcConfig.xml</param-value>  
   </init-param>  
   <load-on-startup>1</load-on-startup>  
</servlet>  
 
<servlet-mapping>  
   <servlet-name>webmvc</servlet-name>  
   <url-pattern>/</url-pattern>  
</servlet-mapping>  

编码方式：

@Order(3)  
//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  
public class WebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {  
   /* 
     * DispatcherServlet的映射路径 
     */  
   @Override  
   protected String[] getServletMappings() {  
       return new String[]{"/"};  
   }  
  
   /* 
     * 应用上下文，除web部分 
     */  
   @SuppressWarnings({ "unchecked", "rawtypes" })  
   @Override  
   protected Class[] getRootConfigClasses() {  
       //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  
       return new Class[] {AppConfig.class, SpringSecurityConfig.class};  
   }  
  
   /* 
     * web上下文 
     */  
   @SuppressWarnings({ "unchecked", "rawtypes" })  
   @Override  
   protected Class[] getServletConfigClasses() {  
       return new Class[] {MvcConfig.class};  
   }  
  
   /* 
     * 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 
     */  
   @Override  
   protected Filter[] getServletFilters() {  
       CharacterEncodingFilter characterEncodingFilter = new CharacterEncodingFilter();  
       characterEncodingFilter.setEncoding("UTF-8");  
       characterEncodingFilter.setForceEncoding(true);  
       return new Filter[] {characterEncodingFilter};  
   }     
 
}