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};
}
}
