servlet3.0+規(guī)范后，允許servlet冈涧，filter，listener不必聲明在web.xml中正蛙，而是以硬編碼的方式存在督弓，實現(xiàn)容器的零配置。
ServletContainerInitializer：啟動容器時負責加載相關(guān)配置
package javax.servlet;
import java.util.Set;
public interface ServletContainerInitializer {
public void onStartup(Set<Class<?>> c, ServletContext ctx)
throws ServletException;
}
```
容器啟動時會自動掃描當前服務(wù)中`ServletContainerInitializer`的實現(xiàn)類乒验，并調(diào)用其`onStartup`方法愚隧，其參數(shù)`Set<Class<?>> c`，可通過在實現(xiàn)類上聲明注解`javax.servlet.annotation.HandlesTypes(xxx.class)`注解自動注入锻全，`@HandlesTypes`會自動掃描項目中所有的`xxx.class`的實現(xiàn)類狂塘，并將其全部注入`Set`。
Spring為其提供了一個實現(xiàn)類：
**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);
}
}
}
```
`WebApplicationInitializer`才是需要關(guān)心的接口鳄厌，我們只需要將相應(yīng)的servlet荞胡，filter，listener等硬編碼到該接口的實現(xiàn)類中即可了嚎。
##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>
```
編碼配置：
```
@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為我們提供了一些WebApplicationInitializer的抽象類泪漂，我們只需要繼承并按需修改即可，比如：
**1）****org.springframework.security.web.context.AbstractSecurityWebApplicationInitializer ： SpringSecurity相關(guān)配置**
xml配置：
Xml代碼 [圖片上傳中歪泳。萝勤。。（5）]
<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>
編碼配置：
Java代碼 
@Order(2)
public class WebAppSecurityInitializer extends AbstractSecurityWebApplicationInitializer
{
//servletContext.addListener("org.springframework.security.web.session.HttpSessionEventPublisher");
//session監(jiān)聽器
@Override
protected boolean enableHttpSessionEventPublisher() {
return true;
}
}
**2）org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer：MVC相關(guān)配置呐伞，比如加載spring配置文件敌卓，聲明****DispatcherServlet等等，參看下面的對比：**
xml配置：
Xml代碼 [圖片上傳中荸哟。假哎。瞬捕。（7）]
<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>
編碼方式：
Java代碼 [圖片上傳中。舵抹。肪虎。（8）]
@Order(3)
//spring DispatcherServlet的配置,其它servlet和監(jiān)聽器等需要額外聲明，用@Order注解設(shè)定啟動順序
public class WebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
/*
* DispatcherServlet的映射路徑
*/
@Override
protected String[] getServletMappings() {
return new String[]{"/"};
}
/*
* 應(yīng)用上下文惧蛹，除web部分
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
@Override
protected Class[] getRootConfigClasses() {
//加載配置文件類扇救，這里與上面的xml配置是對應(yīng)的，需要使用@Configuration注解進行標注香嗓，稍后介紹
return new Class[] {AppConfig.class, SpringSecurityConfig.class};
}
/*
* web上下文
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
@Override
protected Class[] getServletConfigClasses() {
return new Class[] {MvcConfig.class};
}
/*
* 注冊過濾器迅腔，映射路徑與DispatcherServlet一致，路徑不一致的過濾器需要注冊到另外的WebApplicationInitializer中
*/
@Override
protected Filter[] getServletFilters() {
CharacterEncodingFilter characterEncodingFilter = new CharacterEncodingFilter();
characterEncodingFilter.setEncoding("UTF-8");
characterEncodingFilter.setForceEncoding(true);
return new Filter[] {characterEncodingFilter};
}
} 