SpringMVC4零配置--web.xml

weixin_34248705發表於2015-08-18
SpringMVCWebXML

servlet3.0+規範後，允許servlet，filter，listener不必宣告在web.xml中，而是以硬編碼的方式存在，實現容器的零配置。

ServletContainerInitializer：啟動容器時負責載入相關配置

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中ServletContainerInitializer的實現類，並呼叫其onStartup方法，其引數Set<Class<?>> c，可通過在實現類上宣告註解javax.servlet.annotation.HandlesTypes(xxx.class)註解自動注入，@HandlesTypes會自動掃描專案中所有的xxx.class的實現類，並將其全部注入Set。

Spring為其提供了一個實現類：

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);  
        }  
    }  
  
}

從中可以看出，WebApplicationInitializer才是我們需要關心的介面，我們只需要將相應的servlet，filter，listener等硬編碼到該介面的實現類中即可。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>

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，我們只需要繼承並按需修改即可，比如：
1）****org.springframework.security.web.context.AbstractSecurityWebApplicationInitializer ： SpringSecurity相關配置

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>

編碼配置：

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

2）org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer：MVC相關配置，比如載入spring配置檔案，宣告****DispatcherServlet等等，參看下面的對比：

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>

編碼方式：

@Order(3)  
//spring DispatcherServlet的配置,其它servlet和監聽器等需要額外宣告，用@Order註解設定啟動順序  
public class WebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {  
   /* 
     * DispatcherServlet的對映路徑 
     */  
   @Override  
   protected String[] getServletMappings() {  
       return new String[]{"/"};  
   }  
  
   /* 
     * 應用上下文，除web部分 
     */  
   @SuppressWarnings({ "unchecked", "rawtypes" })  
   @Override  
   protected Class[] getRootConfigClasses() {  
       //載入配置檔案類，這裡與上面的xml配置是對應的，需要使用@Configuration註解進行標註，稍後介紹  
       return new Class[] {AppConfig.class, SpringSecurityConfig.class};  
   }  
  
   /* 
     * web上下文 
     */  
   @SuppressWarnings({ "unchecked", "rawtypes" })  
   @Override  
   protected Class[] getServletConfigClasses() {  
       return new Class[] {MvcConfig.class};  
   }  
  
   /* 
     * 註冊過濾器，對映路徑與DispatcherServlet一致，路徑不一致的過濾器需要註冊到另外的WebApplicationInitializer中 
     */  
   @Override  
   protected Filter[] getServletFilters() {  
       CharacterEncodingFilter characterEncodingFilter = new CharacterEncodingFilter();  
       characterEncodingFilter.setEncoding("UTF-8");  
       characterEncodingFilter.setForceEncoding(true);  
       return new Filter[] {characterEncodingFilter};  
   }     
 
}

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