一、Servlet 3 扩展接口

1.1、ServletContainerInitializer 容器初始化接口

  • 主要用于在容器启动阶段通过编程风格注册Filter、Servlet以及Listener，以取代通过web.xml配置注册

    1. public interface ServletContainerInitializer {
    3.   public void onStartup(Set<Class<?>> c, ServletContext ctx)
    4.       throws ServletException; 
    5. }

    1.2、指定初始化类的注解 HandlesTypes

    ```java @Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) public @interface HandlesTypes {

    //指定初始化的类 Class<?>[] value(); }

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  2. ### 1.3、原理
  4. - Tomcat 启动时，通过SPI 机制，找到在路径META-INF/services/javax.servlet.ServletContainerInitializer下定义的初始化类，并实例化
  5. - 通过注解 @HandlesTypes 获取到自定义的初始化类
  6. - 执行调用 ServletContainerInitializer#onStartup
  7. - 执行链路

StandardContext #startInternal() —> StandardContext父类LifecycleBase#fireLifecycleEvent(Lifecycle.CONFIGURE_START_EVENT, null); —> //LifecycleListener 实现ContextConfig ContextConfig#lifecycleEvent(event)
—> ContextConfig #configureStart(); —> ContextConfig #webConfig(); —> ContextConfig #processServletContainerInitializers —> //加载完，保存到 StandardContext#initializers中 WebappServiceLoader#load(Class serviceType) —> 遍历StandardContext#initializers，执行ServletContainerInitializer

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  2. ## 二、纯 Java SpringMVC 配置
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  4. ### 2.1、实现WebApplicationInitializer
  5. ```java
  6. public class MyWebApplicationInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
  9.     /**
  10.      * Spring Root上下文配置
  11.      *
  12.      * @return
  13.      */
  14.     protected Class<?>[] getRootConfigClasses() {
  15.         return new Class[]{RootConfig.class};
  16.     }
  19.     /**
  20.      * SpringMVC 配置
  21.      *
  22.      * @return
  23.      */
  24.     protected Class<?>[] getServletConfigClasses() {
  25.         return new Class[]{WebMvcConfig.class};
  26.     }
  28.     /**
  29.      * MVC 映射路径
  30.      *
  31.      * @return
  32.      */
  33.     protected String[] getServletMappings() {
  34.         return new String[]{
  35.                 "/*"
  36.         };
  37.     }
  38. }

2.2、Root配置

  1. @Configuration
  2. @ComponentScan(value = "cn.hdj.mvc", excludeFilters = {
  3.         //排除扫描 controller
  4.         @ComponentScan.Filter(type = FilterType.ANNOTATION, classes = {Controller.class})
  5. })
  6. public class RootConfig {
  7. }

2.3、MVC 配置

  1. @Configuration
  2. @ComponentScan(value = "cn.hdj.mvc.modules",
  3.         includeFilters = {
  4.                 @ComponentScan.Filter(type = FilterType.ANNOTATION, classes = {Controller.class})
  5.         }, useDefaultFilters = false)
  6. @EnableWebMvc
  7. public class WebMvcConfig  extends WebMvcConfigurerAdapter {
  9.     /**
  10.      * 配置视图解析器
  11.      *
  12.      * @return
  13.      */
  14.     @Bean
  15.     public ViewResolver viewResolver() {
  16.         InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
  17.         viewResolver.setPrefix("/WEB-INF/view/");
  18.         viewResolver.setSuffix(".jsp");
  19.         return viewResolver;
  20.     }
  22.     /**
  23.      *    <!-- 配置静态资源用WEB容器默认的servlet来处理 -->
  24.      *     <mvc:default-servlet-handler/>
  25.      * @param configurer
  26.      */
  27.     @Override
  28.     public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
  29.         configurer.enable();
  30.     }
  31. }

2.4、Spring 的ServletContainerInitializer 实现

2.4.1、在 mvc jar包中定义ServletContainerInitializer

  • 文件路径 ``` META-INF\services\javax.servlet.ServletContainerInitializer

//文件内容 org.springframework.web.SpringServletContainerInitializer

  2. - SpringServletContainerInitializer
  3. ```java
  4. @HandlesTypes(WebApplicationInitializer.class)
  5. public class SpringServletContainerInitializer implements ServletContainerInitializer {
  7.     @Override
  8.     public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
  9.             throws ServletException {
  11.         List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>();
  13.         if (webAppInitializerClasses != null) {
  14.             for (Class<?> waiClass : webAppInitializerClasses) {
  15.                 // Be defensive: Some servlet containers provide us with invalid classes,
  16.                 // no matter what @HandlesTypes says...
  17.                 if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
  18.                         WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
  19.                     try {
  20.                         //实例化 WebApplicationInitializer
  21.                         initializers.add((WebApplicationInitializer) waiClass.newInstance());
  22.                     }
  23.                     catch (Throwable ex) {
  24.                         throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
  25.                     }
  26.                 }
  27.             }
  28.         }
  30.         if (initializers.isEmpty()) {
  31.             servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
  32.             return;
  33.         }
  35.         servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
  36.         AnnotationAwareOrderComparator.sort(initializers);
  37.         for (WebApplicationInitializer initializer : initializers) {
  38.             //调用 WebApplicationInitializer
  39.             initializer.onStartup(servletContext);
  40.         }
  41.     }
  43. }

三、SpringMVC Java Config 启动整体过程

  • Tomcat 启动时，通过SPI 机制，找到在路径META-INF/services/javax.servlet.ServletContainerInitializer下定义的初始化类，并实例化
  • 通过注解 @HandlesTypes 获取到自定义的初始化类
  • 执行调用 ServletContainerInitializer#onStartup
  • 在 SpringServletContainerInitializer#onStartup中创建 ContextLoaderListener，并设置到ServletContext中
  • 执行 ContextLoaderListener 监听器，初始化 Spring 上下文

四、简单内嵌Tomcat启动

4.1、添加依赖

  2.         <dependency>
  3.             <groupId>javax.servlet</groupId>
  4.             <artifactId>javax.servlet-api</artifactId>
  5.             <version>3.1.0</version>
  6.         </dependency>
  8.         <!-- https://mvnrepository.com/artifact/org.apache.tomcat.embed/tomcat-embed-core -->
  9.         <dependency>
  10.             <groupId>org.apache.tomcat.embed</groupId>
  11.             <artifactId>tomcat-embed-core</artifactId>
  12.             <version>8.5.81</version>
  13.         </dependency>
  14.         <!-- https://mvnrepository.com/artifact/org.apache.tomcat.embed/tomcat-embed-jasper -->
  15.         <dependency>
  16.             <groupId>org.apache.tomcat.embed</groupId>
  17.             <artifactId>tomcat-embed-jasper</artifactId>
  18.             <version>8.5.81</version>
  19.         </dependency>

4.2、启动

  2. public class MvcJavaConfigApplication {
  4.     public static void main(String[] args) throws LifecycleException {
  5.         Tomcat tomcat = new Tomcat();
  6.         Server server = tomcat.getServer();
  7.         Service service = tomcat.getService();
  8.         service.setName("Tomcat-embbeded");
  9.         Connector connector = new Connector("HTTP/1.1");
  10.         connector.setPort(8080);
  11.         service.addConnector(connector);
  12.         //应用目录
  13.         tomcat.addWebapp("", System.getProperty("user.dir") + File.separator);
  14.         server.start();
  15.         System.out.println("tomcat服务器启动成功..");
  16.         System.out.println("http://127.0.0.1:8080");
  17.         server.await();
  18.     }
  19. }

项目Demo