Springboot 2使用外部Tomcat源码分析

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-tomcat</artifactId>
  <scope>provided</scope>
</dependency>

@SpringBootApplication
public class Bootstrap extends SpringBootServletInitializer {
 public static void main(String[] args) {
  SpringApplication.run(Bootstrap.class, args);
 }
 @Override
 protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
  return builder.sources(Bootstrap.class);
 }
}

// 容器启动时，将 WebApplicationInitializer 的所有子类传递至 webAppInitializerClasses
@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
  /**
   * @param webAppInitializerClasses @HandlesTypes 导入的类
   * @param servletContext 当前 web 应用 servlet 上下文
   */
  @Override
  public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException {
    List<WebApplicationInitializer> initializers = new LinkedList<>();
    for (Class<?> waiClass : webAppInitializerClasses) {
      // 过滤出可用的 WebApplicationInitializer
      if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) && WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
        initializers.add((WebApplicationInitializer)ReflectionUtils.accessibleConstructor(waiClass).newInstance());
      }
    }
    for (WebApplicationInitializer initializer : initializers) {
      initializer.onStartup(servletContext);
    }
  }
}

public void onStartup(ServletContext servletContext) throws ServletException {
  WebApplicationContext rootAppContext = createRootApplicationContext(servletContext);
}
protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) {
  SpringApplicationBuilder builder = createSpringApplicationBuilder();
  // 指定主类 Bootstrap
  builder.main(getClass());
  // 回调 Bootstrap 重写的方法
  builder = configure(builder);
  return run(builder.build());
}