SpringBoot嵌入式tomcat源码剖析

1、入口

跟SpringBoot 源码分析刷新应用上下文(3)-refreshContext

这个篇文章一样的入口，一直到

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
            // 准备刷新此上下文
			prepareRefresh();
 
			// Tell the subclass to refresh the internal bean factory.
            // 告诉子类刷新内部bean工厂
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
 
			// Prepare the bean factory for use in this context.
            // 准备bean工厂以便在此上下文中使用。
			prepareBeanFactory(beanFactory);
 
			try {
				// Allows post-processing of the bean factory in context subclasses.
                // 允许在上下文子类中对bean工厂进行后处理
				postProcessBeanFactory(beanFactory);
 
				// Invoke factory processors registered as beans in the context.
                // 调用在上下文中注册为bean的工厂处理器
				invokeBeanFactoryPostProcessors(beanFactory);
 
				// Register bean processors that intercept bean creation.
                // 注册拦截bean创建的bean处理器
				registerBeanPostProcessors(beanFactory);
 
				// Initialize message source for this context.
                // 初始化此上下文的消息源
				initMessageSource();
 
				// Initialize event multicaster for this context.
                // 初始化此上下文的事件多播
				initApplicationEventMulticaster();
 
				// Initialize other special beans in specific context subclasses.
                // 初始化特定上下文子类中的其他特殊bean
				onRefresh();
 
				// Check for listener beans and register them.
                // 检查侦听器bean并注册它们
				registerListeners();
 
				// Instantiate all remaining (non-lazy-init) singletons.
                // 实例化所有剩余的（非惰性init）singleton
				finishBeanFactoryInitialization(beanFactory);
 
				// Last step: publish corresponding event.
                // 最后一步：发布相应的事件
				finishRefresh();
			}
 
			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}
 
				// Destroy already created singletons to avoid dangling resources.
                // 销毁已创建的singleton以避免挂起资源
				destroyBeans();
 
				// Reset 'active' flag.
                // 重置“活动”标志
				cancelRefresh(ex);
 
				// Propagate exception to caller.
                // 向调用方传播异常
				throw ex;
			}
 
			finally {
				// Reset common introspection caches in Spring's core, since we
                // 重置Spring核心中的常见内省缓存，因为我们
				// might not ever need metadata for singleton beans anymore...
                // 可能不再需要单例bean的元数据了。。。
				resetCommonCaches();
			}
		}
	}

这里查看 onRefresh(); 方法

截图：

代码：

/**
	 * Template method which can be overridden to add context-specific refresh work.
     * 可以重写以添加上下文特定刷新工作的模板方法。
	 * Called on initialization of special beans, before instantiation of singletons.
     * 在初始化特殊 bean 时调用，在实例化 singleton 之前调用
	 * 
This implementation is empty. -- 此实现为空
	 * @throws BeansException in case of errors
	 * @see #refresh()
	 */
	protected void onRefresh() throws BeansException {
		// For subclasses: do nothing by default.
	}

 找到其具体类的实现方法 ServeltWebServerApplicationContext

截图：

代码：

@Override
	protected void onRefresh() {
		super.onRefresh();
		try {
            // 核心方法，会获取嵌入的 Servlet 对象，并通过工厂获取 Servlet 容器
			createWebServer();
		}
		catch (Throwable ex) {
			throw new ApplicationContextException("Unable to start web server", ex);
		}
	}

接着看其实现方法 createWebServer()

截图：

 

 代码：

private void createWebServer() {
		WebServer webServer = this.webServer;
		ServletContext servletContext = getServletContext();
		if (webServer == null && servletContext == null) {
            // 先获取 Servlet 容器工厂对象
			ServletWebServerFactory factory = getWebServerFactory();
            // getSelfInitializer() 这个方法在 完成 springMVC 的自动装配的时候会用到
			this.webServer = factory.getWebServer(getSelfInitializer());
		}
		else if (servletContext != null) {
			try {
				getSelfInitializer().onStartup(servletContext);
			}
			catch (ServletException ex) {
				throw new ApplicationContextException("Cannot initialize servlet context", ex);
			}
		}
		initPropertySources();
	}

 接着看 红框中 this.webServer = factory.getWebServer(getSelfInitializer());方法

截图：

是一个接口，接着找到其具体实现类 TomcatServletWebServerFactory

 

截图：

 

代码：

@Override
	public WebServer getWebServer(ServletContextInitializer... initializers) {
		if (this.disableMBeanRegistry) {
			Registry.disableRegistry();
		}
        //实例化一个 Tomcat
		Tomcat tomcat = new Tomcat();
		File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
        //设置 Tomcat 的工作临时目录
		tomcat.setBaseDir(baseDir.getAbsolutePath());
        // 进行 Tomcat 实例对象的各种配置信息
		Connector connector = new Connector(this.protocol); 
		connector.setThrowOnFailure(true);
        //个体 Service 添加 Connector
		tomcat.getService().addConnector(connector);
		customizeConnector(connector);
		tomcat.setConnector(connector);
        // 关闭热部署
		tomcat.getHost().setAutoDeploy(false);
        // 配置 Engine
		configureEngine(tomcat.getEngine());
		for (Connector additionalConnector : this.additionalTomcatConnectors) {
			tomcat.getService().addConnector(additionalConnector);
		}
		prepareContext(tomcat.getHost(), initializers);
        // 实例化 TomcatWebServer 时会将 DespatcherServlet 以及一些 Filter 添加到 Tomcat 中
		return getTomcatWebServer(tomcat);
	}

 

 接着看红框的方法  getTomcatWebServer(tomcat)

截图：

代码：

/**
	 * Factory method called to create the {@link TomcatWebServer}. Subclasses can
	 * override this method to return a different {@link TomcatWebServer} or apply
	 * additional processing to the Tomcat server.
     * 为创建 TomcatWebServe 而调用的 Factory 方法。子类可以覆盖此方法以返回不同的 TomcatWebServe 或者 对 Tomcat 服务器应用额外的处理
	 * @param tomcat the Tomcat server.
	 * @return a new {@link TomcatWebServer} instance -- 一个新的 TomcatWebServe 实例
	 */
	protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
		return new TomcatWebServer(tomcat, getPort() >= 0);
	}

 

接着查看 TomcatWebServer 的构造方法

 代码：

/**
	 * Create a new {@link TomcatWebServer} instance.
	 * @param tomcat the underlying Tomcat server
	 * @param autoStart if the server should be started
	 */
	public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
		Assert.notNull(tomcat, "Tomcat Server must not be null");
		this.tomcat = tomcat;
		this.autoStart = autoStart;
		initialize();
	}

接着看 initialize() 方法

截图：

代码：

private void initialize() throws WebServerException {
		logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
		synchronized (this.monitor) {
			try {
				addInstanceIdToEngineName();

				Context context = findContext();
				context.addLifecycleListener((event) -> {
					if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
						// Remove service connectors so that protocol binding doesn't
                        // 删除服务连接器，这样协议绑定就不会
						// happen when the service is started.
                        // 当服务启动时发生
						removeServiceConnectors();
					}
				});

				// Start the server to trigger initialization listeners
                // 启动服务器以触发初始化侦听器
				this.tomcat.start();

				// We can re-throw failure exception directly in the main thread
                // 我们可以直接在主线程中重新抛出失败异常
				rethrowDeferredStartupExceptions();

				try {
					ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
				}
				catch (NamingException ex) {
					// Naming is not enabled. Continue
                    // 未启用命名。持续
				}

				// Unlike Jetty, all Tomcat threads are daemon threads. We create a
                // 与Jetty不同，所有Tomcat线程都是守护进程线程。我们创建
				// blocking non-daemon to stop immediate shutdown
                // 阻止非后台进程以停止立即关闭
				startDaemonAwaitThread();
			}
			catch (Exception ex) {
				stopSilently();
				destroySilently();
				throw new WebServerException("Unable to start embedded Tomcat", ex);
			}
		}
	}