SpringBoot嵌入式Tomcat的自動配置原理

時間  2019-12-19
標籤 springboot 嵌入 tomcat 自動 配置 原理 欄目 Spring 简体版
原文   原文鏈接

在讀本篇文章以前若是你讀過這篇文章SpringBoot自動裝配原理解析應該會更加輕鬆web

準備工做

咱們知道SpringBoot的自動裝配的祕密在org.springframework.boot.autoconfigure包下的spring.factories文件中，而嵌入Tomcat的原理就在這個文件中加載的一個配置類：org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfigurationspring

@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@ConditionalOnClass(ServletRequest.class)
@ConditionalOnWebApplication(type = Type.SERVLET)
@EnableConfigurationProperties(ServerProperties.class)
@Import({ ServletWebServerFactoryAutoConfiguration.BeanPostProcessorsRegistrar.class,
		ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
		ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
		ServletWebServerFactoryConfiguration.EmbeddedUndertow.class })
public class ServletWebServerFactoryAutoConfiguration {

	@Bean
	public ServletWebServerFactoryCustomizer servletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new ServletWebServerFactoryCustomizer(serverProperties);
	}

	@Bean
	@ConditionalOnClass(name = "org.apache.catalina.startup.Tomcat")
	public TomcatServletWebServerFactoryCustomizer tomcatServletWebServerFactoryCustomizer(
			ServerProperties serverProperties) {
		return new TomcatServletWebServerFactoryCustomizer(serverProperties);
	}

	/**
	 * Registers a {@link WebServerFactoryCustomizerBeanPostProcessor}. Registered via
	 * {@link ImportBeanDefinitionRegistrar} for early registration.
	 */
	public static class BeanPostProcessorsRegistrar
			implements ImportBeanDefinitionRegistrar, BeanFactoryAware {

		private ConfigurableListableBeanFactory beanFactory;

		@Override
		public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
			if (beanFactory instanceof ConfigurableListableBeanFactory) {
				this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
			}
		}

		@Override
		public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
				BeanDefinitionRegistry registry) {
			if (this.beanFactory == null) {
				return;
			}
			registerSyntheticBeanIfMissing(registry,
					"webServerFactoryCustomizerBeanPostProcessor",
					WebServerFactoryCustomizerBeanPostProcessor.class);
			registerSyntheticBeanIfMissing(registry,
					"errorPageRegistrarBeanPostProcessor",
					ErrorPageRegistrarBeanPostProcessor.class);
		}

		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry,
				String name, Class<?> beanClass) {
			if (ObjectUtils.isEmpty(
					this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
				beanDefinition.setSynthetic(true);
				registry.registerBeanDefinition(name, beanDefinition);
			}
		}

	}

}

首先看一下上方的幾個註解apache

  1. @AutoConfigureOrder這個註解是決定配置類的加載順序的，當註解裏的值越小越先加載，而Ordered.HIGHEST_PRECEDENCE的值是Integer.MIN_VALUE也就是說這個類確定是最早加載的那一批
  2. @ConditionalOnXXX在以前的文章中已經無數次提到了，就再也不闡述了
  3. @EnableConfigurationProperties開啓ServerProperties類的屬性值配置。而這個類裏面包含的就是Web服務的配置
@ConfigurationProperties(prefix = "server", ignoreUnknownFields = true)
public class ServerProperties {

	private Integer port;

	private InetAddress address;

	@NestedConfigurationProperty
	private final ErrorProperties error = new ErrorProperties();

	private Boolean useForwardHeaders;

	private String serverHeader;

	private int maxHttpHeaderSize = 0; // bytes

	private Duration connectionTimeout;

	@NestedConfigurationProperty
	private Ssl ssl;

	@NestedConfigurationProperty
	private final Compression compression = new Compression();

	@NestedConfigurationProperty
	private final Http2 http2 = new Http2();

	private final Servlet servlet = new Servlet();

	private final Tomcat tomcat = new Tomcat();

	private final Jetty jetty = new Jetty();

	private final Undertow undertow = new Undertow();
}

這個類的代碼太多了，這裏就不一一貼出來了，咱們日常在application.properties中配置的server.xxx就是這個類中屬性 4. @Import引入了4個類，看都是什麼吧tomcat

  1. BeanPostProcessorsRegistrar
public static class BeanPostProcessorsRegistrar
			implements ImportBeanDefinitionRegistrar, BeanFactoryAware {
		@Override
		public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
				BeanDefinitionRegistry registry) {
			if (this.beanFactory == null) {
				return;
			}
			registerSyntheticBeanIfMissing(registry,
					"webServerFactoryCustomizerBeanPostProcessor",
					WebServerFactoryCustomizerBeanPostProcessor.class);
			registerSyntheticBeanIfMissing(registry,
					"errorPageRegistrarBeanPostProcessor",
					ErrorPageRegistrarBeanPostProcessor.class);
		}

		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry,
				String name, Class<?> beanClass) {
			if (ObjectUtils.isEmpty(
					this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
				beanDefinition.setSynthetic(true);
				registry.registerBeanDefinition(name, beanDefinition);
			}
		}

	}

這個類註冊了兩個bean：WebServerFactoryCustomizerBeanPostProcessor和ErrorPageRegistrarBeanPostProcessor關於這兩個bean的做用稍後再詳細介紹 2. EmbeddedTomcatapp

@Configuration
	@ConditionalOnClass({ Servlet.class, Tomcat.class, UpgradeProtocol.class })
	@ConditionalOnMissingBean(value = ServletWebServerFactory.class, search = SearchStrategy.CURRENT)
	public static class EmbeddedTomcat {

		@Bean
		public TomcatServletWebServerFactory tomcatServletWebServerFactory() {
			return new TomcatServletWebServerFactory();
		}

	}

這個類會在存在Tomcat相關jar包時添加一個TomcatServletWebServerFactorybeanide

其餘兩個相信你們都知道怎麼回事了post

  1. 除了這些這個類還注入了兩個類ServletWebServerFactoryCustomizer和TomcatServletWebServerFactoryCustomizer

如今前期準備工做已經作好了，看一下這個Tomcat是如何啓動的吧this

啓動

啓動入口在ServletWebServerApplicationContext中的onRefresh方法code

protected void onRefresh() {
		super.onRefresh();
		try {
			createWebServer();
		}
		catch (Throwable ex) {
			throw new ApplicationContextException("Unable to start web server", ex);
		}
	}

Tomcat的啓動就在createWebServer方法裏面了server

private void createWebServer() {
		WebServer webServer = this.webServer;
		ServletContext servletContext = getServletContext();
  		//第一次訪問的時候兩個對象都爲空
		if (webServer == null && servletContext == null) {
			ServletWebServerFactory factory = getWebServerFactory();
			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();
	}

首先看一下getWebServerFactory

protected ServletWebServerFactory getWebServerFactory() {
		// 這裏獲取的beanname就是上方註冊的tomcatServletWebServerFactory了
		String[] beanNames = getBeanFactory()
				.getBeanNamesForType(ServletWebServerFactory.class);
		if (beanNames.length == 0) {
			throw new ApplicationContextException(
					"Unable to start ServletWebServerApplicationContext due to missing "
							+ "ServletWebServerFactory bean.");
		}
		if (beanNames.length > 1) {
			throw new ApplicationContextException(
					"Unable to start ServletWebServerApplicationContext due to multiple "
							+ "ServletWebServerFactory beans : "
							+ StringUtils.arrayToCommaDelimitedString(beanNames));
		}
		return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
	}

準備環境裏註冊的bean如今出來一個了。注意，上方還註冊了一個後置處理器EmbeddedServletContainerCustomizerBeanPostProcessor，獲取beantomcatServletWebServerFactory的時候就會執行後置處理器的postProcessBeforeInitialization方法

public Object postProcessBeforeInitialization(Object bean, String beanName)
			throws BeansException {
	if (bean instanceof WebServerFactory) {
		postProcessBeforeInitialization((WebServerFactory) bean);
	}
	return bean;
}
private void postProcessBeforeInitialization(WebServerFactory webServerFactory) {
		LambdaSafe
				.callbacks(WebServerFactoryCustomizer.class, getCustomizers(),
						webServerFactory)
				.withLogger(WebServerFactoryCustomizerBeanPostProcessor.class)
				.invoke((customizer) -> customizer.customize(webServerFactory));
	}

	private Collection<WebServerFactoryCustomizer<?>> getCustomizers() {
		if (this.customizers == null) {
			// Look up does not include the parent context
			this.customizers = new ArrayList<>(getWebServerFactoryCustomizerBeans());
			this.customizers.sort(AnnotationAwareOrderComparator.INSTANCE);
			this.customizers = Collections.unmodifiableList(this.customizers);
		}
		return this.customizers;
	}

	@SuppressWarnings({ "unchecked", "rawtypes" })
	private Collection<WebServerFactoryCustomizer<?>> getWebServerFactoryCustomizerBeans() {
		return (Collection) this.beanFactory
				.getBeansOfType(WebServerFactoryCustomizer.class, false, false).values();
	}

這個處理器的做用是得到全部定製器，而後執行定製器的方法

接着往下看

這個時候就能夠啓動Tomcat了

public WebServer getWebServer(ServletContextInitializer... initializers) {
		Tomcat tomcat = new Tomcat();
		File baseDir = (this.baseDirectory != null ? this.baseDirectory
				: createTempDir("tomcat"));
		tomcat.setBaseDir(baseDir.getAbsolutePath());
		Connector connector = new Connector(this.protocol);
		tomcat.getService().addConnector(connector);
		customizeConnector(connector);
		tomcat.setConnector(connector);
		tomcat.getHost().setAutoDeploy(false);
		configureEngine(tomcat.getEngine());
		for (Connector additionalConnector : this.additionalTomcatConnectors) {
			tomcat.getService().addConnector(additionalConnector);
		}
		prepareContext(tomcat.getHost(), initializers);
		return getTomcatWebServer(tomcat);
	}
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
		return new TomcatWebServer(tomcat, getPort() >= 0);
	}
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
		Assert.notNull(tomcat, "Tomcat Server must not be null");
		this.tomcat = tomcat;
		this.autoStart = autoStart;
		initialize();
	}
private void initialize() throws WebServerException {
		TomcatWebServer.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
						// happen when the service is started.
						removeServiceConnectors();
					}
				});

				// Start the server to trigger initialization listeners
				this.tomcat.start();

				// We can re-throw failure exception directly in the main thread
				rethrowDeferredStartupExceptions();

				try {
					ContextBindings.bindClassLoader(context, context.getNamingToken(),
							getClass().getClassLoader());
				}
				catch (NamingException ex) {
					// Naming is not enabled. Continue
				}

				// Unlike Jetty, all Tomcat threads are daemon threads. We create a
				// blocking non-daemon to stop immediate shutdown
				startDaemonAwaitThread();
			}
			catch (Exception ex) {
				throw new WebServerException("Unable to start embedded Tomcat", ex);
			}
		}
	}

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