spring boot中如何启动tomcat或jetty的

柔光的暖阳◎ 2021-12-11 08:21 351阅读 0赞

最近面试中会聊到这个话题，说实话之前已经做过大量spring boot源码级的分享，如果你在之前看过[Spring Boot 容器启动原理揭秘][Spring Boot]，想必已经有了一个大概的认识。启动tomcat或jetty其实也跳不出这个套路，或者讲它仅仅是其中的一个环节，通过AbstractApplicationContext.onRefresh()完成的。

**知识回顾**

Spring Boot的一个及其吸引人的特性是fat-jar技术，解下`jar`解压包的`MANIFEST.MF文件我们会发现Main-Class`及Start-Class，而Start-Class就是我们程序中的`main`函数类`DemoApplication。`

![20190709221004906.png][]

**SpringApplication**

而这个启动类中重点关注SpringApplication类，有两个非常重要的方法：

*  private void initialize(Object\[\] sources)
 *  public static ConfigurableApplicationContext run(Object source, String... args)

public class SpringApplication {
        public SpringApplication(Object... sources) {
            this.bannerMode = Mode.CONSOLE;
            this.logStartupInfo = true;
            this.addCommandLineProperties = true;
            this.headless = true;
            this.registerShutdownHook = true;
            this.additionalProfiles = new HashSet();
            this.initialize(sources);//关注点
        }
        //初始化启动参数变量
        private void initialize(Object[] sources) {
            if (sources != null && sources.length > 0) {
                this.sources.addAll(Arrays.asList(sources));
            }
    
            this.webEnvironment = this.deduceWebEnvironment();
            this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
            this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
            this.mainApplicationClass = this.deduceMainApplicationClass();
        }
        //启动ioc容器与tomcat容器
        public static ConfigurableApplicationContext run(Object source, String... args) {
            return run(new Object[]{source}, args);
        }
        public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
            return (new SpringApplication(sources)).run(args);
        }
        //run真正执行的方法
        public ConfigurableApplicationContext run(String... args) {
            StopWatch stopWatch = new StopWatch();
            stopWatch.start();
            ConfigurableApplicationContext context = null;
            FailureAnalyzers analyzers = null;
            this.configureHeadlessProperty();
            SpringApplicationRunListeners listeners = this.getRunListeners(args);
            listeners.starting();
    
            try {
                ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
                ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
                Banner printedBanner = this.printBanner(environment);
                //创建ioc容器
                context = this.createApplicationContext();
                new FailureAnalyzers(context);
                this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
                //刷新ioc容器上下文
                this.refreshContext(context);
                this.afterRefresh(context, applicationArguments);
                listeners.finished(context, (Throwable)null);
                stopWatch.stop();
                if (this.logStartupInfo) {
                    (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
                }
    
                return context;
            } catch (Throwable var9) {
                this.handleRunFailure(context, listeners, (FailureAnalyzers)analyzers, var9);
                throw new IllegalStateException(var9);
            }
        }
        private void refreshContext(ConfigurableApplicationContext context) {
            this.refresh(context);//此次很关键
            if (this.registerShutdownHook) {
                try {
                    context.registerShutdownHook();
                } catch (AccessControlException var3) {
                    ;
                }
            }
    
        }
        protected void refresh(ApplicationContext applicationContext) {
            Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
            //这个一定不陌生吧
            ((AbstractApplicationContext)applicationContext).refresh();
        }
        //会创建ioc为AnnotationConfigEmbeddedWebApplicationContext
        protected ConfigurableApplicationContext createApplicationContext() {
            Class<?> contextClass = this.applicationContextClass;
            if (contextClass == null) {
                try {
                    contextClass = Class.forName(this.webEnvironment ? "org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext" : "org.springframework.context.annotation.AnnotationConfigApplicationContext");
                } catch (ClassNotFoundException var3) {
                    throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
                }
            }
    
            return (ConfigurableApplicationContext)BeanUtils.instantiate(contextClass);
        }
    }

要解答本文的疑问，问题有回到了AbstractApplicationContext.refresh()，如果你对它里面干的事情比较熟悉的话，后续可以不用继续看下去了。

**AbstractApplicationContext.refresh()**

它主要是通过工厂类EmbeddedServletContainerFactory生成一个EmbeddedServletContainer实例，再调用start方法进行启动，最终完成tomcat、jetty的启动。

public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext, DisposableBean {
        //ioc的最重要的一些组件
    	@Override
    	public void refresh() throws BeansException, IllegalStateException {
    		synchronized (this.startupShutdownMonitor) {
    			// Prepare this context for refreshing.
    			prepareRefresh();
    
    			// Tell the subclass to refresh the internal bean factory.
    			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
    			// Prepare the bean factory for use in this context.
    			prepareBeanFactory(beanFactory);
    
    			try {
    				// Allows post-processing of the bean factory in context subclasses.
    				postProcessBeanFactory(beanFactory);
    
    				// Invoke factory processors registered as beans in the context.
    				invokeBeanFactoryPostProcessors(beanFactory);
    
    				// Register bean processors that intercept bean creation.
    				registerBeanPostProcessors(beanFactory);
    
    				// Initialize message source for this context.
    				initMessageSource();
    
    				// Initialize event multicaster for this context.
    				initApplicationEventMulticaster();
    
    				// Initialize other special beans in specific context subclasses.
    				onRefresh();//重点关注这里
    
    				// Check for listener beans and register them.
    				registerListeners();
    
    				// Instantiate all remaining (non-lazy-init) singletons.
    				finishBeanFactoryInitialization(beanFactory);
    
    				// Last step: publish corresponding event.
    				finishRefresh();//重点关注这里
    			}
    
    			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.
    				destroyBeans();
    
    				// Reset 'active' flag.
    				cancelRefresh(ex);
    
    				// Propagate exception to caller.
    				throw ex;
    			}
    
    			finally {
    				// Reset common introspection caches in Spring's core, since we
    				// might not ever need metadata for singleton beans anymore...
    				resetCommonCaches();
    			}
    		}
    	}
    	protected void onRefresh() throws BeansException {//没错，实现在子类中
    		// For subclasses: do nothing by default.
    	}
    }
    public class AnnotationConfigEmbeddedWebApplicationContext extends EmbeddedWebApplicationContext {
    }
    public class EmbeddedWebApplicationContext extends GenericWebApplicationContext {
        //重写了AbstractApplicationContext的onRefresh
        protected void onRefresh() {
            super.onRefresh();
    
            try {
                this.createEmbeddedServletContainer();//看名字是不是有种柳暗花明的感觉
            } catch (Throwable var2) {
                throw new ApplicationContextException("Unable to start embedded container", var2);
            }
        }
        //没错就是创建tomcat的核心类EmbeddedServletContainer
        private void createEmbeddedServletContainer() {
            EmbeddedServletContainer localContainer = this.embeddedServletContainer;
            ServletContext localServletContext = this.getServletContext();
            if (localContainer == null && localServletContext == null) {
                EmbeddedServletContainerFactory containerFactory = this.getEmbeddedServletContainerFactory();
                this.embeddedServletContainer = containerFactory.getEmbeddedServletContainer(new ServletContextInitializer[]{this.getSelfInitializer()});
            } else if (localServletContext != null) {
                try {
                    this.getSelfInitializer().onStartup(localServletContext);
                } catch (ServletException var4) {
                    throw new ApplicationContextException("Cannot initialize servlet context", var4);
                }
            }
    
            this.initPropertySources();
        }
        //获取Sevlet工程中获取web容器
        protected EmbeddedServletContainerFactory getEmbeddedServletContainerFactory() {
            String[] beanNames = this.getBeanFactory().getBeanNamesForType(EmbeddedServletContainerFactory.class);
            if (beanNames.length == 0) {
                throw new ApplicationContextException("Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.");
            } else if (beanNames.length > 1) {
                throw new ApplicationContextException("Unable to start EmbeddedWebApplicationContext due to multiple EmbeddedServletContainerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames));
            } else {
                return (EmbeddedServletContainerFactory)this.getBeanFactory().getBean(beanNames[0], EmbeddedServletContainerFactory.class);
            }
        }
        //重写了AbstractApplicationContext的finishRefresh
        protected void finishRefresh() {
            super.finishRefresh();
            //关注点
            EmbeddedServletContainer localContainer = this.startEmbeddedServletContainer();
            if (localContainer != null) {
                this.publishEvent(new EmbeddedServletContainerInitializedEvent(this, localContainer));
            }
    
        }
        //启动tomcat
        private EmbeddedServletContainer startEmbeddedServletContainer() {
            EmbeddedServletContainer localContainer = this.embeddedServletContainer;
            if (localContainer != null) {
                localContainer.start();//start方法
            }
    
            return localContainer;
        }
    }

**EmbeddedServletContainerFactory**

此时你觉得EmbeddedServletContainerFactory有点突兀，它从哪里来，又是做什么的呢？首先看它的实现：

*  TomcatEmbeddedServletContainerFactory，tomcat容器
 *  JettyEmbeddedServletContainerFactory，Jetty容器
 *  UndertowEmbeddedServletContainerFactory，Undertow容器

它来自spring的SPI（spring.factories），Auto Configure的配置key=EnableAutoConfiguration

![20190709224443803.png][]

![20190709224746145.png][]

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
    @Configuration
    @ConditionalOnWebApplication
    @Import(BeanPostProcessorsRegistrar.class)
    public class EmbeddedServletContainerAutoConfiguration {
    
    	/**
    	 * Nested configuration if Tomcat is being used.
    	 */
    	@Configuration
    	@ConditionalOnClass({ Servlet.class, Tomcat.class })
    	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    	public static class EmbeddedTomcat {
    
    		@Bean
    		public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {//这就是为什么可以在ioc中可以获取了
    			return new TomcatEmbeddedServletContainerFactory();
    		}
    
    	}
    
    	/**
    	 * Nested configuration if Jetty is being used.
    	 */
    	@Configuration
    	@ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
    			WebAppContext.class })
    	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    	public static class EmbeddedJetty {
    
    		@Bean
    		public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
    			return new JettyEmbeddedServletContainerFactory();
    		}
    
    	}
    
    	/**
    	 * Nested configuration if Undertow is being used.
    	 */
    	@Configuration
    	@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
    	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    	public static class EmbeddedUndertow {
    
    		@Bean
    		public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
    			return new UndertowEmbeddedServletContainerFactory();
    		}
    
    	}
    }
    public class TomcatEmbeddedServletContainerFactory extends AbstractEmbeddedServletContainerFactory implements ResourceLoaderAware {
        private static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
        private static final Set<Class<?>> NO_CLASSES = Collections.emptySet();
        public static final String DEFAULT_PROTOCOL = "org.apache.coyote.http11.Http11NioProtocol";
        private File baseDirectory;
        private List<Valve> engineValves = new ArrayList();
        private List<Valve> contextValves = new ArrayList();
        private List<LifecycleListener> contextLifecycleListeners = new ArrayList();
        private List<TomcatContextCustomizer> tomcatContextCustomizers = new ArrayList();
        private List<TomcatConnectorCustomizer> tomcatConnectorCustomizers = new ArrayList();
        private List<Connector> additionalTomcatConnectors = new ArrayList();
        private ResourceLoader resourceLoader;
        private String protocol = "org.apache.coyote.http11.Http11NioProtocol";
        private Set<String> tldSkipPatterns;
        private Charset uriEncoding;
        private int backgroundProcessorDelay;
    
        public TomcatEmbeddedServletContainerFactory() {
            this.tldSkipPatterns = new LinkedHashSet(TldSkipPatterns.DEFAULT);
            this.uriEncoding = DEFAULT_CHARSET;
        }
        //上面的调用：创建Tomcat的容器
        public EmbeddedServletContainer getEmbeddedServletContainer(ServletContextInitializer... initializers) {
            Tomcat tomcat = new Tomcat();
            File baseDir = this.baseDirectory != null ? this.baseDirectory : this.createTempDir("tomcat");
            tomcat.setBaseDir(baseDir.getAbsolutePath());
            Connector connector = new Connector(this.protocol);
            tomcat.getService().addConnector(connector);
            this.customizeConnector(connector);
            tomcat.setConnector(connector);
            tomcat.getHost().setAutoDeploy(false);
            this.configureEngine(tomcat.getEngine());
            Iterator var5 = this.additionalTomcatConnectors.iterator();
    
            while(var5.hasNext()) {
                Connector additionalConnector = (Connector)var5.next();
                tomcat.getService().addConnector(additionalConnector);
            }
    
            this.prepareContext(tomcat.getHost(), initializers);
            return this.getTomcatEmbeddedServletContainer(tomcat);
        }
    }
    //Tomcat的容器
    public class TomcatEmbeddedServletContainer implements EmbeddedServletContainer {
        public TomcatEmbeddedServletContainer(Tomcat tomcat, boolean autoStart) {
            this.monitor = new Object();
            this.serviceConnectors = new HashMap();
            Assert.notNull(tomcat, "Tomcat Server must not be null");
            this.tomcat = tomcat;
            this.autoStart = autoStart;
            this.initialize();//关键点
        }
        //tomcat初始化
        private void initialize() throws EmbeddedServletContainerException {
            logger.info("Tomcat initialized with port(s): " + this.getPortsDescription(false));
            Object var1 = this.monitor;
            synchronized(this.monitor) {
                try {
                    this.addInstanceIdToEngineName();
    
                    try {
                        final Context context = this.findContext();
                        context.addLifecycleListener(new LifecycleListener() {
                            public void lifecycleEvent(LifecycleEvent event) {
                                if (context.equals(event.getSource()) && "start".equals(event.getType())) {
                                    TomcatEmbeddedServletContainer.this.removeServiceConnectors();
                                }
    
                            }
                        });
                        this.tomcat.start();
                        this.rethrowDeferredStartupExceptions();
    
                        try {
                            ContextBindings.bindClassLoader(context, this.getNamingToken(context), this.getClass().getClassLoader());
                        } catch (NamingException var5) {
                            ;
                        }
    
                        this.startDaemonAwaitThread();
                    } catch (Exception var6) {
                        containerCounter.decrementAndGet();
                        throw var6;
                    }
                } catch (Exception var7) {
                    this.stopSilently();
                    throw new EmbeddedServletContainerException("Unable to start embedded Tomcat", var7);
                }
    
            }
        }
        //启动方法
        public void start() throws EmbeddedServletContainerException {
            Object var1 = this.monitor;
            synchronized(this.monitor) {
                if (!this.started) {
                    boolean var10 = false;
    
                    try {
                        var10 = true;
                        this.addPreviouslyRemovedConnectors();
                        Connector var2 = this.tomcat.getConnector();
                        if (var2 != null && this.autoStart) {
                            this.performDeferredLoadOnStartup();
                        }
    
                        this.checkThatConnectorsHaveStarted();
                        this.started = true;
                        logger.info("Tomcat started on port(s): " + this.getPortsDescription(true));
                        var10 = false;
                    } catch (ConnectorStartFailedException var11) {
                        this.stopSilently();
                        throw var11;
                    } catch (Exception var12) {
                        throw new EmbeddedServletContainerException("Unable to start embedded Tomcat servlet container", var12);
                    } finally {
                        if (var10) {
                            Context context = this.findContext();
                            ContextBindings.unbindClassLoader(context, this.getNamingToken(context), this.getClass().getClassLoader());
                        }
                    }
    
                    Context context = this.findContext();
                    ContextBindings.unbindClassLoader(context, this.getNamingToken(context), this.getClass().getClassLoader());
                }
            }
        }
    }

Spring Boot里面知识点其实是非常多的，很多时候我们在研究源码的时候，一定要大胆猜测，最后通过调试来完成最终的验证。![94594375][]

[Spring Boot]: https://blog.csdn.net/alex_xfboy/article/details/88194392
[20190709221004906.png]: /images/20211211/20fd921b377c405592d41a1310b71e2e.png
[20190709224443803.png]: /images/20211211/7c8d96b9cf2f47e38e3f14dc123ac62b.png
[20190709224746145.png]: /images/20211211/a1f86f1df1084b77ae62106e57f1a21c.png
[94594375]: /images/20211211/4bc5b48007dd497d9781519c94759e9d.png