spring boot 2.0 源码分析（五）

在上一篇文章中我们详细分析了spring boot是如何准备上下文环境的，今天我们来看一下run函数剩余的内容。还是先把run函数贴出来：

	/**
	 * Run the Spring application, creating and refreshing a new
	 * {@link ApplicationContext}.
	 * @param args the application arguments (usually passed from a Java main method)
	 * @return a running {@link ApplicationContext}
	 */
	public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(
					args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(
					SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
			prepareContext(context, environment, listeners, applicationArguments,
					printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass)
						.logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

我们接着往下看，来看一下this.refreshContext(context);函数，这个函数用于刷新上下文，跟踪到源码看一下：

	private void refreshContext(ConfigurableApplicationContext context) {
		refresh(context);
		if (this.registerShutdownHook) {
			try {
				context.registerShutdownHook();
			}
			catch (AccessControlException ex) {
				// Not allowed in some environments.
			}
		}
	}

在refreshContext函数中，第一行调用了refresh(context);跳转了一下，下面的代码是注册了一个应用关闭的函数钩子。

先来看refresh(context);函数：

	/**
	 * Refresh the underlying {@link ApplicationContext}.
	 * @param applicationContext the application context to refresh
	 */
	protected void refresh(ApplicationContext applicationContext) {
		Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
		((AbstractApplicationContext) applicationContext).refresh();
	}

通过代码跟踪分析发现，其实是调用了AbstractApplicationContext中的refresh方法。

在ServletWebServerApplicationContext和ReactiveWebServerApplicationContext的refresh函数中都是调用了super.refresh();

    public void refresh() throws BeansException, IllegalStateException {
        Object var1 = this.startupShutdownMonitor;
        synchronized(this.startupShutdownMonitor) {
            this.prepareRefresh();
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
            this.prepareBeanFactory(beanFactory);

            try {
                this.postProcessBeanFactory(beanFactory);
                this.invokeBeanFactoryPostProcessors(beanFactory);
                this.registerBeanPostProcessors(beanFactory);
                this.initMessageSource();
                this.initApplicationEventMulticaster();
                this.onRefresh();
                this.registerListeners();
                this.finishBeanFactoryInitialization(beanFactory);
                this.finishRefresh();
            } catch (BeansException var9) {
                if(this.logger.isWarnEnabled()) {
                    this.logger.warn("Exception encountered during context initialization \
                    - cancelling refresh attempt: " + var9);
                }

                this.destroyBeans();
                this.cancelRefresh(var9);
                throw var9;
            } finally {
                this.resetCommonCaches();
            }

        }
    }

在这段代码中我们可以看到，其是使用了上下文中的startupShutdownMonitor属性创建一个同步代码库来执行的刷新动作。首先是实验this.prepareRefresh();准备刷新上下文：

    protected void prepareRefresh() {
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        this.active.set(true);
        if(this.logger.isInfoEnabled()) {
            this.logger.info("Refreshing " + this);
        }

        this.initPropertySources();
        this.getEnvironment().validateRequiredProperties();
        this.earlyApplicationEvents = new LinkedHashSet();
    }

接着获取了bean工厂以后，设置了一些bean工厂的环境：

    protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        beanFactory.setBeanClassLoader(this.getClassLoader());
        beanFactory.setBeanExpressionResolver(
        new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        beanFactory.addPropertyEditorRegistrar(
        new ResourceEditorRegistrar(this, this.getEnvironment()));
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
        if(beanFactory.containsBean("loadTimeWeaver")) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(
            new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        if(!beanFactory.containsLocalBean("environment")) {
            beanFactory.registerSingleton("environment", this.getEnvironment());
        }

        if(!beanFactory.containsLocalBean("systemProperties")) {
            beanFactory.registerSingleton("systemProperties",
            this.getEnvironment().getSystemProperties());
        }

        if(!beanFactory.containsLocalBean("systemEnvironment")) {
            beanFactory.registerSingleton("systemEnvironment",
            this.getEnvironment().getSystemEnvironment());
        }

    }

接下来是发送了一个bean工厂的处理信号，其中ServletWebServerApplicationContext中的实现是在bean工厂里添加了一个WebApplicationContextServletContextAwareProcessor处理器：

    protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        beanFactory.addBeanPostProcessor(
        new WebApplicationContextServletContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(ServletContextAware.class);
    }

紧接着就是调用了这处理器，并且注册到bean工厂。然后就是分别调用了initMessageSource()和initApplicationEventMulticaster()用于初始化监听器和监听管理器：

    protected void initMessageSource() {
        ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
        if(beanFactory.containsLocalBean("messageSource")) {
            this.messageSource = (MessageSource)beanFactory
            .getBean("messageSource", MessageSource.class);
            if(this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                HierarchicalMessageSource dms = (HierarchicalMessageSource)this.messageSource;
                if(dms.getParentMessageSource() == null) {
                    dms.setParentMessageSource(this.getInternalParentMessageSource());
                }
            }

            if(this.logger.isDebugEnabled()) {
                this.logger.debug("Using MessageSource [" + this.messageSource + "]");
            }
        } else {
            DelegatingMessageSource dms1 = new DelegatingMessageSource();
            dms1.setParentMessageSource(this.getInternalParentMessageSource());
            this.messageSource = dms1;
            beanFactory.registerSingleton("messageSource", this.messageSource);
            if(this.logger.isDebugEnabled()) {
                this.logger.debug("Unable to locate MessageSource with name
                \'messageSource\': using default [" + this.messageSource + "]");
            }
        }

    }

    protected void initApplicationEventMulticaster() {
        ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
        if(beanFactory.containsLocalBean("applicationEventMulticaster")) {
            this.applicationEventMulticaster = (ApplicationEventMulticaster)beanFactory
            .getBean("applicationEventMulticaster", ApplicationEventMulticaster.class);
            if(this.logger.isDebugEnabled()) {
                this.logger.debug("Using ApplicationEventMulticaster [" +
                this.applicationEventMulticaster + "]");
            }
        } else {
            this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
            beanFactory.registerSingleton("applicationEventMulticaster",
            this.applicationEventMulticaster);
            if(this.logger.isDebugEnabled()) {
                this.logger.debug("Unable to locate ApplicationEventMulticaster with name
                \'applicationEventMulticaster\':
                 using default [" + this.applicationEventMulticaster + "]");
            }
        }

    }

在initMessageSource函数中会首先判断beanFactory工厂中是否已经存在messageSource，如果不存在就会为当前的messageSource创建一个新的DelegatingMessageSource。

initApplicationEventMulticaster的初始化方式跟initMessageSource差不多，这里不再多述。

继续看run函数，接下来调用onRefresh()函数，这个函数只是发送一个刷新的事件，源码中并没有具体的实现。

接着放下看，this.registerListeners();把spring容器内的listener和beanfactory的listener都添加到广播器中：

    protected void registerListeners() {
        Iterator listenerBeanNames = this.getApplicationListeners().iterator();

        while(listenerBeanNames.hasNext()) {
            ApplicationListener earlyEventsToProcess = (ApplicationListener)listenerBeanNames.next();
            this.getApplicationEventMulticaster().addApplicationListener(earlyEventsToProcess);
        }

        String[] var6 = this.getBeanNamesForType(ApplicationListener.class, true, false);
        String[] var7 = var6;
        int var3 = var6.length;

        for(int earlyEvent = 0; earlyEvent < var3; ++earlyEvent) {
            String listenerBeanName = var7[earlyEvent];
            this.getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        Set var8 = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if(var8 != null) {
            Iterator var9 = var8.iterator();

            while(var9.hasNext()) {
                ApplicationEvent var10 = (ApplicationEvent)var9.next();
                this.getApplicationEventMulticaster().multicastEvent(var10);
            }
        }

    }

通过this.finishBeanFactoryInitialization(beanFactory);实例化BeanFactory 中已经被注册但是没被实例化的所有实例。初始化的过程中各种BeanPostProcessor就开始生效了：

    protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        if(beanFactory.containsBean("conversionService") &&
        beanFactory.isTypeMatch("conversionService", ConversionService.class)) {

            beanFactory.setConversionService((ConversionService)beanFactory
            .getBean("conversionService", ConversionService.class));
        }

        if(!beanFactory.hasEmbeddedValueResolver()) {
            beanFactory.addEmbeddedValueResolver((strVal) -> {
                return this.getEnvironment().resolvePlaceholders(strVal);
            });
        }

        String[] weaverAwareNames = beanFactory
        .getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
        String[] var3 = weaverAwareNames;
        int var4 = weaverAwareNames.length;

        for(int var5 = 0; var5 < var4; ++var5) {
            String weaverAwareName = var3[var5];
            this.getBean(weaverAwareName);
        }

        beanFactory.setTempClassLoader((ClassLoader)null);
        beanFactory.freezeConfiguration();
        beanFactory.preInstantiateSingletons();
    }

接下来调用finishRefresh()函数用于完成刷新后的一些扫尾工作，包括产生的缓存、初始化生命周期处理器LifecycleProcessor，并调用其onRefresh()方法、发布事件、调用LiveBeansView的registerApplicationContext注册context。

    protected void finishRefresh() {
        this.clearResourceCaches();
        this.initLifecycleProcessor();
        this.getLifecycleProcessor().onRefresh();
        this.publishEvent((ApplicationEvent)(new ContextRefreshedEvent(this)));
        LiveBeansView.registerApplicationContext(this);
    }

接着看run函数，在刷新完context后，调用了一个afterRefresh函数，这个函数前面已经说过了，是为了给ApplicationContext的子类留下的一个扩展点。

然后调用了listeners.started(context);，把监听器设置成了已经启动的状态。

最后调用了callRunners函数，获取所有的ApplicationRunner和CommandLineRunner然后调用他们的run方法：

	private void callRunners(ApplicationContext context, ApplicationArguments args) {
		List<Object> runners = new ArrayList<>();
		runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
		runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
		AnnotationAwareOrderComparator.sort(runners);
		for (Object runner : new LinkedHashSet<>(runners)) {
			if (runner instanceof ApplicationRunner) {
				callRunner((ApplicationRunner) runner, args);
			}
			if (runner instanceof CommandLineRunner) {
				callRunner((CommandLineRunner) runner, args);
			}
		}
	}

总结：spring boot 2.0在启动的时候，首先会调用SpringApplication的构造函数进行初始化，调用实例函数run，在run函数中，首先获取监听器，并设置成启动状态，后面准备环境prepareEnvironment，准备prepareContext上下文，刷新上下文refreshContext，最后调用callRunners来依次调用注册的Runner。