spring boot 2.0 源碼分析（四）

在上一章的源碼分析里，我們知道了spring boot 2.0中的環境是如何區分普通環境和web環境的，以及如何准備運行時環境和應用上下文的，今天我們繼續分析一下run函數接下來又做了那些事情。先把run函數的代碼貼出來：

    /**
     * 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;
    }

**緊接着我們就看到了這行代碼：exceptionReporters1 = **
this.getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[]{ConfigurableApplicationContext.class}, new Object[]{context});
這里我們看到又出現了getSpringFactoriesInstances這個函數。

回憶一下上一次我們看到getSpringFactoriesInstances函數的時候的是在getRunListeners的時候。根據spring boot 2.0 源碼分析（二）里面的內容，我們知道，這行代碼其實就是加載了META-INF/spring.factories配置中的org.springframework.boot.SpringBootExceptionReporter的value。為了讓大家看的更清楚，我把spring boot 2.0 里面的META-INF/spring.factories貼出來：

# PropertySource Loaders
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader

# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener

# Error Reporters
org.springframework.boot.SpringBootExceptionReporter=\
org.springframework.boot.diagnostics.FailureAnalyzers

# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor

# Failure Analyzers
org.springframework.boot.diagnostics.FailureAnalyzer=\
org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.BindValidationFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.UnboundConfigurationPropertyFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyNameFailureAnalyzer,\
org.springframework.boot.diagnostics.analyzer.InvalidConfigurationPropertyValueFailureAnalyzer

# FailureAnalysisReporters
org.springframework.boot.diagnostics.FailureAnalysisReporter=\
org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter

這個類的作用是為了在出錯的時候，報告我們的錯誤信息，繼續往下看：
this.prepareContext(context, environment, listeners, ex, printedBanner);
這行代碼是把上面已經創建好的對象，傳遞給prepareContext來准備上下文，跳轉過去看一下源碼定義：

	private void prepareContext(ConfigurableApplicationContext context,
			ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments, Banner printedBanner) {
		context.setEnvironment(environment);
		postProcessApplicationContext(context);
		applyInitializers(context);
		listeners.contextPrepared(context);
		if (this.logStartupInfo) {
			logStartupInfo(context.getParent() == null);
			logStartupProfileInfo(context);
		}

		// Add boot specific singleton beans
		context.getBeanFactory().registerSingleton("springApplicationArguments",
				applicationArguments);
		if (printedBanner != null) {
			context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
		}

		// Load the sources
		Set<Object> sources = getAllSources();
		Assert.notEmpty(sources, "Sources must not be empty");
		load(context, sources.toArray(new Object[0]));
		listeners.contextLoaded(context);
	}

先來看第一行代碼：context.setEnvironment(environment);這行代碼的實現是在AbstractApplicationContext中，作用是把環境綁定到上下文中：

    public void setEnvironment(ConfigurableEnvironment environment) {
        this.environment = environment;
    }

再來分析一下postProcessApplicationContext(context); 先查看這個函數的源碼定義：

	/**
	 * Apply any relevant post processing the {@link ApplicationContext}. Subclasses can
	 * apply additional processing as required.
	 * @param context the application context
	 */
	protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
		if (this.beanNameGenerator != null) {
			context.getBeanFactory().registerSingleton(
					AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,
					this.beanNameGenerator);
		}
		if (this.resourceLoader != null) {
			if (context instanceof GenericApplicationContext) {
				((GenericApplicationContext) context)
						.setResourceLoader(this.resourceLoader);
			}
			if (context instanceof DefaultResourceLoader) {
				((DefaultResourceLoader) context)
						.setClassLoader(this.resourceLoader.getClassLoader());
			}
		}
	}

該方法對 context 設置了 ResourceLoader 和 ClassLoader，並向 bean 工廠中注冊了一個beanNameGenerator 。
繼續往下看：applyInitializers(context); 先把源碼貼出來：

	/**
	 * Apply any {@link ApplicationContextInitializer}s to the context before it is
	 * refreshed.
	 * @param context the configured ApplicationContext (not refreshed yet)
	 * @see ConfigurableApplicationContext#refresh()
	 */
	@SuppressWarnings({ "rawtypes", "unchecked" })
	protected void applyInitializers(ConfigurableApplicationContext context) {
		for (ApplicationContextInitializer initializer : getInitializers()) {
			Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(
					initializer.getClass(), ApplicationContextInitializer.class);
			Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
			initializer.initialize(context);
		}
	}

這行代碼是把ApplicationContextInitializer里面的定義的資源應用到上下文，關鍵代碼在getInitializers()函數：

	/**
	 * Create a new {@link SpringApplication} instance. The application context will load
	 * beans from the specified primary sources (see {@link SpringApplication class-level}
	 * documentation for details. The instance can be customized before calling
	 * {@link #run(String...)}.
	 * @param resourceLoader the resource loader to use
	 * @param primarySources the primary bean sources
	 * @see #run(Class, String[])
	 * @see #setSources(Set)
	 */
	@SuppressWarnings({ "unchecked", "rawtypes" })
	public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
		this.resourceLoader = resourceLoader;
		Assert.notNull(primarySources, "PrimarySources must not be null");
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
		this.webApplicationType = deduceWebApplicationType();
		setInitializers((Collection) getSpringFactoriesInstances(
				ApplicationContextInitializer.class));
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
		this.mainApplicationClass = deduceMainApplicationClass();
	}
	
	/**
	 * Returns read-only ordered Set of the {@link ApplicationContextInitializer}s that
	 * will be applied to the Spring {@link ApplicationContext}.
	 * @return the initializers
	 */
	public Set<ApplicationContextInitializer<?>> getInitializers() {
		return asUnmodifiableOrderedSet(this.initializers);
	}

在這里我看到applyInitializers函數其實就是把META-INF/spring.factories中
org.springframework.context.ApplicationContextInitializer對應的value資源應用到context。
**接着往下看：listeners.contextPrepared(context); **

    public void contextPrepared(ConfigurableApplicationContext context) {
        Iterator var2 = this.listeners.iterator();

        while(var2.hasNext()) {
            SpringApplicationRunListener listener = (SpringApplicationRunListener)var2.next();
            listener.contextPrepared(context);
        }

    }

在行代碼是發送一個已經准備的信號給listener，跟蹤過去發現默認實現是空的。

小思考：這些空的地方也許就是以后我們可以擴展的地方。

下面是注冊了springApplicationArguments和springBootBanner的單例到bean工廠。
然后調用了this.load(context, sources.toArray(new Object[0]));方法：

	/**
	 * Load beans into the application context.
	 * @param context the context to load beans into
	 * @param sources the sources to load
	 */
	protected void load(ApplicationContext context, Object[] sources) {
		if (logger.isDebugEnabled()) {
			logger.debug(
					"Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
		}
		BeanDefinitionLoader loader = createBeanDefinitionLoader(
				getBeanDefinitionRegistry(context), sources);
		if (this.beanNameGenerator != null) {
			loader.setBeanNameGenerator(this.beanNameGenerator);
		}
		if (this.resourceLoader != null) {
			loader.setResourceLoader(this.resourceLoader);
		}
		if (this.environment != null) {
			loader.setEnvironment(this.environment);
		}
		loader.load();
	}

首先getBeanDefinitionRegistry函數獲取了bean定義的注冊表，然后調用createBeanDefinitionLoader創建出BeanDefinitionLoader，在loader做了進一步設置以后，調用loader.load()函數，把資源全部加載。
今天就寫到這里了，有希望一起學習spring boot 2.0源碼的同學可以關注我，跟我一起分析spring boot 2.0 源碼的實現方式。