spring boot 2.0 源码分析（四）

在上一章的源码分析里，我们知道了spring boot 2.0中的环境是如何区分普通环境和web环境的，以及如何准备运行时环境和应用上下文的，今天我们继续分析一下run函数接下来又做了那些事情。先把run函数的代码贴出来：

    /**
     * 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;
    }

紧接着我们就看到了这行代码：exceptionReporters1 =
this.getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[]{ConfigurableApplicationContext.class}, new Object[]{context});
这里我们看到又出现了getSpringFactoriesInstances这个函数。

回忆一下上一次我们看到getSpringFactoriesInstances函数的时候的是在getRunListeners的时候。根据spring boot 2.0 源码分析（二）里面的内容，我们知道，这行代码其实就是加载了META-INF/spring.factories配置中的org.springframework.boot.SpringBootExceptionReporter的value。为了让大家看的更清楚，我把spring boot 2.0 里面的META-INF/spring.factories贴出来：

# 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

这个类的作用是为了在出错的时候，报告我们的错误信息，继续往下看：
this.prepareContext(context, environment, listeners, ex, printedBanner);
这行代码是把上面已经创建好的对象，传递给prepareContext来准备上下文，跳转过去看一下源码定义：

    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);
    }

先来看第一行代码：context.setEnvironment(environment);这行代码的实现是在AbstractApplicationContext中，作用是把环境绑定到上下文中：

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

再来分析一下postProcessApplicationContext(context); 先查看这个函数的源码定义：

    /**
     * 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());
            }
        }
    }

该方法对 context 设置了 ResourceLoader 和 ClassLoader，并向 bean 工厂中注册了一个beanNameGenerator 。
继续往下看：applyInitializers(context); 先把源码贴出来：

    /**
     * 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);
        }
    }

这行代码是把ApplicationContextInitializer里面的定义的资源应用到上下文，关键代码在getInitializers()函数：

    /**
     * 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);
    }

在这里我看到applyInitializers函数其实就是把META-INF/spring.factories中
org.springframework.context.ApplicationContextInitializer对应的value资源应用到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);
        }

    }

在行代码是发送一个已经准备的信号给listener，跟踪过去发现默认实现是空的。

小思考：这些空的地方也许就是以后我们可以扩展的地方。

下面是注册了springApplicationArguments和springBootBanner的单例到bean工厂。
然后调用了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函数获取了bean定义的注册表，然后调用createBeanDefinitionLoader创建出BeanDefinitionLoader，在loader做了进一步设置以后，调用loader.load()函数，把资源全部加载。
今天就写到这里了，有希望一起学习spring boot 2.0源码的同学可以关注我，跟我一起分析spring boot 2.0 源码的实现方式。