java架构之路-（spring源码篇）springIOC容器源码解析（上）

　　我们这次来叭叭一下Spring的源码，这次博客主要来说说Spring源码，先粗略的撸一遍，下篇博客选几个重点去说，由于过于复杂，我也是看了一点点，我们先来过一遍源码，然后上流程图，最后我们再回头总结一下，我们来循序渐进的叭叭一下。

我们来回顾一下上次Spring博客的内容，每次都有用到AnnotationConfigApplicationContext来加载我们的配置类，我们就从这里开始。

/**
     * Create a new AnnotationConfigApplicationContext, deriving bean definitions
     * from the given annotated classes and automatically refreshing the context.  创建新的注释configapplicationcontext，获得bean定义并自动刷新上下文。
     * @param annotatedClasses one or more annotated classes,  我们的配置类
     * e.g. {@link Configuration @Configuration} classes
     */
    public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
        this();
        register(annotatedClasses);
        refresh();
    }

　　翻译过来就是“创建新的注释configapplicationcontext，获得bean定义并自动刷新上下文”。三个方法，我们先来一个个看，优先看父类有没有构造方法。AnnotationConfigApplicationContext继承了GenericApplicationContext类，所以我们先看GenericApplicationContext类的构造方法。代码很简单

父类构造方法

/**
 * Create a new GenericApplicationContext.
 * @see #registerBeanDefinition
 * @see #refresh
 */
public GenericApplicationContext() {
　　this.beanFactory = new DefaultListableBeanFactory();
}

　　这里创建了一个新的DefaultListableBeanFactory对象，也是我们熟悉的beanFactory对象，记住是DefaultListableBeanFactory对象。我们回到AnnotationConfigApplicationContext的this方法。

this

/**
 * Create a new AnnotationConfigApplicationContext that needs to be populated
 * through {@link #register} calls and then manually {@linkplain #refresh refreshed}.
 */
public AnnotationConfigApplicationContext() {
    this.reader = new AnnotatedBeanDefinitionReader(this);//注解类型的解析器
    this.scanner = new ClassPathBeanDefinitionScanner(this);//包扫描器
}

再往下扒一层。看一下那个AnnotatedBeanDefinitionReader注解类型的解析器是怎么创建的，里面都有什么。

/**
 * Create a new {@code AnnotatedBeanDefinitionReader} for the given registry.
 * If the registry is {@link EnvironmentCapable}, e.g. is an {@code ApplicationContext},
 * the {@link Environment} will be inherited, otherwise a new
 * {@link StandardEnvironment} will be created and used.
 * @param registry the {@code BeanFactory} to load bean definitions into,
 * in the form of a {@code BeanDefinitionRegistry}
 * @see #AnnotatedBeanDefinitionReader(BeanDefinitionRegistry, Environment)
 * @see #setEnvironment(Environment)
 */
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
    this(registry, getOrCreateEnvironment(registry)); //优先设置了环境并存在缓存内
}

设置了环境，将我们的beanFactory作为参数，做了this调用，

/**
 * Create a new {@code AnnotatedBeanDefinitionReader} for the given registry and using
 * the given {@link Environment}.   用registry和Environment创建一个新的AnnnotatedBeanDefinitionReader
 * @param registry the {@code BeanFactory} to load bean definitions into,
 * in the form of a {@code BeanDefinitionRegistry}
 * @param environment the {@code Environment} to use when evaluating bean definition
 * profiles.
 * @since 3.1
 */
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
    Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    Assert.notNull(environment, "Environment must not be null");
    this.registry = registry;
    this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
    AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

前三行不用看，第四行是用来解析我们@Conditional注解的。可以自己打开瞧瞧源代码。我们直接看第五行AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry); 也是很重要的代码，我们继续叭叭。

/**
 * Register all relevant annotation post processors in the given registry.
 * @param registry the registry to operate on
 * @param source the configuration source element (already extracted)
 * that this registration was triggered from. May be {@code null}.
 * @return a Set of BeanDefinitionHolders, containing all bean definitions
 * that have actually been registered by this call
 */
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
        BeanDefinitionRegistry registry, @Nullable Object source) {

    DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
    if (beanFactory != null) {
        if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
            beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
        }
        if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
            beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
        }
    }

    Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);

    if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
    if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
    if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition();
        try {
            def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
                    AnnotationConfigUtils.class.getClassLoader()));
        }
        catch (ClassNotFoundException ex) {
            throw new IllegalStateException(
                    "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
        }
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
    }

    if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
    }

    return beanDefs;
}

　　原文的注释为在给定的注册器中处理所有有意义的后置处理器，基本就是是否包含***，如果包含就set进去。这段代码是用来初始化内部的组件的。走到这里就已经初始化的Bean定义。也就是说我们的容器已经注入了定义信息，还未实例化。

this方法的上半部分就说完了，我们再来看下半部分的new ClassPathBeanDefinitionScanner，创建一个类路径扫描器，这个代码不多，就是判断我们是否使用默认的类路径扫描器。

 /**
  * Create a new {@code ClassPathBeanDefinitionScanner} for the given bean factory and
  * using the given {@link Environment} when evaluating bean definition profile metadata.
  * @param registry the {@code BeanFactory} to load bean definitions into, in the form
  * of a {@code BeanDefinitionRegistry}
  * @param useDefaultFilters whether to include the default filters for the
  * {@link org.springframework.stereotype.Component @Component},
  * {@link org.springframework.stereotype.Repository @Repository},
  * {@link org.springframework.stereotype.Service @Service}, and
  * {@link org.springframework.stereotype.Controller @Controller} stereotype annotations
  * @param environment the Spring {@link Environment} to use when evaluating bean
  * definition profile metadata
  * @param resourceLoader the {@link ResourceLoader} to use
  * @since 4.3.6
  */
 public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
                                       Environment environment, @Nullable ResourceLoader resourceLoader) {

     Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
     this.registry = registry;

     if (useDefaultFilters) {
         registerDefaultFilters();
     }
     setEnvironment(environment);
     setResourceLoader(resourceLoader);
 }

我们来直接看一下第23行代码，是否注册一个默认的过滤器（扫描策略）。25行设置环境，26行设置资源加载器。

到这里就已经制定好了我们的扫描策略了。

有点乱啊梳理一下。

register(annotatedClasses)

this部分就说你完了，再来看看register(annotatedClasses);字面意思来看是带着我们的配置文件注册，我们来看一下代码。

/**
 * Register one or more annotated classes to be processed.
 * <p>Note that {@link #refresh()} must be called in order for the context
 * to fully process the new classes.
 * @param annotatedClasses one or more annotated classes,
 * e.g. {@link Configuration @Configuration} classes
 * @see #scan(String...)
 * @see #refresh()
 */
public void register(Class<?>... annotatedClasses) {
    Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
    this.reader.register(annotatedClasses);
}

用我们上一步的reader解析器去注册，里面是一个循环方法。最终调用doRegisterBean来真正的注册。这一步我们先来简单的叫做注册吧。

直到这里其实我们容器还是没有创建的，这些都是一些前期的准备工作。最后也是最关键的一步才是我们的容器的实例化。refresh（）方法。内容超多。

@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();

            // Check for listener beans and register them.
            registerListeners();

            // Instantiate all remaining (non-lazy-init) singletons.
            finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.
            finishRefresh();
        }

        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();
        }
    }
}

我们来逐个方法看一下都是做什么的。

prepareRefresh()创建早期程序监听器。

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()通知子类刷新Bean工厂

prepareBeanFactory(beanFactory)配置工厂上下文。

postProcessBeanFactory(beanFactory)处理Bean工厂的后置处理

invokeBeanFactoryPostProcessors实例化并调用所有注册的Bean工厂的后置处理器

registerBeanPostProcessors(beanFactory)注册Bean工厂的后置处理器

initMessageSource()初始化消息源

initApplicationEventMulticaster()初始化事件多播器

onRefresh()初始化特殊定义的Bean

registerListeners()注册事件监听器

finishBeanFactoryInitialization(beanFactory)实例化剩余非懒加载Bean

finishRefresh()事件发布

resetCommonCaches()刷新缓存

就这样我们的Bean工厂就创建完成了。看着如此简单吧。后面我们来详细看一下。内部还有超多的东西。Spring源码不建议太过于深入的学习，容易陷进去....

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