Spring IOC源码深度解析

摘要：这个读取器可以读取注解标注下的所有定义，并最终添加到的中。处理注解的配置类读取每一个配置类中定义的，加入到容器中。

IOC的核心就是代码入口就在AbstractApplictionContext

    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // 在刷新容器前进行一些准备工作，例如设置容器的激活状态，校验容器环境所必须的启动参数
            prepareRefresh();

            // 刷新内部的BeanFactory，获得一个新鲜的BeanFactory，这里面主要是读取XML文件，将其转换为BeanDefinition
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // 对BeanFactory进行进一步的完善，包括注册应用上下文感知以及监听器感知的BeanPostProcessor，
            // 先注册一些系统的环境Bean
            prepareBeanFactory(beanFactory);

            try {
                // 给子类在初始化BeanFactory重写修改变动beanFactory的权利
                postProcessBeanFactory(beanFactory);

                // 调用BeanFactoryPostProcessor，可以修改beanFactory，与上面不同的是，这里是类似插件的形式，耦合度更低
                invokeBeanFactoryPostProcessors(beanFactory);

                // 提前注册BeanPostProcessor，用于后期提供代理等功能
                registerBeanPostProcessors(beanFactory);

                // 初始化消息源，用于国际化
                initMessageSource();

                // 初始化应用事件广播器，用于广播应用上下文事件
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // 为应用事件广播器初始化监听器(ApplicationListener)
                registerListeners();

                // 实例化并注册所有非懒加载的bean
                finishBeanFactoryInitialization(beanFactory);

                // 刷新容器后的额外工作，初始化生命周期执行器，发布容器刷新完毕的应用上下文事件
                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 {
                // 清除掉不再需要的缓存，节省空间
                resetCommonCaches();
            }
        }
    }

---分析一下上面代码中的invokeBeanFactoryPostProcessors(beanFactory)源码---开始

    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        // 调用所有的BeanFactoryPostProcessors
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

        // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
        // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    }

我们知道BeanFactoryPostProcessor可以对已经生成好的BeanDefinition进行修改，也可以动态的添加来自第三方的BeanDefinition。比如我们熟知的Mybatis中的Mapper对象。如果我们使用Spring-Mybatis包中的注解@MapperScan则可以将我们定义的mapper对象加入到Spring容器中,便于我们在项目中注入到指定的地方。

@MapperScan("com.demo")
@Configuration
public class Configuration(){
}


@Service
public class Service{
@Autowired
private DemoMapper demoMapper;
}

public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {

        // 存放所有已经调用过的BeanFactoryPostProcessor，避免重复执行
        Set processedBeans = new HashSet();

        // Spring默认使用的BeanFactory是DefaultListableBeanFactory，其已经实现了BeanDefinitionRegistry接口
        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            // 用于存放普通的BeanFactoryPostProcessor
            List regularPostProcessors = new LinkedList();
            // 用于存放BeanDefinitionRegistryPostProcessor
            List registryPostProcessors =
                    new LinkedList();
           /* 执行我们自定义的beanFactoryPostProcessor，Spring提供customizeContext()方法给予我们定制化构建            
             ApplicationContext的机会，所以在这个方法中我们可以动态的添加自定义的BeanFactoryPostProcessor。
             这里将普通的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor区分开分别执行。
            */
            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryPostProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryPostProcessors.add(registryPostProcessor);
                }
                else {
                    regularPostProcessors.add(postProcessor);
                }
            }

            
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

            // 调用实现了PriorityOrdered接口的BeanFactoryPostProcessor
            List priorityOrderedPostProcessors = new ArrayList();
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            // 按照权重排序
            sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
            registryPostProcessors.addAll(priorityOrderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);

            // 调用实现了 Ordered接口的，步骤跟上面一样.
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            List orderedPostProcessors = new ArrayList();
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, orderedPostProcessors);
            registryPostProcessors.addAll(orderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);

            // 最后调用其它的BeanFactoryPostProcessor
            // 如果有BeanDefinitionRegistryPostProcessor被执行, 则有可能会产生新的BeanDefinitionRegistryPostProcessor,因此这边将reiterate赋值为true, 代表需要再循环查找一次
            boolean reiterate = true;
            while (reiterate) {
                reiterate = false;
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) {
                    if (!processedBeans.contains(ppName)) {
                        BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);
                        registryPostProcessors.add(pp);
                        processedBeans.add(ppName);
                        pp.postProcessBeanDefinitionRegistry(registry);
                        reiterate = true;
                    }
                }
            }

            invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
        }

        else {
            invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
        }

        /* 上面是通过customizeContext来动态添加BeanPostProcessor，而从这里的代码我们可以看出，只要我们写好一个
        BeanFactoryPostProcessor，使用任意方法将其加入到Spring容器中，Spring也可以解析后执行。这里足以看出Spring强大的兼容性*/
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        List priorityOrderedPostProcessors = new ArrayList();
        List orderedPostProcessorNames = new ArrayList();
        List nonOrderedPostProcessorNames = new ArrayList();
        for (String ppName : postProcessorNames) {
            if (processedBeans.contains(ppName)) {
                // 跳过已经执行过的
            }
            else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        List orderedPostProcessors = new ArrayList();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        List nonOrderedPostProcessors = new ArrayList();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

        // 清空Bean工厂的元数据缓存，因为在BeanFactoryPostProcessor中可能已经更改了BeanDefinition，所以这里需要清空
        beanFactory.clearMetadataCache();
    }

这个方法比较长，我个人觉得spring应当将其拆分成一个个小的方法，使结构更加清晰。

BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口，它提供了动态注册Bean的能力。
我们最常使用的是它的实现类ConfigurationClassPostProcessor，其带有一个Bean定义读取器。这个读取器可
以读取@Configuration、@Import、@ImportResource注解标注下的所有Bean定义，并最终添加到Spring的BeanFactory中。

public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
        PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {
***
private ConfigurationClassBeanDefinitionReader reader;
***
}

无论是在普通的Spring项目亦或是SpringBoot项目，只要我们开启了对注解配置的支持，那么系统就会自动注册ConfigurationClassPostProcessor

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
        /**
         * 获取所有的配置定义，注意：此时系统中没有任何我们自定义的@Configuration配置定义。
         * 但如果是SpringBoot项目，系统默认会将启动类SpringBootApplication加入到系统配置定义中去。
         */
        Set configCandidates = new LinkedHashSet();
        for (String beanName : registry.getBeanDefinitionNames()) {
            BeanDefinition beanDef = registry.getBeanDefinition(beanName);
            if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
                configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
            }
        }

        // 如果配置类为空，立即返回
        if (configCandidates.isEmpty()) {
            return;
        }

        // 这里初始化一些生成器
        SingletonBeanRegistry singletonRegistry = null;
        if (registry instanceof SingletonBeanRegistry) {
            singletonRegistry = (SingletonBeanRegistry) registry;
            if (!this.localBeanNameGeneratorSet && singletonRegistry.containsSingleton(CONFIGURATION_BEAN_NAME_GENERATOR)) {
                BeanNameGenerator generator = (BeanNameGenerator) singletonRegistry.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);
                this.componentScanBeanNameGenerator = generator;
                this.importBeanNameGenerator = generator;
            }
        }

        // 递归解析每一个@Configuration配置类
        ConfigurationClassParser parser = new ConfigurationClassParser(
                this.metadataReaderFactory, this.problemReporter, this.environment,
                this.resourceLoader, this.componentScanBeanNameGenerator, registry);
        for (BeanDefinitionHolder holder : configCandidates) {
            BeanDefinition bd = holder.getBeanDefinition();
            try {
                if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
                    parser.parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
                }
                else {
                    parser.parse(bd.getBeanClassName(), holder.getBeanName());
                }
            }
            catch (IOException ex) {
                throw new BeanDefinitionStoreException("Failed to load bean class: " + bd.getBeanClassName(), ex);
            }
        }
        /**
         * 校验解析出的所有@Configuration配置类，例如如果是@Configuration注解标注的full配置类，那么类不能被声明为final，否则报错。因为Spring会为
         * 每一个@Configuration配置类创建一个CGLIB代理，我们知道CGLIB是通过继承关系来实现代理的，既然用到继承，其父类肯定不能为final。
          */
        parser.validate();

        // 处理@PropertySource注解的配置类
        Stack> parsedPropertySources = parser.getPropertySources();
        if (!parsedPropertySources.isEmpty()) {
            if (!(this.environment instanceof ConfigurableEnvironment)) {
                logger.warn("Ignoring @PropertySource annotations. " +
                        "Reason: Environment must implement ConfigurableEnvironment");
            }
            else {
                MutablePropertySources envPropertySources = ((ConfigurableEnvironment)this.environment).getPropertySources();
                while (!parsedPropertySources.isEmpty()) {
                    envPropertySources.addLast(parsedPropertySources.pop());
                }
            }
        }

        /* 读取每一个@Configuration配置类中定义的bean，加入到ioc容器中。包括使用@Bean注解标注的方法，@Import导入的registry注册器，
        * @ImportResource导入的xml资源
        */
        if (this.reader == null) {
            this.reader = new ConfigurationClassBeanDefinitionReader(
                    registry, this.sourceExtractor, this.problemReporter, this.metadataReaderFactory,
                    this.resourceLoader, this.environment, this.importBeanNameGenerator);
        }
        this.reader.loadBeanDefinitions(parser.getConfigurationClasses());

        // Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes
        if (singletonRegistry != null) {
            if (!singletonRegistry.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
                singletonRegistry.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
            }
        }
    }

---分析一下上面代码中的invokeBeanFactoryPostProcessors(beanFactory)源码---结束

未完待续。。。