SpringIoc源码解析

1、先上测试代码

public static void main(String[] args){ 
//配置文件来启动一个 ApplicationContext
 ApplicationContext context = new ClassPathXmlApplicationContext("classpath:application.xml");           
 System.out.println("context 启动成功");
//从context 中取出我们的 Bean，而不是用 new HelloServiceImpl() 这种方式
 HelloService helloService = context.getBean(HelloService.class);
// 这句将输出: ok
 System.out.println(helloService.get();
}

public interface HelloService {
    String get();
}

public class HelloServiceImpl implements HelloService{
    @Override
    public String get() {
        return "ok";
    }
}

在resource目录下创建application.xml

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd" default-autowire="byName">

    <bean id="helloService" class="com.***.HelloServiceImpl"/>
</beans>

2、我看一下new ClassPathXmlApplicationContext("classpath:application.xml")干了些什么

跟踪可以发现ClassPathXmlApplicationContext继承ApplicationContext

下面沿着代码一步步看都干了些什么：

public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
        this(new String[] {configLocation}, true, null);
    }

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
            throws BeansException {
        //获取资源管理器
        super(parent);
        //设置配置文件路径，即classpath:application.xml，当然结果是个数组
        setConfigLocations(configLocations);
        //这里是我们的重点，重新创建一个AbstractApplicationContext
        if (refresh) {
            refresh();
        }
    }
//AbstractApplicationContext中实现了super(parent)
public AbstractApplicationContext() {
        this.resourcePatternResolver = getResourcePatternResolver();
    }

3、看一下refresh方法的执行过程

一些不重要的就不把代码贴出来了，只写方法注释。重要的会在后面拎出来单独详解

public void refresh() throws BeansException, IllegalStateException {
        //加锁，防止在refresh过程中，重启或销毁造成不必要的问题
        synchronized (this.startupShutdownMonitor) {
            // 准备此上下文以进行刷新，设置其启动日期和，活动标志以及执行属性源的任何初始化，校验 xml 配置文件。
            prepareRefresh();
            // 创建beanFactory，解析配置文件为一个个beanDefinition(类似map，key是beanname，value是bean属性（总有的有，beanname，是否懒加载，作用范围，依赖等等）)，然后放到beanFactory中，详细看步骤4
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            // 设置 BeanFactory 的类加载器，添加几个 BeanPostProcessor，手动注册几个特殊的 bean，详情看步骤5
            prepareBeanFactory(beanFactory);

            try {
                //允许上下文子类在初始化的时候对beanFactory进行修改
                postProcessBeanFactory(beanFactory);

                //调用所有beanFactoryPostProcessor对beanDefinite信息进行修改，详情见步骤6
                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();
            }
        }
    }

4、ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory()执行过程

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //关闭旧的 BeanFactory (如果有)，创建新的 BeanFactory，加载 Bean 定义、注册 Bean 等
        refreshBeanFactory();
        //返回刚刚创建的beanFactory
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {//是否已经存在beanFactory
            destroyBeans();//销毁所有bean
            closeBeanFactory();//关闭beanFactory
        }
        try {
            //创建DefaultListableBeanFactory，为什么用这个，可以参考beanFactory继承结构
            //ApplicationContext 继承自 BeanFactory，但是它不应该被理解为 BeanFactory 的实现类，而是说其内部持有一个实例化的 BeanFactory（DefaultListableBeanFactory）。以后所有的 BeanFactory 相关的操作其实是委托给这个实例来处理的。
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            //序列化id
            beanFactory.setSerializationId(getId());
            //设置 BeanFactory 的两个配置属性：是否允许 Bean 覆盖、是否允许循环引用
            customizeBeanFactory(beanFactory);
            //解析配置文件的封装成beandefinite，加载到beanFactory（解析过程就不多少了，想了解的同学可以看看）
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
        if (this.allowBeanDefinitionOverriding != null) {
            //设置是否允许bean被覆盖
            beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        if (this.allowCircularReferences != null) {
            //设置是否可以循环引用
            beanFactory.setAllowCircularReferences(this.allowCircularReferences);
        }
    }

了解完后，我们回到步骤3继续跟代码

5、prepareBeanFactory(beanFactory)详情

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // 设置类加载器
        // return (this.classLoader != null ? this.classLoader : ClassUtils.getDefaultClassLoader())
        //这里是当前ApplicationContext类的类加载器
        beanFactory.setBeanClassLoader(getClassLoader());
        //设置bean的表达式解析器
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        //添加注册编辑属性
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        // 添加一个beanPostProcessor，这个挺重要
        //它会检测该对象是否实现了xxxAware接口，并将相关的xxxAware实例注入给bean，如BeanNameAware等
        //关于xxxAware的作用可以参考这个http://www.what21.com/article/view/b_java_1484728658282.html
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        // 下面几行的意思就是，如果某个 bean 依赖于以下几个接口的实现类，在自动装配的时候忽略它们，
        // Spring 会通过其他方式来处理这些依赖。
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

        // 下面是处理几个特殊的bean注入相应的值
        // 
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);

        // 添加一个beanPostProcessor，在bean被实例化后，如果是ApplicationListener的子类，则加到listeners中
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

        // 如果bean是LoadTimeWeaver，则织入（在运行时织入，是和AOP相似，只是时机不一样）
        if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            // 设置一个临时的类加载器
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }

        // 手动注入一些系统环境、配置所需要的bean
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }
我们回到步骤3继续

6、invokeBeanFactoryPostProcessors(beanFactory)

//实例化并调用所有已注册的BeanFactoryPostProcessor bean
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        //getBeanFactoryPostProcessors()：获取所有的beanFactoryPostProcessor
        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()));
        }
    }

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

        // 记录已经遍历的beanFactoryPostProcessor
        Set<String> processedBeans = new HashSet<String>();
        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
            List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
                    new LinkedList<BeanDefinitionRegistryPostProcessor>();

            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                //BeanDefinitionRegistryPostProcessor的子类放入registryPostProcessors中，其他放在regularPostProcessors中
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryPostProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryPostProcessors.add(registryPostProcessor);
                }
                else {
                    regularPostProcessors.add(postProcessor);
                }
            }

            // Do not initialize FactoryBeans here: We need to leave all regular beans
            // uninitialized to let the bean factory post-processors apply to them!
            // Separate between BeanDefinitionRegistryPostProcessors that implement
            // PriorityOrdered, Ordered, and the rest.
            //获取beanFactory中所有BeanDefinitionRegistryPostProcessor
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

            // 调用实现PriorityOrdered的BeanDefinitionRegistryPostProcessors
            List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
            registryPostProcessors.addAll(priorityOrderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            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);

            // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            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;
                    }
                }
            }

            // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
            invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
        }

        else {
            // Invoke factory processors registered with the context instance.
            invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (processedBeans.contains(ppName)) {
                // skip - already processed in first phase above
            }
            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);
            }
        }

        // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        // Finally, invoke all other BeanFactoryPostProcessors.
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

        // Clear cached merged bean definitions since the post-processors might have
        // modified the original metadata, e.g. replacing placeholders in values...
        beanFactory.clearMetadataCache();
    }

未完继续