spring 源码-context(一)

1 spring-context 模块概要

该模块主要实现在spring-beans 模块的扩展，主要对aop支持及el表达式的实现

分析示例

  public static void main(String[] args){
    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring-aop.xml");

    TestBean testBean = (TestBean) context.getBean("testBean");
    testBean.test();
    System.out.println(testBean);
  }

xml配置

<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:aop="http://www.springframework.org/schema/aop"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
            http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop-3.2.xsd">

  <aop:aspectj-autoproxy proxy-target-class="false"/>
  <bean id="testBean" class="com.xie.java.aop.TestBean"/>
  <bean id="aspectJTest" class="com.xie.java.aop.AspectJTest"/>
beans>

从ClassPathXmlApplicationContext 入手，先看下该类的继承结构

2 applicationcontext 初始化

从上面来看该类继承还是非常复杂的，不管怎么样，先从调用的地方入手

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

    public ClassPathXmlApplicationContext(String... configLocations) throws BeansException {
        this(configLocations, true, null);
    }

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
            throws BeansException {

        super(parent);
        //处理配置资源初始化
        setConfigLocations(configLocations);
        if (refresh) {
            //这是真正的核心入口
            refresh();
        }
    }

上面都是一些非常简单的代码，无需多解释,接下来主要是看AbstractApplicationContext.refresh方法,context 绝大部分功能由AbstractApplicationContext去实现,下面是主线实现代码，包括利用beanfactory加载beandefinitions 及实例化这些beans 以及aop的实现

    @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            //刷新前一些准备
            prepareRefresh();
            //获得beafactory，并加载beandefinition
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            //准备一下beanfactory的信息
            prepareBeanFactory(beanFactory);
            try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                //调用beanfactoryPostProcessors
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                //注册bean processors 用于拦截bean的创建
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                //初始化容器消息源
                initMessageSource();

                // Initialize event multicaster for this context.
                //初始化事件广播者
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                //初始化子容器其它特定beans 
                onRefresh();

                // Check for listener beans and register them.
                //注册监听者
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                //实例化所有拥有非懒加载的单例
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                //最后一步，发布对应的事件
                finishRefresh();
            }
    //省略一些代码
        }
    }

    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

    @Override
    protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
            //创建beafactory
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
            //加载beandefinitions 
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }
    @Override
    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // Create a new XmlBeanDefinitionReader for the given BeanFactory.
        //创建xml beandefinition reader
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

        // Configure the bean definition reader with this context's
        // resource loading environment.
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

        // Allow a subclass to provide custom initialization of the reader,
        // then proceed with actually loading the bean definitions.
        initBeanDefinitionReader(beanDefinitionReader);
        //通过xml reader 读取xml配置文件 
        loadBeanDefinitions(beanDefinitionReader);
    }
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
        //获得所有配置资源
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            //正式通过xmlreader解释xml 配置，并把解释到的beandedinition
            //注册到beanfactory里，接下来就是beans模块已讲过的了
            reader.loadBeanDefinitions(configLocations);
        }
    }

3 预实例化beanfactory里单例对象

接下要分析如何把上面得到的beandefinitions 进行实例化

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        // Initialize conversion service for this context.
        if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
                beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
    //省略一大波代码
    // Instantiate all remaining (non-lazy-init) singletons.
    //预实例化单例，
        beanFactory.preInstantiateSingletons();
}

获取beanfactory里所有beanNames进行实例化

@Override
public void preInstantiateSingletons() throws BeansException {
        //获得所有beanNames 
        List beanNames = new ArrayList(this.beanDefinitionNames);

        //逐个遍历，实例化预加载单例对象
        for (String beanName : beanNames) {
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                //判断要创建的实例是否为FactoryBean
                if (isFactoryBean(beanName)) {
                    final FactoryBean factory = (FactoryBean) getBean(FACTORY_BEAN_PREFIX + beanName);
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged(new PrivilegedAction() {
                            @Override
                            public Boolean run() {
                                return ((SmartFactoryBean) factory).isEagerInit();
                            }
                        }, getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
                else {
                    //开始他建实例，这块是beans模块内容，不再重述了
                    getBean(beanName);
                }
            }
        }
        //这里省略一些代码
}