spring IOC源码解读

本文从直接调用的ClassPathXmlApplicationContext开始说起，看看spring是怎么实现IOC/DI

1.spring应用代码

其中singer.xml是自定义的

DIMp3类是自定义的。

public static void main(String[] args) {
//spring通过应用上下文装载bean的定义并组装
//使用spring实现的ClassPathXmlApplicationContext加载配置文件
@SuppressWarnings("resource")
ApplicationContext context = new ClassPathXmlApplicationContext("singer.xml");

//从应用上下文中获取bean
DIMp3 mp3 = (DIMp3) context.getBean("mp3");

mp3.play();
}

2.ClassPathXmlApplicationContext：获取容器

ClassPathXmlApplicationContext("singer.xml"); 实际调用的是

/**

* 使用configLocations指定配置文件去构造一个spring容器

* refresh是否刷新容器,默认true（具体的刷新后面讲解）

* parent: 当前容器父级容器

*/

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}

2.1 super(parent)：给定parent创建父级容器

实际调用的是

public AbstractApplicationContext(ApplicationContext parent) {
this.resourcePatternResolver = getResourcePatternResolver();//返回一个PathMatchingResourcePatternResolver对象
this.parent = parent;
if (parent != null) {
Environment parentEnvironment = parent.getEnvironment();
if (parentEnvironment instanceof ConfigurableEnvironment) {
getEnvironment().merge((ConfigurableEnvironment) parentEnvironment);
}
}//将父级容器运行时环境合并到当前容器运行时环境。
}

2.2 setConfigLocations(configLocations)：将传入的配置文件转换为容器的配置文件。

这步比较简单，只是一个简单的设值操作。

public void setConfigLocations(String[] locations) {
if (locations != null) {
Assert.noNullElements(locations, "Config locations must not be null");
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}

2.3 refresh():这一步是真正的创建容器加载bean

public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {

//这步无关紧要，就是设置一下开始刷新时间，开始记录日志，检查是否运行时环境变量是完整的
// Prepare this context for refreshing.
prepareRefresh();


// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

1.beanFactory是否存在，存在就销毁：destroyBeans();

2.根据父级beanFactory创建一个新的beanFactory：createBeanFactory();

3.定制当前的beanFactory（主要是设置对注解的支持）：customizeBeanFactory(beanFactory);

4.加载XmlBeanDefinitionReader：loadBeanDefinitions(beanFactory);


// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);

1.为beanFactory加载一个ContextClassLoader:beanFactory.setBeanClassLoader(getClassLoader());

2.加载一个BeanExpressionResolver去解析spring的el表达式例如#{}:beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver());

3.加载一个资源加载器ResourceLoader加载classpath以及一些file资源，加载一个PropertyResolver，去获取一些属性文件信 息:beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

4.加载一个BeanPostProcessor，这个处理器提供两个回调方法给spring创建bean的过程中回调。书面上交spring扩展 点：beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

5.最后是注册一些环境变量。

try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);

在ApplicationContext初始化后，修改context的 beanFactory

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

在单例应用bean之前实例化所有的 BeanFactoryPostProcessor并调用


// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);

在实例化应用bean之前实例化所有的 BeanFactoryPostProcessor并调用


// Initialize message source for this context.
initMessageSource();

使用父级messageSource初始化本context国际化组件，如果父级没有，创建一个新的 beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);


// Initialize event multicaster for this context.
initApplicationEventMulticaster();

使用实例化一个在context自定义的时间广播器，如果没有自定义的用默认的SimpleApplicationEventMulticaster


// 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) {
// Destroy already created singletons to avoid dangling resources.
destroyBeans();


// Reset 'active' flag.
cancelRefresh(ex);


// Propagate exception to caller.
throw ex;
}
}
}

3.IOC相关类说明

至此，bean已经实例化完毕。更多细节参考：

http://www.iteye.com/topic/1122859