一、前言
- Springboot源码解析是一件大工程，逐行逐句的去研究代码，会很枯燥，也不容易坚持下去。
- 我们不追求大而全，而是试着每次去研究一个小知识点，最终聚沙成塔，这就是我们的springboot源码管中窥豹系列。
二、ApplicationContextAware
- 假设我们想使用某个bean, 如果是在@Component类下面，直接用@Autowired引用就行了
- 假设我们想在某个静态方法里面用，就不能用上面的方法了
- 你可能想用new Bean()的方式，new一个，但是这个bean里面的@Autowired引用用不了
- 如果有一个静态的全局ApplicationContext就好了，用spring的能力获取bean: ApplicationContext.getBean(clazz)
- ApplicationContextAware就是这个用处
public interface ApplicationContextAware extends Aware {
void setApplicationContext(ApplicationContext applicationContext) throws BeansException;
}
public interface Aware {
}
我们写一个实现类：
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
@Component
public class SpringContextUtil implements ApplicationContextAware {
private static ApplicationContext applicationContext;
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
SpringContextUtil.applicationContext = applicationContext;
}
private static ApplicationContext getApplicationContext() {
return applicationContext;
}
public static <T> T getBean(Class<T> clazz){
return getApplicationContext().getBean(clazz);
}
}
- 通过setApplicationContext，把applicationContext赋值到本地静态变量
- 通过ApplicationContext的getBean就可以在静态方法中使用任何bean的能力了
三、源码分析
我们进入SpringApplication的run方法：
public ConfigurableApplicationContext run(String... args) {
...
try {
...
refreshContext(context);
...
}
catch (Throwable ex) {
...
}
...
return context;
}
我们进入refreshContext(context)内部：
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);
}
destroyBeans();
cancelRefresh(ex);
throw ex;
}
finally {
resetCommonCaches();
}
}
}
这个refresh是spring的核心方法，以后会多次用到，内容太多，我们这次只关注一个方法：
- prepareBeanFactory(beanFactory);
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
...
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
...
}
}
我们先看prepareBeanFactory(beanFactory)：
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
...
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
...
}
我们看一下这个addBeanPostProcessor方法
private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
@Override
public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
// Remove from old position, if any
this.beanPostProcessors.remove(beanPostProcessor);
// Track whether it is instantiation/destruction aware
if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
this.hasInstantiationAwareBeanPostProcessors = true;
}
if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
this.hasDestructionAwareBeanPostProcessors = true;
}
// Add to end of list
this.beanPostProcessors.add(beanPostProcessor);
}
- 先remove,再add
- beanPostProcessors是一个线程安全的list: CopyOnWriteArrayList
- 我们往下看看new ApplicationContextAwareProcessor(this)，注意：this是ApplicationContext
class ApplicationContextAwareProcessor implements BeanPostProcessor {
private final ConfigurableApplicationContext applicationContext;
private final StringValueResolver embeddedValueResolver;
/**
* Create a new ApplicationContextAwareProcessor for the given context.
*/
public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
this.applicationContext = applicationContext;
this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
}
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
return bean;
}
AccessControlContext acc = null;
if (System.getSecurityManager() != null) {
acc = this.applicationContext.getBeanFactory().getAccessControlContext();
}
if (acc != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareInterfaces(bean);
return null;
}, acc);
}
else {
invokeAwareInterfaces(bean);
}
return bean;
}
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
}
- 构造方法，把applicationContext设到本地变量上
- 实现接口的方法：postProcessBeforeInitialization，回调的时候会用，主要是校验权限
- 最下面的invokeAwareInterfaces是个私有的核心回调方法，根据不同类型，有不同回调
我们看到除了ApplicationContextAware，还有其它的aware, 总共6个
- EnvironmentAware：环境变量
- EmbeddedValueResolverAware：值解析器
- ResourceLoaderAware：资源加载器
- ApplicationEventPublisherAware：事件发布器
- MessageSourceAware：信息处理器
- ApplicationContextAware：spring容器
比如我们想用全局的环境变量，就有EnvironmentAware，想用spring的事件就用ApplicationEventPublisherAware，等等
- 来源找到了，ApplicationContextAwareProcessor什么时候执行的呢？
- 这个比较麻烦，我们后面单开一节再详细的去看。
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