一、进入正题
Aware本义就是"自动的",顾名思义spring给我们自动做了些事情。spring有很多以Aware结尾的类,有EnvironmentAware、ApplicationContextAware、MessageSourceAware等。这里我主要讲一下ApplicationContextAware。
二、使用
@Service("gatewayService")
public class GatewayServiceImpl implements IGatewayService,ApplicationContextAware {
private Logger logger= LoggerFactory.getLogger(getClass());
Map<ServiceBeanEnum,IGatewayBo> chargeHandlerMap=new HashMap<ServiceBeanEnum,IGatewayBo>();
private ApplicationContext applicationContext;
@Override
public void setApplicationContext(ApplicationContext applicationContext)
throws BeansException {
this.applicationContext=applicationContext;
}
}
在我们需要使用ApplicationContext的服务中实现ApplicationContextAware接口,系统启动时就可以自动给我们的服务注入applicationContext对象,我们就可以获取到ApplicationContext里的所有信息了。
三、原理分析
我们都知道spring的入口方法就在AbstractApplicationContext的refresh()方法.我们先去看看refresh().prepareBeanFactory()方法。
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// 添加ApplicationContextAware的处理器
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
...
}
也就是说,spring在启动的时候给我们添加了ApplicationContextAwareProcessor这样一个processor。进去看看它的实现:
@Override
public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
AccessControlContext acc = null;
if (System.getSecurityManager() != null &&
(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
acc = this.applicationContext.getBeanFactory().getAccessControlContext();
}
if (acc != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
//核心方法,调用aware接口方法
invokeAwareInterfaces(bean);
return null;
}
}, acc);
}
else {
invokeAwareInterfaces(bean);
}
return bean;
}
//实现
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof Aware) {
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);
}
//针对实现了ApplicationContextAware的接口,spring都将调用其setApplicationContext,将applicationContext注入到当前bean对象。
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
}
那ApplicationContextAwareProcessor又是什么时候调用的呢？我们接着往下看,原来refresh()方法中还有个beanFactory.preInstantiateSingletons()方法,里面有这样一段代码:
拿到所有的beanNames,然后依次判断是否需要加载,如果是,则调用getBean(beanName)方法实例化出来。
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
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<Boolean>() {
@Override
public Boolean run() {
return ((SmartFactoryBean<?>) factory).isEagerInit();
}
}, getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
else {
getBean(beanName);
}
}
}
依次查看getBean() ->doGetBean()->createBean()->doCreateBean()方法:
// Initialize the bean instance.
Object exposedObject = bean;
try {
populateBean(beanName, mbd, instanceWrapper);
if (exposedObject != null) {
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
}
catch (Throwable ex) {
if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
查看一下initializeBean方法:
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
invokeAwareMethods(beanName, bean);
return null;
}
}, getAccessControlContext());
}
else {
//调用setBeanName() 、setBeanClassLoaderAware、setBeanFactoryAware方法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//调用afterPropertiesSet()方法
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
//这里才是ApplicationContextProcessor的postProcessAfterInitialization()执行入口:
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
原来AbstractAutowireCapableBeanFactory中的inititalBean()方法就是BeanPostProcessor的调用处。但是像BeanNameAware、BeanFactoryAware不同,是通过initialBean()中的invokeAwareMethods直接调用实现的。
