之前简略记录了下springBean的生命周期，最近打开来看了下，发现自己脱漏了很多细节，很多点都连接不上
明天从新翻看《spring揭秘》，查资料，补了许多细节。心愿可能让本人和大家更容易看懂吧
Bean的生命周期的齐全实现须要两个阶段
- 容器的启动
- bean的实例化过程（涵盖了bean生命周期的大部分）
容器启动阶段
- 重点是收集到元信息配置信息，即创立bean须要的信息（beanDefinition）
通过BeanDefinitionReader,读取到beanDefinition信息，再通过beanDefinitionRegistry,将BeanDefinition注册到其外面
// 这是 PropertiesBeanDefinitionReader 把从properties文件读取到的配置信息，
// 通过 BeanDefinitionRegistry 注册 BeanDefinition的过程
AbstractBeanDefinition bd = BeanDefinitionReaderUtils.createBeanDefinition(
parent, className, getBeanClassLoader());
bd.setScope(scope); // 作用域 默认singleton
bd.setAbstract(isAbstract); // 是否是形象 默认false 如果是形象的，容器不会实例化bean，而是将beanDefinition信息作为其子类应用
bd.setLazyInit(lazyInit); // 懒加载 默认false 如果是false,容器一启动就会加载bean
bd.setConstructorArgumentValues(cas); // 结构参数
bd.setPropertyValues(pvs); // 属性信息
getRegistry().registerBeanDefinition(beanName, bd); // 注册BeandefinitionBeanDefinitionReader 有多种,包含:
- PropertiesBeanDefinitionReader 读取Properties配置文件
- GroovyBeanDefinitionReader 读取Groovy配置文件
- XmlBeanDefinitionReader 读取Xml配置文件
bean实例化前 对beanDefinition做出自定义批改
BeanFactoryPostProcessor实例化bean之前，能够容许批改beanDefinition信息，上面是spring默认实现的BeanFactoryPostProcessor类：
PropertyPlaceholderConfigurer容许咱们在XML配置文件中应用占位符（PlaceHolder），并将这些占位符所代表的资源独自配置到简略的properties文件中来加载PropertyOverrideConfigurer笼罩对象的属性值- 咱们能够本人实现
BeanFactoryPostProcessor依赖注入beanFactory，批改beanDefinition信息
bean实例化阶段
doCreateBean源码办法（上面仅对beanFactory容器做解析，applicationContext容器其实大同小异）
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
// 实例化bean
Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {
mbd.resolvedTargetType = beanType;
}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// Initialize the bean instance.
Object exposedObject = bean;
try {
// 填充bean对象属性
populateBean(beanName, mbd, instanceWrapper);
// 初始化bean
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);
}
}
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {
// 查看是否实现DisposableBean接口，有的话注册销毁回调办法
registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
- 首先第一步，调用
createBeanInstance办法，利用反射调用类的构造方法，实例化bean，返回beanWrapper对象,再调用getWrappedInstance办法失去实例化的bean，beanWrapper对象具备获取对象属性的性能，所以能够调用populateBean用来实现属性填充。
-
开始实例化bean之前，会查看bean有没有实现过
Aware接口，如果有则实现。// AbstractAutowireCapableBeanFactory类中的 initializeBean办法 private void invokeAwareMethods(String beanName, Object bean) { if (bean instanceof Aware) { // 如果Spring容器检测到以后对象实例实现了该接口，会将该对象实例的bean定义对应的beanName设置到以后对象实例。 if (bean instanceof BeanNameAware) { ((BeanNameAware) bean).setBeanName(beanName); } // 如果容器检测到以后对象实例实现了该接口，会将对应加载以后bean的Classloader注入以后对象实例。 // 默认会应用加载org.springframework.util.ClassUtils类的Classloader if (bean instanceof BeanClassLoaderAware) { ClassLoader bcl = getBeanClassLoader(); if (bcl != null) { ((BeanClassLoaderAware) bean).setBeanClassLoader(bcl); } } if (bean instanceof BeanFactoryAware) { ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this); } // 以上几个Aware接口只是针对BeanFactory类型的容器而言 } }
对于ApplicationContext类型容器，会额定实现几个Aware接口
- BeanPostProcessor阶段
BeanPostProcessor的概念容易与BeanFactoryPostProcessor的概念混同。
但只有记住BeanPostProcessor是存在于对象实例化阶段，而BeanFactoryPostProcessor则是存在于容器启动阶段，这两个概念就比拟容易辨别了。
BeanPostProcessor 有两个须要子类实现的办法
public interface BeanPostProcessor {
/**
* 调用bean的init办法之前做的前置解决
*/
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
/**
* 调用bean的init办法之后做的前置解决
*/
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}在initializeBean办法内能够看到BeanPostProcessor的调用程序
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// 调用实现了Aware接口的对象办法
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
// BeanPostProcessor前置解决
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
// 调用bean的init办法
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
// BeanPostProcessor后置解决
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}留神：
applcationContext容器中实现BeanPostProcessor接口的postProcessBeforeInitialization中，会对实现了Aware接口的bean进行invoke调用。
这里和BeanFactory有些不同，BeanFactory是在BeanPostProcessor之前实现的
- InitializingBean和init-method
这两个办法都是在invokeInitMethods办法里调用，InitializingBean接口须要实现afterPropertiesSet 办法容许bean实例在设置完所有bean属性后执行其整体配置验证和最终初始化。init-method, 对于用户来说能够自定义办法的名称，也能够对立设置所有对象的initMethod比拟灵便，防止批改代码，耦合性低。
- DisposableBean与destroy-method
DisposableBean接口，子类须要实现destroy办法，来销毁对象,只实用于单例对象，不是单例的话，须要交给调用者本人销毁。destroy-method注册销毁函数，作用和destroy办法同理
总结
本文次要讲了bean在BeanFacotry容器的生命周期，applicationContext容器略微提了几点不同，applicationContext容器减少更多的个性，像事件公布监听，国际化信息反对等。
bean的生命周期次要波及到容器的加载和bean的实例化。
容器的加载：
- 加载资源文件到beanDefinition（元信息）
- 调用实现了BeanFactoryPostProcessor接口的办法，能够对beanDefinition进行批改。
bean的实例化：
- 利用反射+beanDefinition元信息实例化失去对象
- populateBean办法填充属性
- 测验对象是否实现过Aware接口，有则调用其实现
- 如果对象有实现BeanPostProcessor接口，须要先实现前置办法
- 调用InitializingBean和init-method办法 如果有实现或标记的话
- 再调用BeanPostProcessor接口的后置办法
- 最初查看对象是否实现 DisposableBean与destroy-method 来销毁bean（DisposableBean接口只针对单例bean）
材料：
《spring揭秘》王福强
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