DefaultSingletonBeanRegistry
这是 DefaultSingletonBeanRegistry 类的体系结构,由一个类一个责任的原则：
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AliasRegistry : 提供别名注册的接口
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SimpleAliasRegistry : 它简单地实现了AliasRegistry接口。
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SingletonBeanRegistry : 提供单例bean注册的接口
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DefaultSingletonBeanRegistry :它继承SimpleAliasRegistry类和实现了SingletonBeanRegistry接口，因此这个类可以有别名注册的功能和单例bean注册的功能，并且他还支持注册DisposableBean实例;它依赖ObjectFactory接口和DisposableBean接口(关闭注册表时调用到了destroy方法)。
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ObjectFactory : 这个接口通常用于封装一个通用的工厂，它只有一个方法getObject() ,它调用getObject()方法返回一个新的实例，一些在每次调用的目标对象（原型）.
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DisposableBean : 接口实现为beans要破坏释放资源。它也只有一个方法destroy(),由一个破坏一个singleton的BeanFactory调用。
/**
* 共享bean实例的通用注册表，实现了SingletonBeanRegistry. 允许注册表中注册的单例应该被所有调用者共享，通过bean名称获得。
*
* 还支持登记的DisposableBean实例，（这可能会或不能正确的注册单例），关闭注册表时destroyed.
* 可以注册bean之间的依赖关系，执行适当的关闭顺序。
*
*
* 这个类主要用作基类的BeanFactory实现， 提供基本的管理
* singleton bean 实例功能。
*
*/
public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
SingletonBeanRegistry {
// null 单例对象的内部标记：用作并发 Map(不支持null值)的标记值
protected static final Object NULL_OBJECT = new Object();
// 日志用来记录子类
protected final Log logger = LogFactory.getLog(getClass());
// singleton 对象的缓存：bean name --> bean instance
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>();
// singleton 的工厂对象的缓存：bean name --> ObjectFactory
private final Map<String, ObjectFactory> singletonFactories = new HashMap<String, ObjectFactory>();
// singletonFactory 制造出来的 singleton 的缓存：bean name --> bean instance
private final Map<String, Object> earlySingletonObjects = new HashMap<String, Object>();
//以上三个缓存是这个类存放单例 bean 的主要 Map
// 就是单例注册表
private final Set<String> registeredSingletons = new LinkedHashSet<String>(16);
// 目前正在创建中的单例 bean 的名称的集合
private final Set<String> singletonsCurrentlyInCreation = Collections.synchronizedSet(new HashSet<String>());
// 当前在创建检查中排除的 bean 的名称
private final Set<String> inCreationCheckExclusions =
Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>(16));
// 存放异常出现的相关的原因的集合
private Set<Exception> suppressedExceptions;
// 标志，指示我们目前是否在销毁单例中
private boolean singletonsCurrentlyInDestruction = false;
// 存放一次性bean的缓存
private final Map<String, Object> disposableBeans = new LinkedHashMap<String, Object>();
// 外部 bean 与其所有内部 bean 集合：外部 bean name --> 外部 bean 所包含的内部 bean 集合
private final Map<String, Set<String>> containedBeanMap = new ConcurrentHashMap<String, Set<String>>();
// 依赖这个 bean 的所有 bean 集合(依赖我的)：bean name --> 依赖这个 bean 的所有 bean 集合
private final Map<String, Set<String>> dependentBeanMap = new ConcurrentHashMap<String, Set<String>>();
// 这个 bean 依赖的所有 bean 集合(我依赖的) ：bean name --> bean 依赖的所有 bean 集合
private final Map<String, Set<String>> dependenciesForBeanMap = new ConcurrentHashMap<String, Set<String>>();
// 以上四个 map 集合都和 bean 的销毁有关
// SingletonBeanRegistry 接口的 registerSingleton 方法的实现
public void registerSingleton(String beanName, Object singletonObject)
throws IllegalStateException {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
Object oldObject = this.singletonObjects.get(beanName);
//如果 singletonObjects 缓存找到有指定名称为 beanName 的对象，则表示该了bean 已经注册
if (oldObject != null) {
throw new IllegalStateException("Could not register object ["
+ singletonObject + "] under bean name '" + beanName
+ "': there is already object [" + oldObject
+ "] bound");
}
//若该名称没被占用，真正的注册操作在这里实现
addSingleton(beanName, singletonObject);
}
}
protected void addSingleton(String beanName, Object singletonObject) {
synchronized (this.singletonObjects) {
// 因为singletonObjects类型是 ConcurrentHashMap，并发Map不支持空值作为标志值，所以用NULL_OBJECT来代替
this.singletonObjects.put(beanName,
(singletonObject != null ? singletonObject : NULL_OBJECT));
// singletonFactories、earlySingletonObjects 解决创建 singletonObject 的过程中的循环依赖用的
// bean 创建完成后就没用的，需要销毁
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
// beanName放进单例注册表中
this.registeredSingletons.add(beanName);
}
}
// 添加名称为 beanName 的 singletonFactory 对象
protected void addSingletonFactory(String beanName,
ObjectFactory singletonFactory) {
Assert.notNull(singletonFactory, "Singleton factory must not be null");
synchronized (this.singletonObjects) {
// 同理，bean 如果已经创建完成，就没有必要进行这步操作了
if (!this.singletonObjects.containsKey(beanName)) {
this.singletonFactories.put(beanName, singletonFactory);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
}
// SingletonBeanRegistry 接口的 getSingleton 方法的实现
public Object getSingleton(String beanName) {
return getSingleton(beanName, true);
}
/**
* 获取 bean 的单例
* @param beanName
* @param allowEarlyReference 是否允许循环引用
*/
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
// singletonObject = nul 说明 bean 还未创建或正在创建
// 如果 isSingletonCurrentlyInCreation(beanName) = true，说明出现了循环引用
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
// 显然 earlySingletonObjects、singletonFactories 是不能共存的
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
/**
* 真正的根据 ObjectFactory 创建 singletonObject 对象了
* @param beanName
* @param singletonFactory 创建 singletonObject 对象的工厂对象
*/
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
//1. 如果 singletonObject 还没有被创建，那就开始创建吧
if (singletonObject == null) {
//2. 如果 beanName 正在被销毁，那还创建个啥，直接抛出异常就好
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while the singletons of this factory are in destruction " +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {
logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
}
//3. 单例对象创建前的回调，一个重要的工作就是将该 bean 打上正在创建的标记
beforeSingletonCreation(beanName);
// beanName 创建成功与否的一个标记
boolean newSingleton = false;
// 判断存储异常相关原因的集合是否已存在，不存在就创建一个
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<Exception>();
}
try {
//4. 好了，创建 singletonObject
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
// 没看明白，以后补充，但逻辑还是清楚的，反正就是获取 singletonObject
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
throw ex;
}
}
catch (BeanCreationException ex) {
// 记录异常，没有什么好说的
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
//5. 单例对象创建后的回调，一个重要的工作就是将该 bean 正在创建的标记销毁
afterSingletonCreation(beanName);
}
//6. beanName 创建成功，注册创建后的单例
if (newSingleton) {
addSingleton(beanName, singletonObject);
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}
// 注册 singeton bean 实例创建过程中的异常
protected void onSuppressedException(Exception ex) {
synchronized (this.singletonObjects) {
if (this.suppressedExceptions != null) {
this.suppressedExceptions.add(ex);
}
}
}
// 销毁 beanName
protected void removeSingleton(String beanName) {
synchronized (this.singletonObjects) {
this.singletonObjects.remove(beanName);
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.remove(beanName);
}
}
// singletonBeanRegistry 接口的 containsSingleton 方法实现
public boolean containsSingleton(String beanName) {
return (this.singletonObjects.containsKey(beanName));
}
// singletonBeanRegistry 接口的 getSingletonNames 方法实现
public String[] getSingletonNames() {
// 对 singletonObjects 加锁，可能是为了防止 registeredSingletons 和 singletonObjects 出现不一致的问题
synchronized (this.singletonObjects) {
return StringUtils.toStringArray(this.registeredSingletons);
}
}
// singletonBeanRegistry 接口的 getSingletonCount 方法实现
public int getSingletonCount() {
synchronized (this.singletonObjects) {
return this.registeredSingletons.size();
}
}
// 将正在创建的 beanName 从 inCreationCheckExclusions 集合删除，已创建完成的加入 inCreationCheckExclusions
public void setCurrentlyInCreation(String beanName, boolean inCreation) {
Assert.notNull(beanName, "Bean name must not be null");
if (!inCreation) {
this.inCreationCheckExclusions.add(beanName);
}
else {
this.inCreationCheckExclusions.remove(beanName);
}
}
public boolean isCurrentlyInCreation(String beanName) {
Assert.notNull(beanName, "Bean name must not be null");
return (!this.inCreationCheckExclusions.contains(beanName) && isActuallyInCreation(beanName));
}
protected boolean isActuallyInCreation(String beanName) {
return isSingletonCurrentlyInCreation(beanName);
}
// 返回 beanName 是否正在创建，即出现了循环引用
public boolean isSingletonCurrentlyInCreation(String beanName) {
return this.singletonsCurrentlyInCreation.contains(beanName);
}
// 单例对象创建前的回调
// 创建前 singletonsCurrentlyInCreation 注册该 beanName，如果已经添加则会抛出异常
protected void beforeSingletonCreation(String beanName) {
if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.add(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
}
// 单例对象创建后的回调
// 创建后 singletonsCurrentlyInCreation 移除该 beanName，如果该 beanName 已经创建完成则会抛出异常
protected void afterSingletonCreation(String beanName) {
if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.remove(beanName)) {
throw new IllegalStateException("Singleton '" + beanName + "' isn't currently in creation");
}
}
// 一次性 bean 注册，存放在 disponsableBeans 集合中
public void registerDisposableBean(String beanName, DisposableBean bean) {
synchronized (this.disposableBeans) {
this.disposableBeans.put(beanName, bean);
}
}
/**
* 注册两个 bean 之间的控制关系
* @param containedBeanName the name of the contained (inner) bean
* @param containingBeanName the name of the containing (outer) bean
*/
public void registerContainedBean(String containedBeanName, String containingBeanName) {
// 先做一个简单的判断，避免使用 synchronized 关键字
Set<String> containedBeans = this.containedBeanMap.get(containingBeanName);
if (containedBeans != null && containedBeans.contains(containedBeanName)) {
return;
}
synchronized (this.containedBeanMap) {
containedBeans = this.containedBeanMap.get(containingBeanName);
if (containedBeans == null) {
containedBeans = new LinkedHashSet<String>(8);
this.containedBeanMap.put(containingBeanName, containedBeans);
}
containedBeans.add(containedBeanName);
}
// 紧接着调用注册内部 bean 和外部 bean 的依赖关系的方法
registerDependentBean(containedBeanName, containingBeanName);
}
/**
* 注册给定bean的一个依赖bean，给定的bean销毁之前被销毁。
*
*/
public void registerDependentBean(String beanName, String dependentBeanName) {
// 调用 SimpleAliasRegistry 的 canonicalName 方法，这方法是将参数 beanName 当做别名寻找到注册名，并依此递归
String canonicalName = canonicalName(beanName);
Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
if (dependentBeans != null && dependentBeans.contains(dependentBeanName)) {
return;
}
// 注册依赖 beanName 的集合，毫无疑问 containingBeanName 依赖 containedBeanName
// 换句话说，依赖 containedBeanName 的集合中包括 containingBeanName
synchronized (this.dependentBeanMap) {
dependentBeans = this.dependentBeanMap.get(canonicalName);
if (dependentBeans == null) {
dependentBeans = new LinkedHashSet<String>(8);
this.dependentBeanMap.put(canonicalName, dependentBeans);
}
dependentBeans.add(dependentBeanName);
}
// 注册 dependentBeanName 所依赖的集合
synchronized (this.dependenciesForBeanMap) {
Set<String> dependenciesForBean = this.dependenciesForBeanMap.get(dependentBeanName);
if (dependenciesForBean == null) {
dependenciesForBean = new LinkedHashSet<String>(8);
this.dependenciesForBeanMap.put(dependentBeanName, dependenciesForBean);
}
dependenciesForBean.add(canonicalName);
}
}
protected boolean isDependent(String beanName, String dependentBeanName) {
return isDependent(beanName, dependentBeanName, null);
}
private boolean isDependent(String beanName, String dependentBeanName, Set<String> alreadySeen) {
String canonicalName = canonicalName(beanName);
if (alreadySeen != null && alreadySeen.contains(beanName)) {
return false;
}
Set<String> dependentBeans = this.dependentBeanMap.get(canonicalName);
if (dependentBeans == null) {
return false;
}
if (dependentBeans.contains(dependentBeanName)) {
return true;
}
for (String transitiveDependency : dependentBeans) {
if (alreadySeen == null) {
alreadySeen = new HashSet<String>();
}
alreadySeen.add(beanName);
if (isDependent(transitiveDependency, dependentBeanName, alreadySeen)) {
return true;
}
}
return false;
}
// 确定是否还存在名为 beanName 的被依赖关系
protected boolean hasDependentBean(String beanName) {
return this.dependentBeanMap.containsKey(beanName);
}
// 返回依赖于指定的bean的所有bean的名称，如果有的话。(依赖我的)
public String[] getDependentBeans(String beanName) {
Set<String> dependentBeans = this.dependentBeanMap.get(beanName);
if (dependentBeans == null) {
return new String[0];
}
return StringUtils.toStringArray(dependentBeans);
}
// 返回指定的 bean 依赖于所有的 bean 的名称，如果有的话。(我依赖的)
public String[] getDependenciesForBean(String beanName) {
Set<String> dependenciesForBean = this.dependenciesForBeanMap.get(beanName);
if (dependenciesForBean == null) {
return new String[0];
}
return dependenciesForBean.toArray(new String[dependenciesForBean.size()]);
}
// 销毁所有单例
public void destroySingletons() {
if (logger.isDebugEnabled()) {
logger.debug("Destroying singletons in " + this);
}
// 单例销毁标志开始
synchronized (this.singletonObjects) {
this.singletonsCurrentlyInDestruction = true;
}
// 销毁 disponsableBeans 缓存中所有单例 bean
String[] disposableBeanNames;
synchronized (this.disposableBeans) {
disposableBeanNames = StringUtils.toStringArray(this.disposableBeans.keySet());
}
for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
destroySingleton(disposableBeanNames[i]);
}
// 销毁内部所有的集合
this.containedBeanMap.clear();
this.dependentBeanMap.clear();
this.dependenciesForBeanMap.clear();
synchronized (this.singletonObjects) {
this.singletonObjects.clear();
this.singletonFactories.clear();
this.earlySingletonObjects.clear();
this.registeredSingletons.clear();
// 单例目前正在销毁标志为结束
this.singletonsCurrentlyInDestruction = false;
}
}
public void destroySingleton(String beanName) {
// Remove a registered singleton of the given name, if any.
removeSingleton(beanName);
// Destroy the corresponding DisposableBean instance.
DisposableBean disposableBean;
synchronized (this.disposableBeans) {
disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
}
destroyBean(beanName, disposableBean);
}
// 真正的销毁 beanName
// 毫无疑问，销毁该 beanName 之前要将依赖这个 beanName 的所有 bean 都销毁
protected void destroyBean(String beanName, DisposableBean bean) {
//1. 先销毁依赖这个 beanName 的所有实例
Set<String> dependencies = this.dependentBeanMap.remove(beanName);
if (dependencies != null) {
if (logger.isDebugEnabled()) {
logger.debug("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);
}
for (String dependentBeanName : dependencies) {
destroySingleton(dependentBeanName);
}
}
//2. 真正销毁该 beanName
if (bean != null) {
try {
bean.destroy();
}
catch (Throwable ex) {
logger.error("Destroy method on bean with name '" + beanName + "' threw an exception", ex);
}
}
//3. 销毁该 beanName 所包含的子 containedBean
Set<String> containedBeans = this.containedBeanMap.remove(beanName);
if (containedBeans != null) {
for (String containedBeanName : containedBeans) {
destroySingleton(containedBeanName);
}
}
//4. 从其它 bean 的依赖 bean 集合中删除已销毁的 beanName
synchronized (this.dependentBeanMap) {
for (Iterator<Map.Entry<String, Set<String>>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {
Map.Entry<String, Set<String>> entry = it.next();
Set<String> dependenciesToClean = entry.getValue();
dependenciesToClean.remove(beanName);
if (dependenciesToClean.isEmpty()) {
it.remove();
}
}
}
//5. 最后从 dependenciesForBeanMap 缓存中移除要销毁的 bean
this.dependenciesForBeanMap.remove(beanName);
}
// 将所有的单例暴露给子类和外部
protected final Object getSingletonMutex() {
return this.singletonObjects;
}
}