这是DefaultSingletonBeanRegistry类的体系结构,由一个类一个责任的原则
- AliasRegistry : 提供别名注册的接口
- SingletonBeanRegistry : 提供单例bean注册的接口
- 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）.
- 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。
- SimpleAliasRegistry: 它简单地实现了AliasRegistry接口。
- 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)。
/**
* 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 {
//内部标记为一个空的单例对象： 并发 Maps( 不支持空值 )作为标志值。
protected static final Object NULL_OBJECT = new Object();
// 日记用来记录子类
protected final Log logger = LogFactory.getLog(getClass());
//是存放singleton对象的缓存
private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>();
// 是存放制造singleton的工厂对象的缓存
private final Map<String, ObjectFactory> singletonFactories = new HashMap<String, ObjectFactory>();
//是存放singletonFactory 制造出来的 singleton 的缓存
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>());
//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与被包含在外部bean的所有内部bean集合包含关系的缓存
private final Map<String, Set<String>> containedBeanMap = new ConcurrentHashMap<String, Set<String>>();
//指定bean与依赖指定bean的所有bean的依赖关系的缓存
private final Map<String, Set<String>> dependentBeanMap = new ConcurrentHashMap<String, Set<String>>();
//指定bean与创建这个bean所需要依赖的所有bean的依赖关系的缓存
private final Map<String, Set<String>> dependenciesForBeanMap = new ConcurrentHashMap<String, Set<String>>();
// 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，则表示该名称已被占用
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));
// beanName已被注册存放在singletonObjects缓存，那么singletonFactories不应该再持有名称为beanName的工厂
this.singletonFactories.remove(beanName);
// beanName已被注册存放在singletonObjects缓存，那么earlySingletonObjects不应该再持有名称为beanName的bean。
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) {
// 判断singletonObjects内名字为beanName是否被占用，若没有，进行注册操作
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);
}
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
// 如果singletonObjects指定beanName的对象是不存在的
if (singletonObject == null) {
synchronized (this.singletonObjects) {
singletonObject = this.earlySingletonObjects.get(beanName);
// 如果earlySingletonObjects指定的beanName的对象是不存在的且allowEarlyReference是允许的
if (singletonObject == null && allowEarlyReference) {
ObjectFactory singletonFactory = this.singletonFactories
.get(beanName);
// 如果存在指定beanName的singletonFactory对象
if (singletonFactory != null) {
// singletonFactory创建指定的单例对象
singletonObject = singletonFactory.getObject();
// 这里可以看出earlySingletonObjects缓存应该是存放singletonFactory产生的singleton
this.earlySingletonObjects.put(beanName,
singletonObject);
// 这里表示指定的beanName已被占用，所以要在singletonFactories移除该名称
this.singletonFactories.remove(beanName);
}
}
}
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
public Object getSingleton(String beanName, ObjectFactory singletonFactory) {
Assert.notNull(beanName, "'beanName' must not be null");
synchronized (this.singletonObjects) {
Object singletonObject = this.singletonObjects.get(beanName);
// 如果singetonObjects缓存不存在名称为beanName的对象
if (singletonObject == null) {
// 如果目前在销毁singellton
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 + "'");
}
// 单例对象创建前的回调,默认实现注册正在创建的单例
beforeSingletonCreation(beanName);
// 判断存储异常相关原因的集合是否已存在
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
// 若没有，刚创建异常集合的实例
if (recordSuppressedExceptions) {
this.suppressedExceptions = new LinkedHashSet<Exception>();
}
try {
// 由参数给定的singletonFactory创建singleton对象,getObject方法的具体实现由ObjectFactory的子类决定
singletonObject = singletonFactory.getObject();
} catch (BeanCreationException ex) {
// 如果异常被抓取，在这里将出现异常的原因抛出
if (recordSuppressedExceptions) {
for (Exception suppressedException : this.suppressedExceptions) {
ex.addRelatedCause(suppressedException);
}
}
throw ex;
} finally {
// 结束前，将异常集合销毁掉
if (recordSuppressedExceptions) {
this.suppressedExceptions = null;
}
// 单例创建之后的回调,默认的实现标志单例不要在创建了。
afterSingletonCreation(beanName);
}
// 注册创建后的单例
addSingleton(beanName, singletonObject);
}
return (singletonObject != NULL_OBJECT ? singletonObject : null);
}
}
/**
* 注册 发生在singeton bean 实例创建之间发生的异常
*/
protected void onSuppressedException(Exception ex) {
synchronized (this.singletonObjects) {
if (this.suppressedExceptions != null) {
this.suppressedExceptions.add(ex);
}
}
}
/**
* 移除名称为beanName的单例,主要在四个集合中移除，
* 如singletonObjects,singletonFactories,earlySingletonObjects
* ,registeredSingletons
*
*/
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();
}
}
/**
* 单例对象创建前的回调,默认实现singletonsCurrentlyInCreation集合注册正在创建的单例.
*
*/
protected void beforeSingletonCreation(String beanName) {
if (!this.singletonsCurrentlyInCreation.add(beanName)) {
throw new BeanCurrentlyInCreationException(beanName);
}
}
/**
* 单例创建之后的回调,默认实现singletonCurrentlyInCreation集合移除正在创建的单例
*
*/
protected void afterSingletonCreation(String beanName) {
if (!this.singletonsCurrentlyInCreation.remove(beanName)) {
throw new IllegalStateException("Singleton '" + beanName
+ "' isn't currently in creation");
}
}
/**
* 返回 存放正在创建单例的集合是否包含指定名称为beanName的单例存在
*
*/
public final boolean isSingletonCurrentlyInCreation(String beanName) {
return this.singletonsCurrentlyInCreation.contains(beanName);
}
/**
* 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,例如内部bean和包含其的外部bean之间
*
*/
public void registerContainedBean(String containedBeanName,
String containingBeanName) {
synchronized (this.containedBeanMap) {
// 从containedBeanMap缓存中查找外部bean名为containingBeanName的内部bean集合
Set<String> containedBeans = this.containedBeanMap
.get(containingBeanName);
// 如果没有，刚新建一个存放内部bean的集合，并且存放在containedBeanMap缓存中
if (containedBeans == null) {
containedBeans = new LinkedHashSet<String>(8);
this.containedBeanMap.put(containingBeanName, containedBeans);
}
// 将名为containedBeanName的内部bean存放到内部bean集合
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);
synchronized (this.dependentBeanMap) {
// 从dependentBeanMap缓存中找到依赖名为canonicalName这个bean的 依赖bean集合
Set<String> dependentBeans = this.dependentBeanMap
.get(canonicalName);
// 如果为空，则新建一个依赖bean集合，并且存放到dependentBeanMap缓存中
if (dependentBeans == null) {
dependentBeans = new LinkedHashSet<String>(8);
this.dependentBeanMap.put(canonicalName, dependentBeans);
}
// 依赖bean集合添加参数2指定的dependentBeanName
dependentBeans.add(dependentBeanName);
}
synchronized (this.dependenciesForBeanMap) {
// 从dependenciesForBeanMap缓存中找到dependentBeanName要依赖的所有bean集合
Set<String> dependenciesForBean = this.dependenciesForBeanMap
.get(dependentBeanName);
if (dependenciesForBean == null) {
dependenciesForBean = new LinkedHashSet<String>(8);
this.dependenciesForBeanMap.put(dependentBeanName,
dependenciesForBean);
}
dependenciesForBean.add(canonicalName);
}
}
/**
* 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。
*
*/
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。
*
*/
public String[] getDependenciesForBean(String beanName) {
Set<String> dependenciesForBean = this.dependenciesForBeanMap
.get(beanName);
// 如果没有的话返回new String[0]而不是null
if (dependenciesForBean == null) {
return new String[0];
}
return dependenciesForBean.toArray(new String[dependenciesForBean
.size()]);
}
// 销毁单例
public void destroySingletons() {
if (logger.isInfoEnabled()) {
logger.info("Destroying singletons in " + this);
}
// 单例目前销毁标志开始
synchronized (this.singletonObjects) {
this.singletonsCurrentlyInDestruction = true;
}
// 销毁disponsableBeans缓存中所有单例bean
synchronized (this.disposableBeans) {
String[] disposableBeanNames = StringUtils
.toStringArray(this.disposableBeans.keySet());
for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
destroySingleton(disposableBeanNames[i]);
}
}
// containedBeanMap缓存清空,dependentBeanMap缓存清空，dependenciesForBeanMap缓存清空
this.containedBeanMap.clear();
this.dependentBeanMap.clear();
this.dependenciesForBeanMap.clear();
// singeltonObjects缓存清空，singletonFactories缓存清空，earlySingletonObjects缓存清空，registeredSingletons缓存清空
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);
}
protected void destroyBean(String beanName, DisposableBean bean) {
// Trigger destruction of dependent beans first...
// 这段代码告诉我们先移除要销毁依赖bean
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);
}
}
// Actually destroy the bean now...
// 销毁bean实例
if (bean != null) {
try {
bean.destroy();
} catch (Throwable ex) {
logger.error("Destroy method on bean with name '" + beanName
+ "' threw an exception", ex);
}
}
// Trigger destruction of contained beans...
// 从containedBeanMap缓存中移除要销毁的bean，递归移除它的包含内部bean集合
Set<String> containedBeans = this.containedBeanMap.remove(beanName);
if (containedBeans != null) {
for (String containedBeanName : containedBeans) {
destroySingleton(containedBeanName);
}
}
// Remove destroyed bean from other beans' dependencies.
// 从其它bean的依赖bean集合中移除要销毁的bean
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();
}
}
}
// Remove destroyed bean's prepared dependency information.
// 最后 从dependenciesForBeanMap缓存中移除要销毁的bean
this.dependenciesForBeanMap.remove(beanName);
}
/**
* Expose the singleton mutex to subclasses.
* <p>
* Subclasses should synchronize on the given Object if they perform any
* sort of extended singleton creation phase. In particular, subclasses
* should <i>not</i> have their own mutexes involved in singleton creation,
* to avoid the potential for deadlocks in lazy-init situations.
*/
protected final Object getSingletonMutex() {
return this.singletonObjects;
}
}
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