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## org.springframework.beans.factory.support
Class DefaultSingletonBeanRegistry

    java.lang.Object
      org.springframework.core.SimpleAliasRegistry
          org.springframework.beans.factory.support.DefaultSingletonBeanRegistry

All Implemented Interfaces:
  SingletonBeanRegistry, AliasRegistry

Direct Known Subclasses:
  FactoryBeanRegistrySupport

    public class DefaultSingletonBeanRegistry

extends SimpleAliasRegistry
implements SingletonBeanRegistry

Generic registry for shared bean instances, implementing the `SingletonBeanRegistry`. Allows for registering singleton instances that should be shared for all callers of the registry, to be obtained via bean name.

Also supports registration of `DisposableBean` instances, (which might or might not correspond to registered singletons), to be destroyed on shutdown of the registry. Dependencies between beans can be registered to enforce an appropriate shutdown order.

This class mainly serves as base class for `BeanFactory` implementations, factoring out the common management of singleton bean instances. Note that the `ConfigurableBeanFactory` interface extends the `SingletonBeanRegistry` interface.

Note that this class assumes neither a bean definition concept nor a specific creation process for bean instances, in contrast to `AbstractBeanFactory` and `DefaultListableBeanFactory` (which inherit from it). Can alternatively also be used as a nested helper to delegate to.

Since:
  2.0
Author:
  Juergen Hoeller
See Also:
  `registerSingleton(java.lang.String, java.lang.Object)`, `registerDisposableBean(java.lang.String, org.springframework.beans.factory.DisposableBean)`, `DisposableBean`, `ConfigurableBeanFactory`

Field Summary
`protected Log` | `logger` Logger available to subclasses
`protected static Object` | `NULL_OBJECT` Internal marker for a null singleton object: used as marker value for concurrent Maps (which don't support null values).

Constructor Summary
`DefaultSingletonBeanRegistry()`

Method Summary
`protected void` | `addSingleton(String beanName, Object singletonObject)` Add the given singleton object to the singleton cache of this factory.
`protected void` | `addSingletonFactory(String beanName, ObjectFactory singletonFactory)` Add the given singleton factory for building the specified singleton if necessary.
`protected void` | `afterSingletonCreation(String beanName)` Callback after singleton creation.
`protected void` | `beforeSingletonCreation(String beanName)` Callback before singleton creation.
`boolean` | `containsSingleton(String beanName)` Check if this registry contains a singleton instance with the given name.
`protected void` | `destroyBean(String beanName, DisposableBean bean)` Destroy the given bean.
`void` | `destroySingleton(String beanName)` Destroy the given bean.
`void` | `destroySingletons()`
`String[]` | `getDependenciesForBean(String beanName)` Return the names of all beans that the specified bean depends on, if any.
`String[]` | `getDependentBeans(String beanName)` Return the names of all beans which depend on the specified bean, if any.
`Object` | `getSingleton(String beanName)` Return the (raw) singleton object registered under the given name.
`protected Object` | `getSingleton(String beanName, boolean allowEarlyReference)` Return the (raw) singleton object registered under the given name.
`Object` | `getSingleton(String beanName, ObjectFactory singletonFactory)` Return the (raw) singleton object registered under the given name, creating and registering a new one if none registered yet.
`int` | `getSingletonCount()` Return the number of singleton beans registered in this registry.
`protected Object` | `getSingletonMutex()` Expose the singleton mutex to subclasses.
`String[]` | `getSingletonNames()` Return the names of singleton beans registered in this registry.
`protected boolean` | `hasDependentBean(String beanName)` Determine whether a dependent bean has been registered under the given name.
`boolean` | `isSingletonCurrentlyInCreation(String beanName)` Return whether the specified singleton bean is currently in creation (within the entire factory).
`protected void` | `onSuppressedException(Exception ex)` Register an Exception that happened to get suppressed during the creation of a singleton bean instance, e.g. a temporary circular reference resolution problem.
`void` | `registerDependentBean(String beanName, String dependentBeanName)` Register a dependent bean for the given bean, to be destroyed before the given bean is destroyed.
`void` | `registerDisposableBean(String beanName, DisposableBean bean)` Add the given bean to the list of disposable beans in this registry.
`void` | `registerSingleton(String beanName, Object singletonObject)` Register the given existing object as singleton in the bean registry, under the given bean name.
`protected void` | `removeSingleton(String beanName)` Remove the bean with the given name from the singleton cache of this factory, to be able to clean up eager registration of a singleton if creation failed.

Methods inherited from class org.springframework.core.SimpleAliasRegistry
`allowAliasOverriding, canonicalName, getAliases, isAlias, registerAlias, removeAlias, resolveAliases`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### NULL_OBJECT

    protected static final Object NULL_OBJECT

  Internal marker for a null singleton object: used as marker value for concurrent Maps (which don't support null values).

### logger

    protected final Log logger

  Logger available to subclasses

Constructor Detail

### DefaultSingletonBeanRegistry

    public DefaultSingletonBeanRegistry()

Method Detail

### registerSingleton

    public void registerSingleton(String beanName,
                                  Object singletonObject)
                           throws IllegalStateException

  Description copied from interface: `SingletonBeanRegistry`
  Register the given existing object as singleton in the bean registry, under the given bean name.

  The given instance is supposed to be fully initialized; the registry will not perform any initialization callbacks (in particular, it won't call InitializingBean's `afterPropertiesSet` method). The given instance will not receive any destruction callbacks (like DisposableBean's `destroy` method) either.

  If running within a full BeanFactory: Register a bean definition instead of an existing instance if your bean is supposed to receive initialization and/or destruction callbacks.

  Typically invoked during registry configuration, but can also be used for runtime registration of singletons. As a consequence, a registry implementation should synchronize singleton access; it will have to do this anyway if it supports a BeanFactory's lazy initialization of singletons.

  Specified by:
    `registerSingleton` in interface `SingletonBeanRegistry`
  Parameters:
    `beanName` - the name of the bean
    `singletonObject` - the existing singleton object
  Throws:
    `IllegalStateException`
  See Also:
    `InitializingBean.afterPropertiesSet()`, `DisposableBean.destroy()`, `BeanDefinitionRegistry.registerBeanDefinition(java.lang.String, org.springframework.beans.factory.config.BeanDefinition)`

### addSingleton

    protected void addSingleton(String beanName,
                                Object singletonObject)

  Add the given singleton object to the singleton cache of this factory.

  To be called for eager registration of singletons.

  Parameters:
    `beanName` - the name of the bean
    `singletonObject` - the singleton object

### addSingletonFactory

    protected void addSingletonFactory(String beanName,
                                       ObjectFactory singletonFactory)

  Add the given singleton factory for building the specified singleton if necessary.

  To be called for eager registration of singletons, e.g. to be able to resolve circular references.

  Parameters:
    `beanName` - the name of the bean
    `singletonFactory` - the factory for the singleton object

### getSingleton

    public Object getSingleton(String beanName)

  Description copied from interface: `SingletonBeanRegistry`
  Return the (raw) singleton object registered under the given name.

  Only checks already instantiated singletons; does not return an Object for singleton bean definitions which have not been instantiated yet.

  The main purpose of this method is to access manually registered singletons (see `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`). Can also be used to access a singleton defined by a bean definition that already been created, in a raw fashion.

  Specified by:
    `getSingleton` in interface `SingletonBeanRegistry`
  Parameters:
    `beanName` - the name of the bean to look for
  Returns:
    the registered singleton object, or `null` if none found
  See Also:
    `ConfigurableListableBeanFactory.getBeanDefinition(java.lang.String)`

### getSingleton

    protected Object getSingleton(String beanName,
                                  boolean allowEarlyReference)

  Return the (raw) singleton object registered under the given name.

  Checks already instantiated singletons and also allows for an early reference to a currently created singleton (resolving a circular reference).

  Parameters:
    `beanName` - the name of the bean to look for
    `allowEarlyReference` - whether early references should be created or not
  Returns:
    the registered singleton object, or `null` if none found

### getSingleton

    public Object getSingleton(String beanName,
                               ObjectFactory singletonFactory)

  Return the (raw) singleton object registered under the given name, creating and registering a new one if none registered yet.

  Parameters:
    `beanName` - the name of the bean
    `singletonFactory` - the ObjectFactory to lazily create the singleton with, if necessary
  Returns:
    the registered singleton object

### onSuppressedException

    protected void onSuppressedException(Exception ex)

  Register an Exception that happened to get suppressed during the creation of a singleton bean instance, e.g. a temporary circular reference resolution problem.

  Parameters:
    `ex` - the Exception to register

### removeSingleton

    protected void removeSingleton(String beanName)

  Remove the bean with the given name from the singleton cache of this factory, to be able to clean up eager registration of a singleton if creation failed.

  Parameters:
    `beanName` - the name of the bean
  See Also:
    `getSingletonMutex()`

### containsSingleton

    public boolean containsSingleton(String beanName)

  Description copied from interface: `SingletonBeanRegistry`
  Check if this registry contains a singleton instance with the given name.

  Only checks already instantiated singletons; does not return `true` for singleton bean definitions which have not been instantiated yet.

  The main purpose of this method is to check manually registered singletons (see `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`). Can also be used to check whether a singleton defined by a bean definition has already been created.

  To check whether a bean factory contains a bean definition with a given name, use ListableBeanFactory's `containsBeanDefinition`. Calling both `containsBeanDefinition` and `containsSingleton` answers whether a specific bean factory contains an own bean with the given name.

  Use BeanFactory's `containsBean` for general checks whether the factory knows about a bean with a given name (whether manually registered singleton instance or created by bean definition), also checking ancestor factories.

  Specified by:
    `containsSingleton` in interface `SingletonBeanRegistry`
  Parameters:
    `beanName` - the name of the bean to look for
  Returns:
    if this bean factory contains a singleton instance with the given name
  See Also:
    `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`, `ListableBeanFactory.containsBeanDefinition(java.lang.String)`, `BeanFactory.containsBean(java.lang.String)`

### getSingletonNames

    public String[] getSingletonNames()

  Description copied from interface: `SingletonBeanRegistry`
  Return the names of singleton beans registered in this registry.

  Only checks already instantiated singletons; does not return names for singleton bean definitions which have not been instantiated yet.

  The main purpose of this method is to check manually registered singletons (see `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`). Can also be used to check which singletons defined by a bean definition have already been created.

  Specified by:
    `getSingletonNames` in interface `SingletonBeanRegistry`
  Returns:
    the list of names as String array (never `null`)
  See Also:
    `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`, `BeanDefinitionRegistry.getBeanDefinitionNames()`, `ListableBeanFactory.getBeanDefinitionNames()`

### getSingletonCount

    public int getSingletonCount()

  Description copied from interface: `SingletonBeanRegistry`
  Return the number of singleton beans registered in this registry.

  Only checks already instantiated singletons; does not count singleton bean definitions which have not been instantiated yet.

  The main purpose of this method is to check manually registered singletons (see `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`). Can also be used to count the number of singletons defined by a bean definition that have already been created.

  Specified by:
    `getSingletonCount` in interface `SingletonBeanRegistry`
  Returns:
    the number of singleton beans
  See Also:
    `SingletonBeanRegistry.registerSingleton(java.lang.String, java.lang.Object)`, `BeanDefinitionRegistry.getBeanDefinitionCount()`, `ListableBeanFactory.getBeanDefinitionCount()`

### beforeSingletonCreation

    protected void beforeSingletonCreation(String beanName)

  Callback before singleton creation.

  Default implementation register the singleton as currently in creation.

  Parameters:
    `beanName` - the name of the singleton about to be created
  See Also:
    `isSingletonCurrentlyInCreation(java.lang.String)`

### afterSingletonCreation

    protected void afterSingletonCreation(String beanName)

  Callback after singleton creation.

  Default implementation marks the singleton as not in creation anymore.

  Parameters:
    `beanName` - the name of the singleton that has been created
  See Also:
    `isSingletonCurrentlyInCreation(java.lang.String)`

### isSingletonCurrentlyInCreation

    public final boolean isSingletonCurrentlyInCreation(String beanName)

  Return whether the specified singleton bean is currently in creation (within the entire factory).

  Parameters:
    `beanName` - the name of the bean

### registerDisposableBean

    public void registerDisposableBean(String beanName,
                                       DisposableBean bean)

  Add the given bean to the list of disposable beans in this registry. Disposable beans usually correspond to registered singletons, matching the bean name but potentially being a different instance (for example, a DisposableBean adapter for a singleton that does not naturally implement Spring's DisposableBean interface).

  Parameters:
    `beanName` - the name of the bean
    `bean` - the bean instance

### registerDependentBean

    public void registerDependentBean(String beanName,
                                      String dependentBeanName)

  Register a dependent bean for the given bean, to be destroyed before the given bean is destroyed.

  Parameters:
    `beanName` - the name of the bean
    `dependentBeanName` - the name of the dependent bean

### hasDependentBean

    protected boolean hasDependentBean(String beanName)

  Determine whether a dependent bean has been registered under the given name.

  Parameters:
    `beanName` - the name of the bean

### getDependentBeans

    public String[] getDependentBeans(String beanName)

  Return the names of all beans which depend on the specified bean, if any.

  Parameters:
    `beanName` - the name of the bean
  Returns:
    the array of dependent bean names, or an empty array if none

### getDependenciesForBean

    public String[] getDependenciesForBean(String beanName)

  Return the names of all beans that the specified bean depends on, if any.

  Parameters:
    `beanName` - the name of the bean
  Returns:
    the array of names of beans which the bean depends on, or an empty array if none

### destroySingletons

    public void destroySingletons()

### destroySingleton

    public void destroySingleton(String beanName)

  Destroy the given bean. Delegates to `destroyBean` if a corresponding disposable bean instance is found.

  Parameters:
    `beanName` - the name of the bean
  See Also:
    `destroyBean(java.lang.String, org.springframework.beans.factory.DisposableBean)`

### destroyBean

    protected void destroyBean(String beanName,
                               DisposableBean bean)

  Destroy the given bean. Must destroy beans that depend on the given bean before the bean itself. Should not throw any exceptions.

  Parameters:
    `beanName` - the name of the bean
    `bean` - the bean instance to destroy

### getSingletonMutex

    protected final Object getSingletonMutex()

  Expose the singleton mutex to subclasses.

  Subclasses should synchronize on the given Object if they perform any sort of extended singleton creation phase. In particular, subclasses should not have their own mutexes involved in singleton creation, to avoid the potential for deadlocks in lazy-init situations.

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