DefaultSingletonBeanRegistry (Spring Framework 3.2.1.RELEASE API)
Date: 2013-01-24

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

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `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

    Constructors
    Constructor and Description
    `DefaultSingletonBeanRegistry()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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 for the given name.
    `protected boolean` | `isActuallyInCreation(String beanName)`
    `boolean` | `isCurrentlyInCreation(String beanName)`
    `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.
    `void` | `registerContainedBean(String containedBeanName, String containingBeanName)` Register a containment relationship between two beans, e.g.
    `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.
    `void` | `setCurrentlyInCreation(String beanName, boolean inCreation)`

    - ### Methods inherited from class org.springframework.core.SimpleAliasRegistry

      `allowAliasOverriding, canonicalName, checkForAliasCircle, 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.

      When 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.

      NOTE: This lookup method is not aware of FactoryBean prefixes or aliases. You need to resolve the canonical bean name first before obtaining the singleton instance.

      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 a local bean instance 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.

      NOTE: This lookup method is not aware of FactoryBean prefixes or aliases. You need to resolve the canonical bean name first before checking the singleton status.

      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 a 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()`

    - #### setCurrentlyInCreation

          public void setCurrentlyInCreation(String beanName,
                                    boolean inCreation)

    - #### isCurrentlyInCreation

          public boolean isCurrentlyInCreation(String beanName)

    - #### isActuallyInCreation

          protected boolean isActuallyInCreation(String beanName)

    - #### isSingletonCurrentlyInCreation

          public 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

    - #### 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.

      The 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)`

    - #### 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

    - #### registerContainedBean

          public void registerContainedBean(String containedBeanName,
                                   String containingBeanName)

      Register a containment relationship between two beans, e.g. between an inner bean and its containing outer bean.

      Also registers the containing bean as dependent on the contained bean in terms of destruction order.

      Parameters:
        `containedBeanName` - the name of the contained (inner) bean
        `containingBeanName` - the name of the containing (outer) bean
      See Also:
        `registerDependentBean(java.lang.String, java.lang.String)`

    - #### 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 for the given name.
      Parameters:
        `beanName` - the name of the bean to check

    - #### 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.