public boolean containsSingleton(String beanName)
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 #registerSingleton ). 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.

 public Object getSingleton(String beanName)
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 #registerSingleton ). Can also be used to access a singleton
defined by a bean definition that already been created, in a raw fashion.

 public int getSingletonCount()
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 #registerSingleton ). Can also be used to count the number of
singletons defined by a bean definition that have already been created.

 public String[] getSingletonNames()
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 #registerSingleton ). Can also be used to check which
singletons defined by a bean definition have already been created.

 public  void registerSingleton(String beanName,
    Object singletonObject)
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.