FactoryBean for RMI proxies, supporting both conventional RMI services
and RMI invokers. Exposes the proxied service for use as a bean reference,
using the specified service interface. Proxies will throw Spring's unchecked
RemoteAccessException on remote invocation failure instead of RMI's RemoteException.
The service URL must be a valid RMI URL like "rmi://localhost:1099/myservice".
RMI invokers work at the RmiInvocationHandler level, using the same invoker stub
for any service. Service interfaces do not have to extend java.rmi.Remote
or throw java.rmi.RemoteException. Of course, in and out parameters
have to be serializable.
With conventional RMI services, this proxy factory is typically used with the
RMI service interface. Alternatively, this factory can also proxy a remote RMI
service with a matching non-RMI business interface, i.e. an interface that mirrors
the RMI service methods but does not declare RemoteExceptions. In the latter case,
RemoteExceptions thrown by the RMI stub will automatically get converted to
Spring's unchecked RemoteAccessException.
The major advantage of RMI, compared to Hessian, is serialization.
Effectively, any serializable Java object can be transported without hassle.
Hessian has its own (de-)serialization mechanisms, but is HTTP-based and thus
much easier to setup than RMI. Alternatively, consider Spring's HTTP invoker
to combine Java serialization with HTTP-based transport.
Return an instance (possibly shared or independent) of the object
managed by this factory.
As with a BeanFactory, this allows support for both the
Singleton and Prototype design pattern.
If this FactoryBean is not fully initialized yet at the time of
the call (for example because it is involved in a circular reference),
throw a corresponding FactoryBeanNotInitializedException.
As of Spring 2.0, FactoryBeans are allowed to return null
objects. The factory will consider this as normal value to be used; it
will not throw a FactoryBeanNotInitializedException in this case anymore.
FactoryBean implementations are encouraged to throw
FactoryBeanNotInitializedException themselves now, as appropriate.
Return the type of object that this FactoryBean creates,
or null if not known in advance.
This allows one to check for specific types of beans without
instantiating objects, for example on autowiring.
In the case of implementations that are creating a singleton object,
this method should try to avoid singleton creation as far as possible;
it should rather estimate the type in advance.
For prototypes, returning a meaningful type here is advisable too.
This method can be called before this FactoryBean has
been fully initialized. It must not rely on state created during
initialization; of course, it can still use such state if available.
NOTE: Autowiring will simply ignore FactoryBeans that return
null here. Therefore it is highly recommended to implement
this method properly, using the current state of the FactoryBean.
Is the object managed by this factory a singleton? That is,
will FactoryBean.getObject() always return the same object
(a reference that can be cached)?
NOTE: If a FactoryBean indicates to hold a singleton object,
the object returned from getObject() might get cached
by the owning BeanFactory. Hence, do not return true
unless the FactoryBean always exposes the same reference.
The singleton status of the FactoryBean itself will generally
be provided by the owning BeanFactory; usually, it has to be
defined as singleton there.
NOTE: This method returning false does not
necessarily indicate that returned objects are independent instances.
An implementation of the extended SmartFactoryBean interface
may explicitly indicate independent instances through its
SmartFactoryBean.isPrototype() method. Plain FactoryBean
implementations which do not implement this extended interface are
simply assumed to always return independent instances if the
isSingleton() implementation returns false.
The default implementation returns true, since a
FactoryBean typically manages a singleton instance.