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java.lang.Object org.springframework.beans.factory.config.ServiceLocatorFactoryBean
public class ServiceLocatorFactoryBean
A FactoryBean
implementation that
takes an interface which must have one or more methods with
the signatures MyType xxx()
or MyType xxx(MyIdType id)
(typically, MyService getService()
or MyService getService(String id)
)
and creates a dynamic proxy which implements that interface, delegating to an
underlying BeanFactory
.
Such service locators permit the decoupling of calling code from
the BeanFactory
API, by using an
appropriate custom locator interface. They will typically be used for
prototype beans, i.e. for factory methods that are supposed to
return a new instance for each call. The client receives a reference to the
service locator via setter or constructor injection, to be able to invoke
the locator's factory methods on demand. For singleton beans, direct
setter or constructor injection of the target bean is preferable.
On invocation of the no-arg factory method, or the single-arg factory
method with a String id of null
or empty String, if exactly
one bean in the factory matches the return type of the factory
method, that bean is returned, otherwise a
NoSuchBeanDefinitionException
is thrown.
On invocation of the single-arg factory method with a non-null (and
non-empty) argument, the proxy returns the result of a
BeanFactory.getBean(String)
call,
using a stringified version of the passed-in id as bean name.
A factory method argument will usually be a String, but can also be an
int or a custom enumeration type, for example, stringified via
toString
. The resulting String can be used as bean name as-is,
provided that corresponding beans are defined in the bean factory.
Alternatively, a custom mapping
between service ids and bean names can be defined.
By way of an example, consider the following service locator interface. Note that this interface is not dependant on any Spring APIs.
package a.b.c; public interface ServiceFactory { public MyService getService (); }
A sample config in an XML-based
BeanFactory
might look as follows:
<beans> <!-- Prototype bean since we have state --> <bean id="myService" class="a.b.c.MyService" singleton="false"/> <!-- will lookup the above 'myService' bean by *TYPE* --> <bean id="myServiceFactory" class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean"> <property name="serviceLocatorInterface" value="a.b.c.ServiceFactory"/> </bean> <bean id="clientBean" class="a.b.c.MyClientBean"> <property name="myServiceFactory" ref="myServiceFactory"/> </bean> </beans>
The attendant MyClientBean
class implementation might then
look something like this:
package a.b.c; public class MyClientBean { private ServiceFactory myServiceFactory; // actual implementation provided by the Spring container public void setServiceFactory(ServiceFactory myServiceFactory) { this.myServiceFactory = myServiceFactory; } public void someBusinessMethod() { // get a 'fresh', brand new MyService instance MyService service = this.myServiceFactory.getService(); // use the service object to effect the business logic... } }
By way of an example that looks up a bean by name, consider the following service locator interface. Again, note that this interface is not dependant on any Spring APIs.
package a.b.c; public interface ServiceFactory { public MyService getService (String serviceName); }
A sample config in an XML-based
BeanFactory
might look as follows:
<beans> <!-- Prototype beans since we have state (both extend MyService) --> <bean id="specialService" class="a.b.c.SpecialService" singleton="false"/> <bean id="anotherService" class="a.b.c.AnotherService" singleton="false"/> <bean id="myServiceFactory" class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean"> <property name="serviceLocatorInterface" value="a.b.c.ServiceFactory"/> </bean> <bean id="clientBean" class="a.b.c.MyClientBean"> <property name="myServiceFactory" ref="myServiceFactory"/> </bean> </beans>
The attendant MyClientBean
class implementation might then
look something like this:
package a.b.c; public class MyClientBean { private ServiceFactory myServiceFactory; // actual implementation provided by the Spring container public void setServiceFactory(ServiceFactory myServiceFactory) { this.myServiceFactory = myServiceFactory; } public void someBusinessMethod() { // get a 'fresh', brand new MyService instance MyService service = this.myServiceFactory.getService("specialService"); // use the service object to effect the business logic... } public void anotherBusinessMethod() { // get a 'fresh', brand new MyService instance MyService service = this.myServiceFactory.getService("anotherService"); // use the service object to effect the business logic... } }
See ObjectFactoryCreatingFactoryBean
for an alternate approach.
setServiceLocatorInterface(java.lang.Class)
,
setServiceMappings(java.util.Properties)
,
ObjectFactoryCreatingFactoryBean
Constructor Summary | |
---|---|
ServiceLocatorFactoryBean()
|
Method Summary | |
---|---|
void |
afterPropertiesSet()
Invoked by a BeanFactory after it has set all bean properties supplied (and satisfied BeanFactoryAware and ApplicationContextAware). |
protected Exception |
createServiceLocatorException(Constructor exceptionConstructor,
BeansException cause)
Create a service locator exception for the given cause. |
protected Constructor |
determineServiceLocatorExceptionConstructor(Class exceptionClass)
Determine the constructor to use for the given service locator exception class. |
Object |
getObject()
Return an instance (possibly shared or independent) of the object managed by this factory. |
Class |
getObjectType()
Return the type of object that this FactoryBean creates, or null if not known in advance. |
boolean |
isSingleton()
Is the object managed by this factory a singleton? |
void |
setBeanFactory(BeanFactory beanFactory)
Callback that supplies the owning factory to a bean instance. |
void |
setServiceLocatorExceptionClass(Class serviceLocatorExceptionClass)
Set the exception class that the service locator should throw if service lookup failed. |
void |
setServiceLocatorInterface(Class interfaceType)
Set the service locator interface to use, which must have one or more methods with the signatures MyType xxx() or MyType xxx(MyIdType id)
(typically, MyService getService() or MyService getService(String id) ). |
void |
setServiceMappings(Properties serviceMappings)
Set mappings between service ids (passed into the service locator) and bean names (in the bean factory). |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
---|
public ServiceLocatorFactoryBean()
Method Detail |
---|
public void setServiceLocatorInterface(Class interfaceType)
MyType xxx()
or MyType xxx(MyIdType id)
(typically, MyService getService()
or MyService getService(String id)
).
See the class-level Javadoc
for
information on the semantics of such methods.
interfaceType
- the Class
of the interface to be used for the service locatorpublic void setServiceLocatorExceptionClass(Class serviceLocatorExceptionClass)
(String, Throwable)
or (Throwable)
or (String)
.
If not specified, subclasses of Spring's BeansException will be thrown, for example NoSuchBeanDefinitionException. As those are unchecked, the caller does not need to handle them, so it might be acceptable that Spring exceptions get thrown as long as they are just handled generically.
public void setServiceMappings(Properties serviceMappings)
The empty string as service id key defines the mapping for null
and
empty string, and for factory methods without parameter. If not defined,
a single matching bean will be retrieved from the bean factory.
serviceMappings
- mappings between service ids and bean names,
with service ids as keys as bean names as valuespublic void setBeanFactory(BeanFactory beanFactory) throws BeansException
BeanFactoryAware
Invoked after the population of normal bean properties
but before an initialization callback such as
InitializingBean.afterPropertiesSet()
or a custom init-method.
setBeanFactory
in interface BeanFactoryAware
beanFactory
- owning BeanFactory (never null
).
The bean can immediately call methods on the factory.
BeansException
- in case of initialization errorsBeanInitializationException
public void afterPropertiesSet()
InitializingBean
This method allows the bean instance to perform initialization only possible when all bean properties have been set and to throw an exception in the event of misconfiguration.
afterPropertiesSet
in interface InitializingBean
protected Constructor determineServiceLocatorExceptionConstructor(Class exceptionClass)
The default implementation looks for a constructor with one of the
following parameter types: (String, Throwable)
or (Throwable)
or (String)
.
exceptionClass
- the exception class
setServiceLocatorExceptionClass(java.lang.Class)
protected Exception createServiceLocatorException(Constructor exceptionConstructor, BeansException cause)
The default implementation can handle all variations of message and exception arguments.
exceptionConstructor
- the constructor to usecause
- the cause of the service lookup failure
setServiceLocatorExceptionClass(java.lang.Class)
public Object getObject()
FactoryBean
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.
getObject
in interface FactoryBean
null
)FactoryBeanNotInitializedException
public Class getObjectType()
FactoryBean
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.
getObjectType
in interface FactoryBean
null
if not known at the time of the callListableBeanFactory.getBeansOfType(java.lang.Class)
public boolean isSingleton()
FactoryBean
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
.
isSingleton
in interface FactoryBean
FactoryBean.getObject()
,
SmartFactoryBean.isPrototype()
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