org.springframework.beans.factory.config
Class ServiceLocatorFactoryBean

java.lang.Object
  extended by org.springframework.beans.factory.config.ServiceLocatorFactoryBean
All Implemented Interfaces:
BeanFactoryAware, FactoryBean<java.lang.Object>, InitializingBean

public class ServiceLocatorFactoryBean
extends java.lang.Object
implements FactoryBean<java.lang.Object>, BeanFactoryAware, InitializingBean

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.

Since:
1.1.4
Author:
Colin Sampaleanu, Juergen Hoeller
See Also:
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  java.lang.Exception createServiceLocatorException(java.lang.reflect.Constructor exceptionConstructor, BeansException cause)
          Create a service locator exception for the given cause.
protected  java.lang.reflect.Constructor determineServiceLocatorExceptionConstructor(java.lang.Class exceptionClass)
          Determine the constructor to use for the given service locator exception class.
 java.lang.Object getObject()
          Return an instance (possibly shared or independent) of the object managed by this factory.
 java.lang.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? That is, will FactoryBean.getObject() always return the same object (a reference that can be cached)?
 void setBeanFactory(BeanFactory beanFactory)
          Callback that supplies the owning factory to a bean instance.
 void setServiceLocatorExceptionClass(java.lang.Class serviceLocatorExceptionClass)
          Set the exception class that the service locator should throw if service lookup failed.
 void setServiceLocatorInterface(java.lang.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(java.util.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

ServiceLocatorFactoryBean

public ServiceLocatorFactoryBean()
Method Detail

setServiceLocatorInterface

public void setServiceLocatorInterface(java.lang.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)). See the class-level Javadoc for information on the semantics of such methods.


setServiceLocatorExceptionClass

public void setServiceLocatorExceptionClass(java.lang.Class serviceLocatorExceptionClass)
Set the exception class that the service locator should throw if service lookup failed. The specified exception class must have a constructor with one of the following parameter types: (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.

See Also:
determineServiceLocatorExceptionConstructor(java.lang.Class), createServiceLocatorException(java.lang.reflect.Constructor, org.springframework.beans.BeansException)

setServiceMappings

public void setServiceMappings(java.util.Properties serviceMappings)
Set mappings between service ids (passed into the service locator) and bean names (in the bean factory). Service ids that are not defined here will be treated as bean names as-is.

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.

Parameters:
serviceMappings - mappings between service ids and bean names, with service ids as keys as bean names as values

setBeanFactory

public void setBeanFactory(BeanFactory beanFactory)
                    throws BeansException
Description copied from interface: BeanFactoryAware
Callback that supplies the owning factory to a bean instance.

Invoked after the population of normal bean properties but before an initialization callback such as InitializingBean.afterPropertiesSet() or a custom init-method.

Specified by:
setBeanFactory in interface BeanFactoryAware
Parameters:
beanFactory - owning BeanFactory (never null). The bean can immediately call methods on the factory.
Throws:
BeansException - in case of initialization errors
See Also:
BeanInitializationException

afterPropertiesSet

public void afterPropertiesSet()
Description copied from interface: InitializingBean
Invoked by a BeanFactory after it has set all bean properties supplied (and satisfied BeanFactoryAware and ApplicationContextAware).

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.

Specified by:
afterPropertiesSet in interface InitializingBean

determineServiceLocatorExceptionConstructor

protected java.lang.reflect.Constructor determineServiceLocatorExceptionConstructor(java.lang.Class exceptionClass)
Determine the constructor to use for the given service locator exception class. Only called in case of a custom service locator exception.

The default implementation looks for a constructor with one of the following parameter types: (String, Throwable) or (Throwable) or (String).

Parameters:
exceptionClass - the exception class
Returns:
the constructor to use
See Also:
setServiceLocatorExceptionClass(java.lang.Class)

createServiceLocatorException

protected java.lang.Exception createServiceLocatorException(java.lang.reflect.Constructor exceptionConstructor,
                                                            BeansException cause)
Create a service locator exception for the given cause. Only called in case of a custom service locator exception.

The default implementation can handle all variations of message and exception arguments.

Parameters:
exceptionConstructor - the constructor to use
cause - the cause of the service lookup failure
Returns:
the service locator exception to throw
See Also:
setServiceLocatorExceptionClass(java.lang.Class)

getObject

public java.lang.Object getObject()
Description copied from interface: FactoryBean
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.

Specified by:
getObject in interface FactoryBean<java.lang.Object>
Returns:
an instance of the bean (can be null)
See Also:
FactoryBeanNotInitializedException

getObjectType

public java.lang.Class<?> getObjectType()
Description copied from interface: FactoryBean
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.

Specified by:
getObjectType in interface FactoryBean<java.lang.Object>
Returns:
the type of object that this FactoryBean creates, or null if not known at the time of the call
See Also:
ListableBeanFactory.getBeansOfType(java.lang.Class)

isSingleton

public boolean isSingleton()
Description copied from interface: 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.

Specified by:
isSingleton in interface FactoryBean<java.lang.Object>
Returns:
whether the exposed object is a singleton
See Also:
FactoryBean.getObject(), SmartFactoryBean.isPrototype()