org.springframework.beans.factory.config

## Class ServiceLocatorFactoryBean

- java.lang.Object
- - org.springframework.beans.factory.config.ServiceLocatorFactoryBean

- All Implemented Interfaces:
    Aware, BeanFactoryAware, FactoryBean<Object>, InitializingBean

      public class ServiceLocatorFactoryBean
      extends Object
      implements FactoryBean<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

    Constructors
    Constructor and Description
    `ServiceLocatorFactoryBean()`

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `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? 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(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

    - #### ServiceLocatorFactoryBean

          public ServiceLocatorFactoryBean()

  - ### Method Detail

    - #### setServiceLocatorInterface

          public 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)`). See the `class-level Javadoc` for information on the semantics of such methods.

    - #### setServiceLocatorExceptionClass

          public void setServiceLocatorExceptionClass(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(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 Constructor determineServiceLocatorExceptionConstructor(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 Exception createServiceLocatorException(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 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<Object>`
      Returns:
        an instance of the bean (can be `null`)
      See Also:
        `FactoryBeanNotInitializedException`

    - #### getObjectType

          public 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<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<T>)`

    - #### 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<Object>`
      Returns:
        whether the exposed object is a singleton
      See Also:
        `FactoryBean.getObject()`, `SmartFactoryBean.isPrototype()`