oracle.dbtools.plugin.api.di

Interface InstanceLocator

public interface InstanceLocator

Allows the application to dynamically obtain instances of services with a specified combination of required type and qualifiers. In general it is preferred to use injection to resolve dependencies, but in certain situations, injection is not the most convenient way to obtain a service instance. For these cases InstanceProvider should be used. This facility should be used sparingly, frequent use indicates use of the Service Locator Pattern instead of the Dependency Injection Pattern.

Author:

cdivilly

See Also:

InstanceProvider

Field Summary

Fields

Modifier and Type	Field and Description
static String	INSTANCE_LOCATOR_ATTRIBUTE Denotes the name of a HttpServletRequest attribute which if present on a request indicates an attribute whose value will be an instance of InstanceLocator

Method Summary

Modifier and Type	Method and Description
<T> InstanceProvider<T>	select(Class<T> instanceType, Annotation... qualifiers) Obtains a child Instance for the given required type and additional required qualifiers.

Field Detail

INSTANCE_LOCATOR_ATTRIBUTE

static final String INSTANCE_LOCATOR_ATTRIBUTE

Denotes the name of a HttpServletRequest attribute which if present on a request indicates an attribute whose value will be an instance of InstanceLocator

 void doGet(final HttpServletRequest request,
     final HttpServletResponse response)
     throws ServletException, IOException {
   // Get request scoped InstanceLocator
   final InstanceLocator locator = (InstanceLocator) request
       .getAttribute(InstanceLocator.INSTANCE_LOCATOR_ATTRIBUTE);
   if (locator != null) {
     final SomeService service = locator.select(SomeService.class);
     // use SomeService instance...
   }
 }
 

Method Detail

select

<T> InstanceProvider<T> select(Class<T> instanceType,
                               Annotation... qualifiers)

Obtains a child Instance for the given required type and additional required qualifiers.

Parameters:

instanceType - The type (contract) of the service to retrieve

qualifiers - Additional qualifiers that constrain which implementation to match

Returns:

InstanceProvider for the specified type and qualifiers. This value is never null.