io.micronaut.context.annotation.DefaultImplementation Maven / Gradle / Ivy
/*
* Copyright 2017-2020 original authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.micronaut.context.annotation;
import io.micronaut.core.annotation.Experimental;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
/**
* An annotation to apply to an interface to indicate which implementation
* is the default implementation.
*
* When a bean is looked up and if there are multiple possible candidates with
* no concrete {@link Primary} this annotation will impact bean selection by
* selecting the default implementation.
*
* It should be noted that {@link Primary} and {@link io.micronaut.core.order.Ordered}
* take precedence over this an annotation and a fallback to the default implementation only
* occurs if no primary candidate can be established.
*
* Note that this annotation also has an impact on bean replacement via {@link Replaces}
* to another class to allow the replacement of an implementation that isn't
* accessible due to visibility restrictions.
*
* For example:
*
*
* @DefaultImplementation(MyImpl.class)
* public interface SomeInterface {
*
* }
*
* class MyImpl implements SomeInterface {
*
* }
*
* @Replaces(SomeInterface.class)
* class OtherImpl implements SomeInterface {
*
* }
*
*
* In the above example the {@code OtherImpl} bean will replace the
* {@code MyImpl} bean because the class in the {@link Replaces} annotation
* has a default implementation.
*
* @author James Kleeh
* @since 1.2.0
*/
@Documented
@Retention(RUNTIME)
@Target(ElementType.TYPE)
@Experimental
@Inherited
public @interface DefaultImplementation {
/**
* @return The bean type that is the default implementation
*/
@AliasFor(member = "name")
Class value() default void.class;
/**
* @return The fully qualified bean type name that is the default implementation
*/
String name() default "";
}