org.apache.pulsar.shade.javax.inject.Scope Maven / Gradle / Ivy
/*
* Copyright (C) 2009 The JSR-330 Expert Group
*
* 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
*
* http://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 org.apache.pulsar.shade.javax.inject;
import java.lang.annotation.Target;
import java.lang.annotation.Retention;
import java.lang.annotation.Documented;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
/**
* Identifies scope annotations. A scope annotation applies to a class
* containing an injectable constructor and governs how the injector reuses
* instances of the type. By default, if no scope annotation is present, the
* injector creates an instance (by injecting the type's constructor), uses
* the instance for one injection, and then forgets it. If a scope annotation
* is present, the injector may retain the instance for possible reuse in a
* later injection. If multiple threads can access a scoped instance, its
* implementation should be thread safe. The implementation of the scope
* itself is left up to the injector.
*
* In the following example, the scope annotation {@code @Singleton} ensures
* that we only have one Log instance:
*
*
* @Singleton
* class Log {
* void log(String message) { ... }
* }
*
* The injector generates an error if it encounters more than one scope
* annotation on the same class or a scope annotation it doesn't support.
*
*
A scope annotation:
*
* - is annotated with {@code @Scope}, {@code @Retention(RUNTIME)},
* and typically {@code @Documented}.
* - should not have attributes.
* - is typically not {@code @Inherited}, so scoping is orthogonal to
* implementation inheritance.
* - may have restricted usage if annotated with {@code @Target}. While
* this specification covers applying scopes to classes only, some
* injector configurations might use scope annotations
* in other places (on factory method results for example).
*
*
* For example:
*
*
* @java.lang.annotation.Documented
* @java.lang.annotation.Retention(RUNTIME)
* @org.apache.pulsar.shade.javax.inject.Scope
* public @interface RequestScoped {}
*
* Annotating scope annotations with {@code @Scope} helps the injector
* detect the case where a programmer used the scope annotation on a class but
* forgot to configure the scope in the injector. A conservative injector
* would generate an error rather than not apply a scope.
*
* @see javax.inject.Singleton @Singleton
*/
@Target(ANNOTATION_TYPE)
@Retention(RUNTIME)
@Documented
public @interface Scope {}