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| <h2 title="Annotation Type Scope" class="title">Annotation Type Scope</h2> |
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| <pre>@Target(value=ANNOTATION_TYPE) |
| @Retention(value=RUNTIME) |
| @Documented |
| public @interface <span class="memberNameLabel">Scope</span></pre> |
| <div class="block">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. |
| |
| <p>In the following example, the scope annotation <code>@Singleton</code> ensures |
| that we only have one Log instance: |
| |
| <pre> |
| @Singleton |
| class Log { |
| void log(String message) { ... } |
| }</pre> |
| |
| <p>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. |
| |
| <p>A scope annotation: |
| <ul> |
| <li>is annotated with <code>@Scope</code>, <code>@Retention(RUNTIME)</code>, |
| and typically <code>@Documented</code>.</li> |
| <li>should not have attributes.</li> |
| <li>is typically not <code>@Inherited</code>, so scoping is orthogonal to |
| implementation inheritance.</li> |
| <li>may have restricted usage if annotated with <code>@Target</code>. 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).</li> |
| </ul> |
| |
| <p>For example: |
| |
| <pre> |
| @java.lang.annotation.Documented |
| @java.lang.annotation.Retention(RUNTIME) |
| @jakarta.inject.Scope |
| public @interface RequestScoped {}</pre> |
| |
| <p>Annotating scope annotations with <code>@Scope</code> 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.</div> |
| <dl> |
| <dt><span class="seeLabel">See Also:</span></dt> |
| <dd><a href="../../jakarta/inject/Singleton.html" title="annotation in jakarta.inject"><code>@Singleton</code></a></dd> |
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