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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
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* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package javax.management;
import java.lang.annotation.*;
/**
* <p>Meta-annotation that describes how an annotation element relates
* to a field in a {@link Descriptor}. This can be the Descriptor for
* an MBean, or for an attribute, operation, or constructor in an
* MBean, or for a parameter of an operation or constructor.</p>
*
* <p>Consider this annotation for example:</p>
*
* <pre>
* @Documented
* @Target(ElementType.METHOD)
* @Retention(RetentionPolicy.RUNTIME)
* public @interface Units {
* <b>@DescriptorKey("units")</b>
* String value();
* }
* </pre>
*
* <p>and this use of the annotation:</p>
*
* <pre>
* public interface CacheControlMBean {
* <b>@Units("bytes")</b>
* public long getCacheSize();
* }
* </pre>
*
* <p>When a Standard MBean is made from the {@code CacheControlMBean},
* the usual rules mean that it will have an attribute called
* {@code CacheSize} of type {@code long}. The {@code @Units}
* annotation, given the above definition, will ensure that the
* {@link MBeanAttributeInfo} for this attribute will have a
* {@code Descriptor} that has a field called {@code units} with
* corresponding value {@code bytes}.</p>
*
* <p>Similarly, if the annotation looks like this:</p>
*
* <pre>
* @Documented
* @Target(ElementType.METHOD)
* @Retention(RetentionPolicy.RUNTIME)
* public @interface Units {
* <b>@DescriptorKey("units")</b>
* String value();
*
* <b>@DescriptorKey("descriptionResourceKey")</b>
* String resourceKey() default "";
*
* <b>@DescriptorKey("descriptionResourceBundleBaseName")</b>
* String resourceBundleBaseName() default "";
* }
* </pre>
*
* <p>and it is used like this:</p>
*
* <pre>
* public interface CacheControlMBean {
* <b>@Units("bytes",
* resourceKey="bytes.key",
* resourceBundleBaseName="com.example.foo.MBeanResources")</b>
* public long getCacheSize();
* }
* </pre>
*
* <p>then the resulting {@code Descriptor} will contain the following
* fields:</p>
*
* <table border="2" summary="Descriptor Fields">
* <tr><th>Name</th><th>Value</th></tr>
* <tr><td>units</td><td>"bytes"</td></tr>
* <tr><td>descriptionResourceKey</td><td>"bytes.key"</td></tr>
* <tr><td>descriptionResourceBundleBaseName</td>
* <td>"com.example.foo.MBeanResources"</td></tr>
* </table>
*
* <p>An annotation such as {@code @Units} can be applied to:</p>
*
* <ul>
* <li>a Standard MBean or MXBean interface;
* <li>a method in such an interface;
* <li>a parameter of a method in a Standard MBean or MXBean interface
* when that method is an operation (not a getter or setter for an attribute);
* <li>a public constructor in the class that implements a Standard MBean
* or MXBean;
* <li>a parameter in such a constructor.
* </ul>
*
* <p>Other uses of the annotation are ignored.</p>
*
* <p>Interface annotations are checked only on the exact interface
* that defines the management interface of a Standard MBean or an
* MXBean, not on its parent interfaces. Method annotations are
* checked only in the most specific interface in which the method
* appears; in other words, if a child interface overrides a method
* from a parent interface, only {@code @DescriptorKey} annotations in
* the method in the child interface are considered.
*
* <p>The Descriptor fields contributed in this way by different
* annotations on the same program element must be consistent. That
* is, two different annotations, or two members of the same
* annotation, must not define a different value for the same
* Descriptor field. Fields from annotations on a getter method must
* also be consistent with fields from annotations on the
* corresponding setter method.</p>
*
* <p>The Descriptor resulting from these annotations will be merged
* with any Descriptor fields provided by the implementation, such as
* the <a href="Descriptor.html#immutableInfo">{@code
* immutableInfo}</a> field for an MBean. The fields from the annotations
* must be consistent with these fields provided by the implementation.</p>
*
* <p>An annotation element to be converted into a descriptor field
* can be of any type allowed by the Java language, except an annotation
* or an array of annotations. The value of the field is derived from
* the value of the annotation element as follows:</p>
*
* <table border="2" summary="Descriptor Field Types">
* <tr><th>Annotation element</th><th>Descriptor field</th></tr>
* <tr><td>Primitive value ({@code 5}, {@code false}, etc)</td>
* <td>Wrapped value ({@code Integer.valueOf(5)},
* {@code Boolean.FALSE}, etc)</td></tr>
* <tr><td>Class constant (e.g. {@code Thread.class})</td>
* <td>Class name from {@link Class#getName()}
* (e.g. {@code "java.lang.Thread"})</td></tr>
* <tr><td>Enum constant (e.g. {@link ElementType#FIELD})</td>
* <td>Constant name from {@link Enum#name()}
* (e.g. {@code "FIELD"})</td></tr>
* <tr><td>Array of class constants or enum constants</td>
* <td>String array derived by applying these rules to each
* element</td></tr>
* <tr><td>Value of any other type<br>
* ({@code String}, {@code String[]}, {@code int[]}, etc)</td>
* <td>The same value</td></tr>
* </table>
*
* @since 1.6
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DescriptorKey {
/**
* Returns the descriptor key.
* @return the descriptor key
*/
String value();
}