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/* * @(#)DescriptorKey.java 1.5 06/05/02 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ 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} * attribute, 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"> * <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"> * <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 { String value(); }