/* * Copyright (c) 2005, 2008, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * 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. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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> * &#64;Documented * &#64;Target(ElementType.METHOD) * &#64;Retention(RetentionPolicy.RUNTIME) * public &#64;interface Units { *     <b>&#64;DescriptorKey("units")</b> *     String value(); * } * </pre> * * <p>and this use of the annotation:</p> * * <pre> * public interface CacheControlMBean { *     <b>&#64;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> * &#64;Documented * &#64;Target(ElementType.METHOD) * &#64;Retention(RetentionPolicy.RUNTIME) * public &#64;interface Units { *     <b>&#64;DescriptorKey("units")</b> *     String value(); * *     <b>&#64;DescriptorKey("descriptionResourceKey")</b> *     String resourceKey() default ""; * *     <b>&#64;DescriptorKey("descriptionResourceBundleBaseName")</b> *     String resourceBundleBaseName() default ""; * } * </pre> * * <p>and it is used like this:</p> * * <pre> * public interface CacheControlMBean { *     <b>&#64;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();}