1 /*
2 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package javax.management;
27
28 import java.lang.annotation.*;
29
30 /**
31 * <p>Meta-annotation that describes how an annotation element relates
32 * to a field in a {@link Descriptor}. This can be the Descriptor for
33 * an MBean, or for an attribute, operation, or constructor in an
34 * MBean, or for a parameter of an operation or constructor.</p>
35 *
36 * <p>Consider this annotation for example:</p>
37 *
38 * <pre>
39 * @Documented
40 * @Target(ElementType.METHOD)
41 * @Retention(RetentionPolicy.RUNTIME)
42 * public @interface Units {
43 * <b>@DescriptorKey("units")</b>
44 * String value();
45 * }
46 * </pre>
47 *
48 * <p>and this use of the annotation:</p>
49 *
50 * <pre>
51 * public interface CacheControlMBean {
52 * <b>@Units("bytes")</b>
53 * public long getCacheSize();
54 * }
55 * </pre>
56 *
57 * <p>When a Standard MBean is made from the {@code CacheControlMBean},
58 * the usual rules mean that it will have an attribute called
59 * {@code CacheSize} of type {@code long}. The {@code @Units}
60 * annotation, given the above definition, will ensure that the
61 * {@link MBeanAttributeInfo} for this attribute will have a
62 * {@code Descriptor} that has a field called {@code units} with
63 * corresponding value {@code bytes}.</p>
64 *
65 * <p>Similarly, if the annotation looks like this:</p>
66 *
67 * <pre>
68 * @Documented
69 * @Target(ElementType.METHOD)
70 * @Retention(RetentionPolicy.RUNTIME)
71 * public @interface Units {
72 * <b>@DescriptorKey("units")</b>
73 * String value();
74 *
75 * <b>@DescriptorKey("descriptionResourceKey")</b>
76 * String resourceKey() default "";
77 *
78 * <b>@DescriptorKey("descriptionResourceBundleBaseName")</b>
79 * String resourceBundleBaseName() default "";
80 * }
81 * </pre>
82 *
83 * <p>and it is used like this:</p>
84 *
85 * <pre>
86 * public interface CacheControlMBean {
87 * <b>@Units("bytes",
88 * resourceKey="bytes.key",
89 * resourceBundleBaseName="com.example.foo.MBeanResources")</b>
90 * public long getCacheSize();
91 * }
92 * </pre>
93 *
94 * <p>then the resulting {@code Descriptor} will contain the following
95 * fields:</p>
96 *
97 * <table border="2" summary="Descriptor Fields">
98 * <tr><th>Name</th><th>Value</th></tr>
99 * <tr><td>units</td><td>"bytes"</td></tr>
100 * <tr><td>descriptionResourceKey</td><td>"bytes.key"</td></tr>
101 * <tr><td>descriptionResourceBundleBaseName</td>
102 * <td>"com.example.foo.MBeanResources"</td></tr>
103 * </table>
104 *
105 * <p>An annotation such as {@code @Units} can be applied to:</p>
106 *
107 * <ul>
108 * <li>a Standard MBean or MXBean interface;
109 * <li>a method in such an interface;
110 * <li>a parameter of a method in a Standard MBean or MXBean interface
111 * when that method is an operation (not a getter or setter for an attribute);
112 * <li>a public constructor in the class that implements a Standard MBean
113 * or MXBean;
114 * <li>a parameter in such a constructor.
115 * </ul>
116 *
117 * <p>Other uses of the annotation are ignored.</p>
118 *
119 * <p>Interface annotations are checked only on the exact interface
120 * that defines the management interface of a Standard MBean or an
121 * MXBean, not on its parent interfaces. Method annotations are
122 * checked only in the most specific interface in which the method
123 * appears; in other words, if a child interface overrides a method
124 * from a parent interface, only {@code @DescriptorKey} annotations in
125 * the method in the child interface are considered.
126 *
127 * <p>The Descriptor fields contributed in this way by different
128 * annotations on the same program element must be consistent. That
129 * is, two different annotations, or two members of the same
130 * annotation, must not define a different value for the same
131 * Descriptor field. Fields from annotations on a getter method must
132 * also be consistent with fields from annotations on the
133 * corresponding setter method.</p>
134 *
135 * <p>The Descriptor resulting from these annotations will be merged
136 * with any Descriptor fields provided by the implementation, such as
137 * the <a href="Descriptor.html#immutableInfo">{@code
138 * immutableInfo}</a> field for an MBean. The fields from the annotations
139 * must be consistent with these fields provided by the implementation.</p>
140 *
141 * <p>An annotation element to be converted into a descriptor field
142 * can be of any type allowed by the Java language, except an annotation
143 * or an array of annotations. The value of the field is derived from
144 * the value of the annotation element as follows:</p>
145 *
146 * <table border="2" summary="Descriptor Field Types">
147 * <tr><th>Annotation element</th><th>Descriptor field</th></tr>
148 * <tr><td>Primitive value ({@code 5}, {@code false}, etc)</td>
149 * <td>Wrapped value ({@code Integer.valueOf(5)},
150 * {@code Boolean.FALSE}, etc)</td></tr>
151 * <tr><td>Class constant (e.g. {@code Thread.class})</td>
152 * <td>Class name from {@link Class#getName()}
153 * (e.g. {@code "java.lang.Thread"})</td></tr>
154 * <tr><td>Enum constant (e.g. {@link ElementType#FIELD})</td>
155 * <td>Constant name from {@link Enum#name()}
156 * (e.g. {@code "FIELD"})</td></tr>
157 * <tr><td>Array of class constants or enum constants</td>
158 * <td>String array derived by applying these rules to each
159 * element</td></tr>
160 * <tr><td>Value of any other type<br>
161 * ({@code String}, {@code String[]}, {@code int[]}, etc)</td>
162 * <td>The same value</td></tr>
163 * </table>
164 *
165 * @since 1.6
166 */
167 @Documented
168 @Retention(RetentionPolicy.RUNTIME)
169 @Target(ElementType.METHOD)
170 public @interface DescriptorKey {
171 String value();
172 }