@Documented @Retention(RUNTIME) @Target(METHOD) public @interface DescriptorKey
Meta-annotation that describes how an annotation element relates to a field in a 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.
Consider this annotation for example:
@Documented @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface Units { @DescriptorKey("units") String value(); }
and this use of the annotation:
public interface CacheControlMBean { @Units("bytes") public long getCacheSize(); }
When a Standard MBean is made from the CacheControlMBean
, the usual rules mean that it will have an attribute called CacheSize
of type long
. The @Units
annotation, given the above definition, will ensure that the MBeanAttributeInfo
for this attribute will have a Descriptor
that has a field called units
with corresponding value bytes
.
Similarly, if the annotation looks like this:
@Documented @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface Units { @DescriptorKey("units") String value(); @DescriptorKey("descriptionResourceKey") String resourceKey() default ""; @DescriptorKey("descriptionResourceBundleBaseName") String resourceBundleBaseName() default ""; }
and it is used like this:
public interface CacheControlMBean { @Units("bytes", resourceKey="bytes.key", resourceBundleBaseName="com.example.foo.MBeanResources") public long getCacheSize(); }
then the resulting Descriptor
will contain the following fields:
Name | Value |
---|---|
units | "bytes" |
descriptionResourceKey | "bytes.key" |
descriptionResourceBundleBaseName | "com.example.foo.MBeanResources" |
An annotation such as @Units
can be applied to:
Other uses of the annotation are ignored.
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 @DescriptorKey
annotations in the method in the child interface are considered.
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.
The Descriptor resulting from these annotations will be merged with any Descriptor fields provided by the implementation, such as the
immutableInfo
field for an MBean. The fields from the annotations must be consistent with these fields provided by the implementation.
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:
Annotation element | Descriptor field |
---|---|
Primitive value (5 , false , etc) | Wrapped value (Integer.valueOf(5) , Boolean.FALSE , etc) |
Class constant (e.g. Thread.class ) | Class name from Class.getName() (e.g. "java.lang.Thread" ) |
Enum constant (e.g. ElementType.FIELD ) | Constant name from Enum.name() (e.g. "FIELD" ) |
Array of class constants or enum constants | String array derived by applying these rules to each element |
Value of any other type ( String , String[] , int[] , etc) | The same value |
Modifier and Type | Required Element | Description |
---|---|---|
String |
value |
Returns the descriptor key. |
String value
© 1993, 2023, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
https://docs.oracle.com/en/java/javase/21/docs/api/java.management/javax/management/DescriptorKey.html