@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:
- a Standard MBean or MXBean interface;
- a method in such an interface;
- 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);
- a public constructor in the class that implements a Standard MBean or MXBean;
- a parameter in such a constructor.
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 |
- Since:
- 1.6