Provides the open data types and Open MBean descriptor classes.
An Open MBean is an MBean where the types of attributes
and of operation parameters and return values are built using a
small set of predefined Java classes. Open MBeans facilitate
operation with remote management programs that do not necessarily
have access to application-specific types, including non-Java
programs.
Every MBean has an MBeanInfo
with information about the MBean itself, and its
attributes, operations, constructors, and notifications. In an
Open MBean, this MBeanInfo
implements the OpenMBeanInfo
interface, usually by being an instance of OpenMBeanInfoSupport
.
The attribute information returned by MBeanInfo.getAttributes
for an Open MBean is an array of
objects implementing OpenMBeanAttributeInfo
, usually instances of OpenMBeanAttributeInfoSupport
. In addition to the usual
information about attributes, an
OpenMBeanAttributeInfo
specifies the OpenType
of the attribute.
The possible OpenType
values are predefined, which
is what ensures that remote managers will understand them.
Similar remarks apply to the parameter types of operations and
constructors, and to the return types of operations.
There is a distinction between an attribute's Java language
type, as returned by getType()
, and
its OpenType
, as returned by getOpenType()
. For example, if the Java language type is
java.lang.String
, the OpenType
will be
SimpleType.String
. If the Java language type is CompositeData
, the
OpenType
will be a CompositeType
that
describes the items in the CompositeData
instances
for the attribute.
In Open MBeans, attributes and parameters can have default values
and/or constraints associated with them in the OpenMBeanAttributeInfo
or OpenMBeanParameterInfo
.
There are two ways to specify these constraints. Either the
values are directly specified as parameters to one of the
constructors of OpenMBeanAttributeInfoSupport
or
OpenMBeanParameterInfoSupport
, for example
OpenMBeanParameterInfoSupport.OpenMBeanParameterInfoSupport(
String, String, OpenType, Object, Object[])
; or the values are
specified in a Descriptor
given
as a parameter to one of the constructors.
When a Descriptor
is used, the fields of interest are
these:
For defaultValue
, minValue
, and maxValue
, the associated value must either be of the Java type
corresponding to openType
, or be a string that can be
converted into that type. The conversion uses the static method
valueOf(String)
if it finds one; otherwise a constructor
with a single String
parameter if it finds one; otherwise
it fails.
For legalValues
, the associated value must be either
an array or a Set
, and the elements of the array or set
must be convertible as described for defaultValue
etc.
The following conditions must be met for these fields:
- the values must be of the appropriate type, or be strings
that can be converted to the appropriate type as explained
above;
- if
legalValues
is present then neither minValue
nor maxValue
must be present;
- if
defaultValue
is present then it must satisfy the
constraints defined by legalValues
, minValue
, or
maxValue
when any of these is also present;
- if
minValue
and maxValue
are both present
then minValue
must not be greater than maxValue
.