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public interface: Descriptor [javadoc | source]

All Implemented Interfaces:
    Cloneable, Serializable

All Known Implementing Classes:
    ImmutableDescriptor, DescriptorSupport, javax$management$Descriptor

Additional metadata for a JMX element. A {@code Descriptor} is associated with a MBeanInfo , MBeanAttributeInfo , etc. It consists of a collection of fields. A field is a name and an associated value.

Field names are not case-sensitive. The names {@code descriptorType}, {@code descriptortype}, and {@code DESCRIPTORTYPE} are all equivalent. However, the case that was used when the field was first set is preserved in the result of the #getFields and #getFieldNames methods.

Not all field names and values are predefined. New fields can be defined and added by any program.

A descriptor can be mutable or immutable. An immutable descriptor, once created, never changes. The Descriptor methods that could modify the contents of the descriptor will throw an exception for an immutable descriptor. Immutable descriptors are usually instances of ImmutableDescriptor or a subclass. Mutable descriptors are usually instances of javax.management.modelmbean.DescriptorSupport or a subclass.

Certain fields are used by the JMX implementation. This means either that the presence of the field may change the behavior of the JMX API or that the field may be set in descriptors returned by the JMX API. These fields appear in italics in the table below, and each one has a corresponding constant in the JMX class. For example, the field {@code defaultValue} is represented by the constant JMX#DEFAULT_VALUE_FIELD .

Certain other fields have conventional meanings described in the table below but they are not required to be understood or set by the JMX implementation.

Field names defined by the JMX specification in this and all future versions will never contain a period (.). Users can safely create their own fields by including a period in the name and be sure that these names will not collide with any future version of the JMX API. It is recommended to follow the Java package naming convention to avoid collisions between field names from different origins. For example, a field created by {@code example.com} might have the name {@code com.example.interestLevel}.

Note that the values in the {@code defaultValue}, {@code legalValues}, {@code maxValue}, and {@code minValue} fields should be consistent with the type returned by the {@code getType()} method for the associated {@code MBeanAttributeInfo} or {@code MBeanParameterInfo}. For MXBeans, this means that they should be of the mapped Java type, called opendata(J) in the MXBean type mapping rules.

NameTypeUsed inMeaning
defaultValueObject MBeanAttributeInfo
Default value for an attribute or parameter. See javax.management.openmbean .
deprecatedStringAny An indication that this element of the information model is no longer recommended for use. A set of MBeans defined by an application is collectively called an information model. The convention is for the value of this field to contain a string that is the version of the model in which the element was first deprecated, followed by a space, followed by an explanation of the deprecation, for example {@code "1.3 Replaced by the Capacity attribute"}.
StringAny The base name for the ResourceBundle in which the key given in the {@code descriptionResourceKey} field can be found, for example {@code "com.example.myapp.MBeanResources"}. The meaning of this field is defined by this specification but the field is not set or used by the JMX API itself.
descriptionResourceKey StringAny A resource key for the description of this element. In conjunction with the {@code descriptionResourceBundleBaseName}, this can be used to find a localized version of the description. The meaning of this field is defined by this specification but the field is not set or used by the JMX API itself.
enabledString MBeanAttributeInfo
The string {@code "true"} or {@code "false"} according as this item is enabled. When an attribute or operation is not enabled, it exists but cannot currently be accessed. A user interface might present it as a greyed-out item. For example, an attribute might only be meaningful after the {@code start()} method of an MBean has been called, and is otherwise disabled. Likewise, a notification might be disabled if it cannot currently be emitted but could be in other circumstances.
exceptionsString[] MBeanAttributeInfo, MBeanConstructorInfo, MBeanOperationInfo The class names of the exceptions that can be thrown when invoking a constructor or operation, or getting an attribute. The meaning of this field is defined by this specification but the field is not set or used by the JMX API itself. Exceptions thrown when setting an attribute are specified by the field {@code setExceptions}.
immutableInfoString MBeanInfo The string {@code "true"} or {@code "false"} according as this MBean's MBeanInfo is immutable. When this field is true, the MBeanInfo for the given MBean is guaranteed not to change over the lifetime of the MBean. Hence, a client can read it once and cache the read value. When this field is false or absent, there is no such guarantee, although that does not mean that the MBeanInfo will necessarily change. See also the {@code "jmx.mbean.info.changed"} notification.
MBeanInfo The time in milli-seconds that the MBeanInfo can reasonably be expected to be unchanged. The value can be a {@code Long} or a decimal string. This provides a hint from a DynamicMBean or any MBean that does not define {@code immutableInfo} as {@code true} that the MBeanInfo is not likely to change within this period and therefore can be cached. When this field is missing or has the value zero, it is not recommended to cache the MBeanInfo unless it has the {@code immutableInfo} set to {@code true} or it has {@code "jmx.mbean.info.changed"} in its MBeanNotificationInfo array.
interfaceClassName StringMBeanInfo The Java interface name for a Standard MBean or MXBean, as returned by Class#getName() . A Standard MBean or MXBean registered directly in the MBean Server or created using the StandardMBean class will have this field in its MBeanInfo Descriptor.
legalValues {@literal Set}MBeanAttributeInfo
Legal values for an attribute or parameter. See javax.management.openmbean .
locale StringAny The {@linkplain Locale locale} of the description in this {@code MBeanInfo}, {@code MBeanAttributeInfo}, etc, as returned by Locale#toString() .
maxValueObject MBeanAttributeInfo
Maximum legal value for an attribute or parameter. See javax.management.openmbean .
metricTypeString MBeanAttributeInfo
The type of a metric, one of the strings "counter" or "gauge". A metric is a measurement exported by an MBean, usually an attribute but sometimes the result of an operation. A metric that is a counter has a value that never decreases except by being reset to a starting value. Counter metrics are almost always non-negative integers. An example might be the number of requests received. A metric that is a gauge has a numeric value that can increase or decrease. Examples might be the number of open connections or a cache hit rate or a temperature reading.
minValueObject MBeanAttributeInfo
Minimum legal value for an attribute or parameter. See javax.management.openmbean .
mxbeanString MBeanInfo The string {@code "true"} or {@code "false"} according as this MBean is an MXBean . A Standard MBean or MXBean registered directly with the MBean Server or created using the StandardMBean class will have this field in its MBeanInfo Descriptor.
openTypeOpenType MBeanAttributeInfo

The Open Type of this element. In the case of {@code MBeanAttributeInfo} and {@code MBeanParameterInfo}, this is the Open Type of the attribute or parameter. In the case of {@code MBeanOperationInfo}, it is the Open Type of the return value. This field is set in the Descriptor for all instances of OpenMBeanAttributeInfoSupport , OpenMBeanOperationInfoSupport , and OpenMBeanParameterInfoSupport . It is also set for attributes, operations, and parameters of MXBeans.

This field can be set for an {@code MBeanNotificationInfo}, in which case it indicates the Open Type that the user data will have.

originalTypeString MBeanAttributeInfo

The original Java type of this element as it appeared in the MXBean interface method that produced this {@code MBeanAttributeInfo} (etc). For example, a method
public MemoryUsage getHeapMemoryUsage();
in an MXBean interface defines an attribute called {@code HeapMemoryUsage} of type CompositeData . The {@code originalType} field in the Descriptor for this attribute will have the value {@code "java.lang.management.MemoryUsage"}.

The format of this string is described in the section Type Names of the MXBean specification.

setExceptionsString[] MBeanAttributeInfo The class names of the exceptions that can be thrown when setting an attribute. The meaning of this field is defined by this specification but the field is not set or used by the JMX API itself. Exceptions thrown when getting an attribute are specified by the field {@code exceptions}.
MBeanNotificationInfo The severity of this notification. It can be 0 to mean unknown severity or a value from 1 to 6 representing decreasing levels of severity. It can be represented as a decimal string or an {@code Integer}.
sinceStringAny The version of the information model in which this element was introduced. A set of MBeans defined by an application is collectively called an information model. The application may also define versions of this model, and use the {@code "since"} field to record the version in which an element first appeared.
unitsString MBeanAttributeInfo
The units in which an attribute, parameter, or operation return value is measured, for example {@code "bytes"} or {@code "seconds"}.

Some additional fields are defined by Model MBeans. See the information for {@code ModelMBeanInfo}, {@code ModelMBeanAttributeInfo}, {@code ModelMBeanConstructorInfo}, {@code ModelMBeanNotificationInfo}, and {@code ModelMBeanOperationInfo}, as well as the chapter "Model MBeans" of the JMX Specification. The following table summarizes these fields. Note that when the Type in this table is Number, a String that is the decimal representation of a Long can also be used.

Nothing prevents the use of these fields in MBeans that are not Model MBeans. The displayName, severity, and visibility fields are of interest outside Model MBeans, for example. But only Model MBeans have a predefined behavior for these fields.

NameTypeUsed inMeaning
classStringModelMBeanOperationInfo Class where method is defined (fully qualified).
currencyTimeLimitNumber ModelMBeanInfo
How long cached value is valid: <0 never, =0 always, >0 seconds.
defaultObjectModelMBeanAttributeInfo Default value for attribute.
descriptorTypeStringAny Type of descriptor, "mbean", "attribute", "constructor", "operation", or "notification".
displayNameStringAny Human readable name of this item.
exportStringModelMBeanInfo Name to be used to export/expose this MBean so that it is findable by other JMX Agents.
getMethodStringModelMBeanAttributeInfo Name of operation descriptor for get method.
lastUpdatedTimeStampNumber ModelMBeanAttributeInfo
When value was set.
t or T: log all notifications, f or F: log no notifications.
Fully qualified filename to log events to.
messageIDStringModelMBeanNotificationInfo Unique key for message text (to allow translation, analysis).
messageTextStringModelMBeanNotificationInfo Text of notification.
nameStringAny Name of this item.
persistFileStringModelMBeanInfo File name into which the MBean should be persisted.
persistLocationStringModelMBeanInfo The fully qualified directory name where the MBean should be persisted (if appropriate).
persistPeriodNumber ModelMBeanInfo
Frequency of persist cycle in seconds. Used when persistPolicy is "OnTimer" or "NoMoreOftenThan".
persistPolicyString ModelMBeanInfo
One of: OnUpdate|OnTimer|NoMoreOftenThan|OnUnregister|Always|Never. See the section "MBean Descriptor Fields" in the JMX specification document.
presentationStringStringAny XML formatted string to allow presentation of data.
protocolMapDescriptorModelMBeanAttributeInfo See the section "Protocol Map Support" in the JMX specification document. Mappings must be appropriate for the attribute and entries can be updated or augmented at runtime.
roleString ModelMBeanConstructorInfo
One of "constructor", "operation", "getter", or "setter".
setMethodStringModelMBeanAttributeInfo Name of operation descriptor for set method.
severityNumber ModelMBeanNotificationInfo 0-6 where 0: unknown; 1: non-recoverable; 2: critical, failure; 3: major, severe; 4: minor, marginal, error; 5: warning; 6: normal, cleared, informative
targetObjectObjectModelMBeanOperationInfo Object on which to execute this method.
targetTypeStringModelMBeanOperationInfo type of object reference for targetObject. Can be: ObjectReference | Handle | EJBHandle | IOR | RMIReference.
valueObject ModelMBeanAttributeInfo
Current (cached) value for attribute or operation.
visibilityNumberAny 1-4 where 1: always visible, 4: rarely visible.
Method from javax.management.Descriptor Summary:
clone,   equals,   getFieldNames,   getFieldValue,   getFieldValues,   getFields,   hashCode,   isValid,   removeField,   setField,   setFields
Method from javax.management.Descriptor Detail:
 public Object clone() throws RuntimeOperationsException

    Returns a descriptor which is equal to this descriptor. Changes to the returned descriptor will have no effect on this descriptor, and vice versa. If this descriptor is immutable, it may fulfill this condition by returning itself.

 public boolean equals(Object obj)

    Compares this descriptor to the given object. The objects are equal if the given object is also a Descriptor, and if the two Descriptors have the same field names (possibly differing in case) and the same associated values. The respective values for a field in the two Descriptors are equal if the following conditions hold:

    • If one value is null then the other must be too.
    • If one value is a primitive array then the other must be a primitive array of the same type with the same elements.
    • If one value is an object array then the other must be too and Arrays#deepEquals(Object[],Object[]) must return true.
    • Otherwise Object#equals(Object) must return true.
 public String[] getFieldNames()
    Returns all the field names in the descriptor.
 public Object getFieldValue(String fieldName) throws RuntimeOperationsException
    Returns the value for a specific field name, or null if no value is present for that name.
 public Object[] getFieldValues(String fieldNames)
    Returns all the field values in the descriptor as an array of Objects. The returned values are in the same order as the {@code fieldNames} String array parameter.
 public String[] getFields()
    Returns all of the fields contained in this descriptor as a string array.
 public int hashCode()

    Returns the hash code value for this descriptor. The hash code is computed as the sum of the hash codes for each field in the descriptor. The hash code of a field with name {@code n} and value {@code v} is {@code n.toLowerCase().hashCode() ^ h}. Here {@code h} is the hash code of {@code v}, computed as follows:

    • If {@code v} is null then {@code h} is 0.
    • If {@code v} is a primitive array then {@code h} is computed using the appropriate overloading of {@code java.util.Arrays.hashCode}.
    • If {@code v} is an object array then {@code h} is computed using Arrays#deepHashCode(Object[]) .
    • Otherwise {@code h} is {@code v.hashCode()}.
 public boolean isValid() throws RuntimeOperationsException
    Returns true if all of the fields have legal values given their names.
 public  void removeField(String fieldName)
    Removes a field from the descriptor.
 public  void setField(String fieldName,
    Object fieldValue) throws RuntimeOperationsException

    Sets the value for a specific field name. This will modify an existing field or add a new field.

    The field value will be validated before it is set. If it is not valid, then an exception will be thrown. The meaning of validity is dependent on the descriptor implementation.

 public  void setFields(String[] fieldNames,
    Object[] fieldValues) throws RuntimeOperationsException

    Sets all fields in the field names array to the new value with the same index in the field values array. Array sizes must match.

    The field value will be validated before it is set. If it is not valid, then an exception will be thrown. If the arrays are empty, then no change will take effect.