Module jdk.jfr
Package jdk.jfr

Class ValueDescriptor

  • public final class ValueDescriptor
extends Object
    Describes the event fields and annotation elements.
    Since:
    9

    • Constructor Summary

      Constructors 
      Constructor Description
      ValueDescriptor​(Class<?> type, String name)
      Constructs a value descriptor, useful for dynamically creating event types and annotations.
      ValueDescriptor​(Class<?> type, String name, List<AnnotationElement> annotations)
      Constructs a value descriptor, useful for dynamically creating event types and annotations.

    • Method Summary

      Modifier and Type Method Description
      <A extends Annotation>
      A      		 getAnnotation​(Class<A> annotationType)
      Returns the first annotation for the specified type if an annotation element with the same name is directly present for this value descriptor, null otherwise.
      List<AnnotationElement> getAnnotationElements()
      Returns an immutable list of annotation elements for this value descriptor.
      String getContentType()
      Returns a textual identifier that specifies how a value represented by this ValueDescriptor is interpreted or formatted.
      String getDescription()
      Returns a sentence describing the value (for example, "Maximum throughput in the transaction system. Value is reset after each new batch.").
      List<ValueDescriptor> getFields()
      Returns an immutable list of value descriptors if the type is complex, else an empty list.
      String getLabel()
      Returns a human-readable name that describes the value (for example, "Maximum Throughput").
      String getName()
      Returns the name of the value (for example, "maxThroughput").
      long getTypeId()
      Returns a unique ID for the type in the Java virtual Machine (JVM).
      String getTypeName()
      Returns the fully qualified class name of the type that is associated with this value descriptor.
      boolean isArray()
      Returns if this value descriptor is an array type.

    • Constructor Detail

      • ValueDescriptor

        public ValueDescriptor​(Class<?> type,
                       String name)

        Constructs a value descriptor, useful for dynamically creating event types and annotations.

        The following types are supported:

        • byte.class
        • short.class
        • int.class
        • long.class
        • char.class
        • float.class
        • double.class
        • boolean.class
        • String.class
        • Class.class
        • Thread.class

        The name must be a valid Java identifier (for example, "maxThroughput"). See 3.8 Java Language Specification for more information.

        Parameters:
        type - the type, not null
        name - the name, not null
        Throws:
        SecurityException - if a security manager is present and the caller doesn't have FlightRecorderPermission("registerEvent")

      • ValueDescriptor

        public ValueDescriptor​(Class<?> type,
                       String name,
                       List<AnnotationElement> annotations)

        Constructs a value descriptor, useful for dynamically creating event types and annotations.

        The following types are supported:

        • byte.class
        • short.class
        • int.class
        • long.class
        • char.class
        • float.class
        • double.class
        • boolean.class
        • String.class
        • Class.class
        • Thread.class

        The name must be a valid Java identifier (for example, "maxThroughput"). See 3.8 Java Language Specification for more information.

        Parameters:
        type - the type, not null
        name - the name, not null
        annotations - the annotations on the value descriptors, not null
        Throws:
        SecurityException - if a security manager is present and the caller doesn't have FlightRecorderPermission("registerEvent")

    • Method Detail

      • getLabel

        public String getLabel()
        Returns a human-readable name that describes the value (for example, "Maximum Throughput").
        Returns:
        a human-readable name, or null if doesn't exist

      • getName

        public String getName()
        Returns the name of the value (for example, "maxThroughput").
        Returns:
        the name, not null

      • getDescription

        public String getDescription()
        Returns a sentence describing the value (for example, "Maximum throughput in the transaction system. Value is reset after each new batch.").
        Returns:
        the description, or null if doesn't exist

      • getContentType

        public String getContentType()
        Returns a textual identifier that specifies how a value represented by this ValueDescriptor is interpreted or formatted.

        For example, if the value descriptor's type is float and the event value is 0.5f, a content type of "jdk.jfr.Percentage" hints to a client that the value is a percentage and that it should be rendered as "50%".

        The JDK provides the following predefined content types:

        • jdk.jfr.Percentage
        • jdk.jfr.Timespan
        • jdk.jfr.Timestamp
        • jdk.jfr.Frequency
        • jdk.jfr.Flag
        • jdk.jfr.MemoryAddress
        • jdk.jfr.DataAmount
        • jdk.jfr.NetworkAddress

        User-defined content types can be created by using the ContentType class.

        Returns:
        the content type, or null if doesn't exist
        See Also:
        ContentType

      • getTypeName

        public String getTypeName()
        Returns the fully qualified class name of the type that is associated with this value descriptor.
        Returns:
        the type name, not null
        See Also:
        getTypeId()

      • getTypeId

        public long getTypeId()
        Returns a unique ID for the type in the Java virtual Machine (JVM). The ID might not be the same between JVM instances.
        Returns:
        the type ID, not negative

      • isArray

        public boolean isArray()
        Returns if this value descriptor is an array type.
        Returns:
        true if it is an array type, false otherwise

      • getAnnotation

        public <A extends Annotation> A getAnnotation​(Class<A> annotationType)
        Returns the first annotation for the specified type if an annotation element with the same name is directly present for this value descriptor, null otherwise.
        Type Parameters:
        A - the type of the annotation to query for and return if present
        Parameters:
        annotationType - the Class object that corresponds to the annotation type, not null
        Returns:
        this element's annotation for the specified annotation type if directly present, else null

      • getAnnotationElements

        public List<AnnotationElement> getAnnotationElements()
        Returns an immutable list of annotation elements for this value descriptor.
        Returns:
        a list of annotations, not null

      • getFields

        public List<ValueDescriptor> getFields()
        Returns an immutable list of value descriptors if the type is complex, else an empty list.
        Returns:
        a list of value descriptors, not null