Module jdk.jfr
Package jdk.jfr

Class ValueDescriptor

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

    • 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