Java Module jdk.jfr Package jdk.jfr Class ValueDescriptor（JDK11）

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