java.lang.Object

jdk.jfr.ValueDescriptor

public final class ValueDescriptor extends Object

Describes the event fields and annotation elements.

The following example shows how the ValueDescriptor class can be used to list field information of all types.

void printTypes() {
    Map<String, List<ValueDescriptor>> typeMap = new LinkedHashMap<>();
    for (EventType eventType : FlightRecorder.getFlightRecorder().getEventTypes()) {
        findTypes(typeMap, eventType.getName(), eventType.getFields());
    }
    for (String type : typeMap.keySet()) {
        System.out.println("Type: " + type);
        for (ValueDescriptor field : typeMap.get(type)) {
            System.out.println(" Field: " + field.getName());
            String arrayBrackets = field.isArray() ? "[]" : "";
            System.out.println("  Type: " + field.getTypeName() + arrayBrackets);
            if (field.getLabel() != null) {
                System.out.println("  Label: " + field.getLabel());
            }
            if (field.getDescription() != null) {
                System.out.println("  Description: " + field.getDescription());
            }
            if (field.getContentType() != null) {
                System.out.println("  Content Types: " + field.getContentType());
            }
        }
        System.out.println();
    }
}

void findTypes(Map<String, List<ValueDescriptor>> typeMap, String typeName, List<ValueDescriptor> fields) {
    if (!typeMap.containsKey(typeName)) {
        typeMap.put(typeName, fields);
        for (ValueDescriptor subField : fields) {
            findTypes(typeMap, subField.getTypeName(), subField.getFields());
        }
    }
}

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.

Methods declared in class Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Modifier and Type

Method

Description

protected Object

clone()

Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.

boolean

equals(Object o)

Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.

protected void

finalize()

Deprecated, for removal: This API element is subject to removal in a future version.
May cause performance issues, deadlocks and hangs.

final Class<? extends Object>

getClass()

Answers the unique instance of java.lang.Class which represents the class of the receiver.

int

hashCode()

Answers an integer hash code for the receiver.

final void

notify()

Causes one thread which is waiting on the receiver to be made ready to run.

final void

notifyAll()

Causes all threads which are waiting on the receiver to be made ready to run.

String

toString()

Answers a string containing a concise, human-readable description of the receiver.

final void

wait()

Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).

final void

wait(long time)

Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

final void

wait(long time, int frac)

Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

Constructor Details
- 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 section 3.8 and 3.9 of the Java Language Specification for more information.
  
  Parameters:
  
  type - the type, not null
  
  name - the name, not null
  
  Throws:
  
  IllegalArgumentException - if the name is not a valid Java identifier
- 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 section 3.8 and 3.9 of the 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:
  
  IllegalArgumentException - if the name is not a valid Java identifier
Method Details
- 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

Class ValueDescriptor

Constructor Summary

Method Summary

Methods declared in class Object

Constructor Details

ValueDescriptor

ValueDescriptor

Method Details

getLabel

getName

getDescription

getContentType

getTypeName

getTypeId

isArray

getAnnotation

getAnnotationElements

getFields