Module jdk.jfr

Package jdk.jfr

Class ValueDescriptor

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 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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

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 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

SecurityException - if a security manager is present and the caller doesn't have FlightRecorderPermission("registerEvent")

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