OpenJDK 27 · jdk.jfr.ValueDescriptor · APIdia, the JavaDoc alternative

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());
        }
    }
}

Modifier and Type	Field and Description
private final AnnotationConstruct	annotationConstruct
private final boolean	constantPool
private String	contentType
private final boolean	isArray
private final String	javaFieldName
private String	label
private final String	name
private final Type	type
private static final String	UNKNOWN

Constructor Summary

Access	Constructor and Description
pack-priv	ValueDescriptor(Type type, String name, List<AnnotationElement> annotations, int dimension, boolean constantPool, String fieldName)
public	ValueDescriptor(Class<?> the type, not `null` type, String the name, not `null` name) Constructs a value descriptor, useful for dynamically creating event types and annotations.
public	ValueDescriptor(Class<?> the type, not `null` type, String the name, not `null` name, List<AnnotationElement> the annotations on the value descriptors, not `null` annotations) Constructs a value descriptor, useful for dynamically creating event types and annotations.
pack-priv	ValueDescriptor(Class<?> type, String name, List<AnnotationElement> annotations, boolean allowArray)

Method Summary

Modifier and Type	Method and Description
public < the type of the annotation to query for and return if present A extends Annotation> A	Returns: this element's annotation for the specified annotation type if directly present, else `null` getAnnotation(Class<A> the Class object that corresponds to the annotation type, not `null` 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.
public List<AnnotationElement>	Returns: a list of annotations, not `null` getAnnotationElements() Returns an immutable list of annotation elements for this value descriptor.
public String	Returns: the content type, or `null` if doesn't exist getContentType() Returns a textual identifier that specifies how a value represented by this `ValueDescriptor` is interpreted or formatted.
public String	Returns: the description, or `null` if doesn't exist getDescription() Returns a sentence describing the value (for example, `"Maximum throughput in the transaction system.`
public List<ValueDescriptor>	Returns: a list of value descriptors, not `null` getFields() Returns an immutable list of value descriptors if the type is complex, else an empty list.
pack-priv String	getJavaFieldName()
public String	Returns: a human-readable name, or `null` if doesn't exist getLabel() Returns a human-readable name that describes the value (for example, `"Maximum Throughput"`).
public String	Returns: the name, not `null` getName() Returns the name of the value (for example, `"maxThroughput"`).
pack-priv Type	getType()
public long	Returns: the type ID, not negative getTypeId() Returns a unique ID for the type in the Java virtual Machine (JVM).
public String	Returns: the type name, not `null` getTypeName() Returns the fully qualified class name of the type that is associated with this value descriptor.
public boolean	Returns: `true` if it is an array type, `false` otherwise isArray() Returns if this value descriptor is an array type.
pack-priv boolean	isConstantPool()
pack-priv boolean	isUnsigned()
pack-priv void	setAnnotations(List<AnnotationElement> anno)

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

annotationConstruct	back to summary
private final AnnotationConstruct annotationConstruct

constantPool	back to summary
private final boolean constantPool

contentType	back to summary
private String contentType

isArray	back to summary
private final boolean isArray

javaFieldName	back to summary
private final String javaFieldName

label	back to summary
private String label

name	back to summary
private final String name

type	back to summary
private final Type type

UNKNOWN	back to summary
private static final String UNKNOWN

Constructor Detail

ValueDescriptor	back to summary
pack-priv ValueDescriptor(Type type, String name, List<AnnotationElement> annotations, int dimension, boolean constantPool, String fieldName)

ValueDescriptor back to summary

ValueDescriptor	back to summary
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:Class<?> the type, not `null` name:String the name, not `null` Exceptions IllegalArgumentException: if the name is not a valid Java identifier

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:Class<?>: the type, not null
name:String: the name, not null

Exceptions

IllegalArgumentException:: if the name is not a valid Java identifier

ValueDescriptor back to summary

ValueDescriptor	back to summary
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:Class<?> the type, not `null` name:String the name, not `null` annotations:List<AnnotationElement> the annotations on the value descriptors, not `null` Exceptions IllegalArgumentException: if the name is not a valid Java identifier

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:Class<?>: the type, not null
name:String: the name, not null
annotations:List<AnnotationElement>: the annotations on the value descriptors, not null

Exceptions

IllegalArgumentException:: if the name is not a valid Java identifier

ValueDescriptor	back to summary
pack-priv ValueDescriptor(Class<?> type, String name, List<AnnotationElement> annotations, boolean allowArray)

Method Detail

getAnnotation back to summary

getAnnotation	back to summary
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. Parameters <A> the type of the annotation to query for and return if present annotationType:Class<A> the Class object that corresponds to the annotation type, not `null` Returns:A this element's annotation for the specified annotation type if directly present, else `null`

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.

Parameters

<A>: the type of the annotation to query for and return if present
annotationType:Class<A>: the Class object that corresponds to the annotation type, not null

Returns:A

this element's annotation for the specified annotation type if directly present, else null

getAnnotationElements back to summary

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

public List<AnnotationElement> getAnnotationElements()

Returns an immutable list of annotation elements for this value descriptor.

Returns:List<AnnotationElement>: a list of annotations, not null

getContentType back to summary

getContentType	back to summary
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:String the content type, or `null` if doesn't exist See Also `ContentType`

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

getDescription back to summary

getDescription	back to summary
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:String the description, or `null` if doesn't exist

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:String: the description, or null if doesn't exist

getFields back to summary

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

public List<ValueDescriptor> getFields()

Returns an immutable list of value descriptors if the type is complex, else an empty list.

Returns:List<ValueDescriptor>: a list of value descriptors, not null

getJavaFieldName	back to summary
pack-priv String getJavaFieldName()

getLabel back to summary

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

public String getLabel()

Returns a human-readable name that describes the value (for example, "Maximum Throughput").

Returns:String: a human-readable name, or null if doesn't exist

getName back to summary

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

public String getName()

Returns the name of the value (for example, "maxThroughput").

Returns:String: the name, not null

getType	back to summary
pack-priv Type getType()

getTypeId	back to summary
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:long the type ID, not negative

getTypeId

back to summary

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:long: the type ID, not negative

getTypeName back to summary

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

public String getTypeName()

Returns the fully qualified class name of the type that is associated with this value descriptor.

Returns:String: the type name, not null
See Also: ValueDescriptor#getTypeId()

isArray back to summary

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

public boolean isArray()

Returns if this value descriptor is an array type.

Returns:boolean: true if it is an array type, false otherwise

isConstantPool	back to summary
pack-priv boolean isConstantPool()

isUnsigned	back to summary
pack-priv boolean isUnsigned()

setAnnotations	back to summary
pack-priv void setAnnotations(List<AnnotationElement> anno)

public final Class ValueDescriptor

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail