Module jdk.jfr
Package jdk.jfr

Class EventFactory

  • public final class EventFactory
extends Object
    Class for defining an event at runtime.

    It's highly recommended that the event is defined at compile time, if the field layout is known, so the Java Virtual Machine (JVM) can optimize the code, possibly remove all instrumentation if Flight Recorder is inactive or if the enabled setting for this event is set to false.

    To define an event at compile time, see Event.

    The following example shows how to implement a dynamic Event class. 

     
 List<ValueDescriptor> fields = new ArrayList<>();
 List<AnnotationElement> messageAnnotations = Collections.singletonList(new AnnotationElement(Label.class, "Message"));
 fields.add(new ValueDescriptor(String.class, "message", messageAnnotations));
 List<AnnotationElement> numberAnnotations = Collections.singletonList(new AnnotationElement(Label.class, "Number"));
 fields.add(new ValueDescriptor(int.class, "number", numberAnnotations));

 String[] category = { "Example", "Getting Started" };
 List<AnnotationElement> eventAnnotations = new ArrayList<>();
 eventAnnotations.add(new AnnotationElement(Name.class, "com.example.HelloWorld"));
 eventAnnotations.add(new AnnotationElement(Label.class, "Hello World"));
 eventAnnotations.add(new AnnotationElement(Description.class, "Helps programmer getting started"));
 eventAnnotations.add(new AnnotationElement(Category.class, category));

 EventFactory f = EventFactory.create(eventAnnotations, fields);

 Event event = f.newEvent();
 event.set(0, "hello, world!");
 event.set(1, 4711);
 event.commit();
    Since:
    9

    • Method Detail

      • create

        public static EventFactory create​(List<AnnotationElement> annotationElements,
                                  List<ValueDescriptor> fields)
        Creates an EventFactory object.

        The order of the value descriptors specifies the index to use when setting event values.

        Parameters:
        annotationElements - list of annotation elements that describes the annotations on the event, not null
        fields - list of descriptors that describes the fields of the event, not null
        Returns:
        event factory, not null
        Throws:
        IllegalArgumentException - if the input is not valid. For example, input might not be valid if the field type or name is not valid in the Java language or an annotation element references a type that can't be found.
        SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")
        See Also:
        Event.set(int, Object)

      • newEvent

        public Event newEvent()
        Instantiates an event, so it can be populated with data and written to the Flight Recorder system.

        Use the Event.set(int, Object) method to set a value.

        Returns:
        an event instance, not null

      • getEventType

        public EventType getEventType()
        Returns the event type that is associated with this event factory.
        Returns:
        event type that is associated with this event factory, not null
        Throws:
        IllegalStateException - if the event factory is created with the Registered(false) annotation and the event class is not manually registered before the invocation of this method

      • register

        public void register()
        Registers an unregistered event.

        By default, the event class associated with this event factory is registered when the event factory is created, unless the event has the Registered annotation.

        A registered event class can write data to Flight Recorder and event metadata can be obtained by invoking FlightRecorder.getEventTypes().

        If the event class associated with this event factory is already registered, the call to this method is ignored.

        Throws:
        SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")
        See Also:
        Registered, FlightRecorder.register(Class)

      • unregister

        public void unregister()
        Unregisters the event that is associated with this event factory.

        A unregistered event class can't write data to Flight Recorder and event metadata can't be obtained by invoking FlightRecorder.getEventTypes().

        If the event class associated with this event factory is not already registered, the call to this method is ignored.

        Throws:
        SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")
        See Also:
        Registered, FlightRecorder.unregister(Class)