Class FlightRecorder

java.lang.Object
jdk.jfr.FlightRecorder
public final class FlightRecorder extends Object
Class for accessing, controlling, and managing Flight Recorder.

This class provides the methods necessary for creating, starting, stopping, and destroying recordings.

Since:
9

  • Method Details

    • getRecordings

      public List<Recording> getRecordings()
      Returns an immutable list of the available recordings.

      A recording becomes available when it is created. It becomes unavailable when it is in the CLOSED state, typically after a call to Recording.close().

      Returns:
      a list of recordings, not null

    • takeSnapshot

      public Recording takeSnapshot()
      Creates a snapshot of all available recorded data.

      A snapshot is a synthesized recording in a STOPPED state. If no data is available, a recording with size 0 is returned.

      A snapshot provides stable access to data for later operations (for example, operations to change the interval or to reduce the data size).

      The following example shows how to create a snapshot and write a subset of the data to a file. 

      try (Recording snapshot = FlightRecorder.getFlightRecorder().takeSnapshot()) {
    if (snapshot.getSize() > 0) {
        snapshot.setMaxSize(100_000_000);
        snapshot.setMaxAge(Duration.ofMinutes(5));
        snapshot.dump(Paths.get("snapshot.jfr"));
    }
}
      The caller must close the recording when access to the data is no longer needed.
      Returns:
      a snapshot of all available recording data, not null

    • register

      public static void register(Class<? extends Event> eventClass)
      Registers an event class.

      If the event class is already registered, then the invocation of this method is ignored.

      Parameters:
      eventClass - the event class to register, not null
      Throws:
      IllegalArgumentException - if class is abstract or not a subclass of Event

    • unregister

      public static void unregister(Class<? extends Event> eventClass)
      Unregisters an event class.

      If the event class is not registered, then the invocation of this method is ignored.

      Parameters:
      eventClass - the event class to unregistered, not null
      Throws:
      IllegalArgumentException - if a class is abstract or not a subclass of Event

    • getFlightRecorder

      public static FlightRecorder getFlightRecorder() throws IllegalStateException
      Returns the Flight Recorder for the platform.
      Returns:
      a Flight Recorder instance, not null
      Throws:
      IllegalStateException - if Flight Recorder can't be created (for example, if the Java Virtual Machine (JVM) lacks Flight Recorder support, or if the file repository can't be created or accessed)

    • addPeriodicEvent

      public static void addPeriodicEvent(Class<? extends Event> eventClass, Runnable hook)
      Adds a hook for a periodic event.

      The implementation of the hook should return as soon as possible, to avoid blocking other Flight Recorder operations. The hook should emit one or more events of the specified type. When a hook is added, the interval at which the call is invoked is configurable using the "period" setting.

      Parameters:
      eventClass - the class that the hook should run for, not null
      hook - the hook, not null
      Throws:
      IllegalArgumentException - if a class is not a subclass of Event, is abstract, or the hook is already added
      IllegalStateException - if the event class has the Registered(false) annotation and is not registered manually

    • removePeriodicEvent

      public static boolean removePeriodicEvent(Runnable hook)
      Removes a hook for a periodic event.
      Parameters:
      hook - the hook to remove, not null
      Returns:
      true if hook is removed, false otherwise

    • getEventTypes

      public List<EventType> getEventTypes()
      Returns an immutable list that contains all currently registered events.

      By default, events are registered when they are first used, typically when an event object is allocated. To ensure an event is visible early, registration can be triggered by invoking the register(Class) method.

      Returns:
      list of events, not null

    • addListener

      public static void addListener(FlightRecorderListener changeListener)
      Adds a recorder listener and captures the AccessControlContext to use when invoking the listener.

      If Flight Recorder is already initialized when the listener is added, then the method FlightRecorderListener.recorderInitialized(FlightRecorder) method is invoked before returning from this method.

      Parameters:
      changeListener - the listener to add, not null

    • removeListener

      public static boolean removeListener(FlightRecorderListener changeListener)
      Removes a recorder listener.

      If the same listener is added multiple times, only one instance is removed.

      Parameters:
      changeListener - listener to remove, not null
      Returns:
      true, if the listener could be removed, false otherwise

    • isAvailable

      public static boolean isAvailable()
      Returns true if the Java Virtual Machine (JVM) has Flight Recorder capabilities.

      This method can quickly check whether Flight Recorder can be initialized, without actually doing the initialization work. The value may change during runtime and it is not safe to cache it.

      Returns:
      true, if Flight Recorder is available, false otherwise
      See Also:

    • isInitialized

      public static boolean isInitialized()
      Returns true if Flight Recorder is initialized.
      Returns:
      true, if Flight Recorder is initialized, false otherwise
      See Also: