Java Module jdk.jfr Package jdk.jfr Class FlightRecorder（JDK11）

Method Detail

• 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 STOPPPED 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

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

• 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

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

• getFlightRecorder

  public static FlightRecorder getFlightRecorder()
                                          throws IllegalStateException,
                                                 SecurityException

  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)

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

• addPeriodicEvent

  public static void addPeriodicEvent​(Class<? extends Event> eventClass,
                                      Runnable hook)
                               throws SecurityException

  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

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

• removePeriodicEvent

  public static boolean removePeriodicEvent​(Runnable hook)
                                     throws SecurityException

  Removes a hook for a periodic event.

  Parameters:

  hook - the hook to remove, not null

  Returns:

  true if hook is removed, false otherwise

  Throws:

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

• 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

  Throws:

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

• 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

  Throws:

  SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

• 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:

  for callback when Flight Recorder is initialized

• isInitialized

  public static boolean isInitialized()

  Returns true if Flight Recorder is initialized.

  Returns:

  true, if Flight Recorder is initialized, false otherwise

  See Also:

  for callback when Flight Recorder is initialized