Java Flight Recorder - how to extract the values of a custom event field?

Question

Java Flight Recorder is now a part of OpenJDK 11 and offers the usage of custom events. After a successful recording, I want to reuse the information within the events (especially my own custom events), but somehow I am unable to read the field content of an event. I can only see the annotations, the name and the type of the fields.

Does anybody know whether this is actually possible?

JFR has a consumer package which allows you to read information from the files. I already apply some of the functions.

What I already tried

First, I access all the fields of an event:

event.getFields();

Then I iterate over the fields and access their values in a few different ways:

a) eventField.getDescriptor();
b) eventField.getContentType();

Just looking at their names, obviously none of them would give me the content. Unfortunately I couldn't find any function that could help.

What I also tried

I also tried a very straight-forward idea: read the content in debug modus. I thought it would offer me some insight on how to programatically extract those information.

Unfortunately, JFR managed to encode their recordings in a way, that during a debug procedure, one is not able to read the information, until one programatically extracted them and has it as a local variable (example: a map).

For your information, I have been using this instruction for the custom event implementation.

Answer 1

Here is a short program that illustrates how you can get the values

public class Example {
  public static void main(String[] args) throws IOException {
  if (args.length != 1) {
    System.err.println("Must specify a recording file.");
    return;
  }

  List<RecordedEvent> events = RecordingFile.readAllEvents(Path.of(args[0]));
  for (RecordedEvent event : events) {
    EventType eventType = event.getEventType();
    String name = eventType.getName();
    Instant start = event.getStartTime();
    Instant end = event.getEndTime();
    System.out.println(name + " " + start + " - " + end);
    for (ValueDescriptor field : eventType.getFields()) {
      String fieldName = field.getName();
      Object value = event.getValue(fieldName);
      System.out.println(fieldName + " = " + value);
    }
    System.out.println();
  }
}

If you want to find example code of all aspects of JFR, you can look in the test folder in the OpenJDK project. For example, the test of a RecordedEvent