Package jdk.jfr.consumer

In the following example, the program prints a histogram of all method samples in a recording.

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

     RecordingFile.readAllEvents(Path.of(args[0])).stream()
         .filter(e -> e.getEventType().getName().equals("jdk.ExecutionSample"))
         .map(e -> e.getStackTrace())
         .filter(s -> s != null)
         .map(s -> s.getFrames().get(0))
         .filter(f -> f.isJavaFrame())
         .map(f -> f.getMethod())
         .collect(
             Collectors.groupingBy(m -> m.getType().getName() + "." + m.getName() + " " + m.getDescriptor(),
             Collectors.counting()))
         .entrySet()
         .stream()
         .sorted((a, b) -> b.getValue().compareTo(a.getValue()))
         .forEach(e -> System.out.printf("%8d %s\n", e.getValue(), e.getKey()));
     }
 

Null-handling

All methods define whether they accept or return null in the Javadoc. Typically this is expressed as "not null". If a null parameter is used where it is not allowed, a java.lang.NullPointerException is thrown. If a null parameters is passed to a method that throws other exceptions, such as java.io.IOException, the java.lang.NullPointerException takes precedence, unless the Javadoc for the method explicitly states how null is handled, i.e. by throwing java.lang.IllegalArgumentException.