8345339: JFR: Missing javadoc for RecordingStream::onMetadata

Reviewed-by: nbenalla, liach

src/jdk.jfr/share/classes/jdk/jfr/consumer/RecordingStream.java

@@ -455,6 +455,27 @@ public void awaitTermination() throws InterruptedException {
         directoryStream.awaitTermination();
     }
 
+    /**
+     * Registers an action to perform when new metadata arrives in the stream.
+     *
+     * The event type of an event always arrives sometime before the actual event.
+     * The action must be registered before the stream is started.
+     * <p>
+     * The following example shows how to listen to new event types, register
+     * an action if the event type name matches a regular expression and increase a
+     * counter if a matching event is found. A benefit of using an action per
+     * event type, instead of the generic {@link #onEvent(Consumer)} method,
+     * is that a stream implementation can avoid reading events that are of no
+     * interest.
+     *
+     * {@snippet class = "Snippets" region = "RecordingStreamMetadata"}
+     *
+     * @param action to perform, not {@code null}
+     *
+     * @throws IllegalStateException if an action is added after the stream has
+     *                               started
+     * @since 16
+     */
     @Override
     public void onMetadata(Consumer<MetadataEvent> action) {
         directoryStream.onMetadata(action);

src/jdk.jfr/share/classes/jdk/jfr/consumer/snippet-files/Snippets.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2022, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -109,6 +109,27 @@ public static void main(String... args) throws IOException {
         // @end
     }
 
+    class RecordingStreamMetadata {
+        // @start region="RecordingStreamMetadata"
+        static long count = 0;
+        public static void main(String... args) throws Exception {
+            String regExp = args[0];
+            var pr = Pattern.compile(regExp).asMatchPredicate();
+            Configuration c = Configuration.getConfiguration("default");
+            try (var s = new RecordingStream(c)) {
+                s.setOrdered(false);
+                s.onMetadata(metadata -> metadata.getAddedEventTypes()
+                 .stream().map(EventType::getName).filter(pr)
+                 .forEach(eventName -> s.onEvent(eventName, event -> count++)));
+                s.startAsync();
+                System.out.println("Running recording for 5 s. Please wait.");
+                s.awaitTermination(Duration.ofSeconds(5));
+                System.out.println(count + " events matches " + regExp);
+            }
+        }
+        // @end
+    }
+
     void RecordingFileOverview() throws Exception {
         // @start region="RecordingFileOverview"
         try (RecordingFile recordingFile = new RecordingFile(Paths.get("recording.jfr"))) {