add OnStopHandler again as functional interface

Signed-off-by: Dominik Guggemos <dominik.guggemos@bosch.io>

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/OnStopHandler.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.internal.utils.metrics.instruments.timer;
+
+/**
+ * To be invoked when a Timer stops.
+ */
+@FunctionalInterface
+public interface OnStopHandler {
+
+    /**
+     * Handles the passed {@code stoppedTimer}.
+     *
+     * @param stoppedTimer the StoppedTimer to handle.
+     */
+    void handleStoppedTimer(final StoppedTimer stoppedTimer);
+}

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/StartedKamonTimer.java

@@ -34,7 +34,7 @@ final class StartedKamonTimer implements StartedTimer {
 
     private final String name;
     private final Map<String, String> tags;
-    private final List<Consumer<StoppedTimer>> onStopHandlers;
+    private final List<OnStopHandler> onStopHandlers;
     private final Map<String, StartedTimer> segments;
     private final long startNanoTime;
     private final Instant startInstant;
@@ -128,7 +128,7 @@ public StartedTimer startNewSegment(final String segmentName) {
     }
 
     @Override
-    public StartedTimer onStop(final Consumer<StoppedTimer> onStopHandler) {
+    public StartedTimer onStop(final OnStopHandler onStopHandler) {
         onStopHandlers.add(onStopHandler);
         return this;
     }
@@ -154,7 +154,7 @@ public Map<String, StartedTimer> getSegments() {
     }
 
     @Override
-    public List<Consumer<StoppedTimer>> getOnStopHandlers() {
+    public List<OnStopHandler> getOnStopHandlers() {
         return List.copyOf(onStopHandlers);
     }
 

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/StartedTimer.java

@@ -54,7 +54,14 @@ public interface StartedTimer extends Timer, TaggedMetricInstrument<StartedTimer
      *
      * @param onStopHandler the handler to invoke when this timer stops.
      */
-    StartedTimer onStop(Consumer<StoppedTimer> onStopHandler);
+    StartedTimer onStop(OnStopHandler onStopHandler);
+
+    /**
+     * Gets all on stop handlers of this timer.
+     *
+     * @return All on stop handlers of this timer.
+     */
+    List<OnStopHandler> getOnStopHandlers();
 
     /**
      * @return the instant when the timer was started.
@@ -74,11 +81,4 @@ public interface StartedTimer extends Timer, TaggedMetricInstrument<StartedTimer
      * @return Segments of this timer.
      */
     Map<String, StartedTimer> getSegments();
-
-    /**
-     * Gets all on stop handlers of this timer.
-     *
-     * @return All on stop handlers of this timer.
-     */
-    List<Consumer<StoppedTimer>> getOnStopHandlers();
 }

internal/utils/metrics/src/main/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/StoppedKamonTimer.java

@@ -52,7 +52,7 @@ private StoppedKamonTimer(final StartedTimer startedTimer) {
         final long durationNano = getElapsedNano();
         LOGGER.trace("Timer with name <{}> and segment <{}> was stopped after <{}> nanoseconds", name,
                 tags.get(SEGMENT_TAG), durationNano);
-        startedTimer.getOnStopHandlers().forEach(stoppedTimerConsumer -> stoppedTimerConsumer.accept(this));
+        startedTimer.getOnStopHandlers().forEach(stoppedTimerConsumer -> stoppedTimerConsumer.handleStoppedTimer(this));
         getKamonInternalTimer().record(durationNano);
     }
 

internal/utils/metrics/src/test/java/org/eclipse/ditto/internal/utils/metrics/instruments/timer/StartedKamonTimerTest.java

@@ -45,19 +45,19 @@ public void getName() {
 
     @Test
     public void getOnStopHandlers() {
-        final Consumer<StoppedTimer> onStopHandler = mock(Consumer.class);
+        final OnStopHandler onStopHandler = mock(OnStopHandler.class);
         sut.onStop(onStopHandler);
-        final List<Consumer<StoppedTimer>> onStopHandlers = sut.getOnStopHandlers();
+        final List<OnStopHandler> onStopHandlers = sut.getOnStopHandlers();
         Assertions.assertThat(onStopHandlers).hasSize(2);
         Assertions.assertThat(onStopHandlers).contains(onStopHandler);
     }
 
     @Test
     public void onStopIsCalled() {
-        final Consumer<StoppedTimer> onStopHandler = mock(Consumer.class);
+        final OnStopHandler onStopHandler = mock(OnStopHandler.class);
         sut.onStop(onStopHandler);
-        final StoppedTimer stop = sut.stop();
-        verify(onStopHandler).accept(stop);
+        final StoppedTimer stopped = sut.stop();
+        verify(onStopHandler).handleStoppedTimer(stopped);
     }
 
     @Test
@@ -108,14 +108,14 @@ public void segmentsAreGettingStoppedToo() {
 
     @Test
     public void onStopHandlersOfSegmentsAreCalledToo() {
-        final Consumer<StoppedTimer> onStopHandler = mock(Consumer.class);
-        final Consumer<StoppedTimer> segmentOnStopHandler = mock(Consumer.class);
+        final OnStopHandler onStopHandler = mock(OnStopHandler.class);
+        final OnStopHandler segmentOnStopHandler = mock(OnStopHandler.class);
         sut.onStop(onStopHandler);
         final StartedTimer testSegment = sut.startNewSegment("TEST");
         testSegment.onStop(segmentOnStopHandler);
         final StoppedTimer stop = sut.stop();
-        verify(onStopHandler).accept(stop);
-        verify(segmentOnStopHandler).accept(any(StoppedTimer.class));
+        verify(onStopHandler).handleStoppedTimer(stop);
+        verify(segmentOnStopHandler).handleStoppedTimer(any(StoppedTimer.class));
     }
 
     @Test