FEAT StopWatch procedural/functional time measurement

src/main/java/de/nclazz/commons/StopWatch.java

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+package de.nclazz.commons;
+
+import lombok.NonNull;
+
+import java.time.Clock;
+import java.util.function.LongConsumer;
+import java.util.function.Supplier;
+
+public class StopWatch {
+
+    private final Clock clock;
+    private long tStart;
+    private long tEnd;
+    private long finalTime = -1;
+
+    private LongConsumer elapsedTimeConsumer;
+
+
+    private StopWatch(Clock clock) {
+        this.clock = clock;
+    }
+
+    public StopWatch onCompleted(LongConsumer consumer) {
+        this.elapsedTimeConsumer = consumer;
+        return this;
+    }
+
+    public long getTimeStart() {
+        return this.tStart;
+    }
+
+    public long getTimeEnd() {
+        return this.tEnd;
+    }
+
+    public long getElapsedTime() {
+        return this.finalTime;
+    }
+
+    public <T> T measure(Supplier<T> supplier) {
+        this.tStart = this.clock.millis();
+
+        T result = supplier.get();
+
+        this.tEnd = this.clock.millis();
+        this.finalTime = this.tEnd - this.tStart;
+
+        return result;
+    }
+
+    public void measure(Runnable runnable) {
+        measure(emptySupplier(runnable));
+    }
+
+    private Supplier<Void> emptySupplier(Runnable runnable) {
+        return () -> {
+            runnable.run();
+            return null;
+        };
+    }
+
+    public static StopWatch defaultTimer() {
+        return new StopWatch(Clock.systemDefaultZone());
+    }
+
+    public static StopWatch forClock(@NonNull Clock clock) {
+        return new StopWatch(clock);
+    }
+
+
+}

src/test/java/de/nclazz/commons/MockupClock.java

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+package de.nclazz.commons;
+
+import java.time.Clock;
+import java.time.Instant;
+import java.time.ZoneId;
+
+/**
+ * Mockup Clock that increments millis about 10 units,
+ * whenever the {@link #millis()} method is called;
+ */
+public class MockupClock extends Clock {
+
+    private long t = -10;
+
+    @Override
+    public long millis() {
+        t += 10;
+        return t;
+    }
+
+    @Override
+    public ZoneId getZone() {
+        return null;
+    }
+
+    @Override
+    public Clock withZone(ZoneId zone) {
+        return null;
+    }
+
+    @Override
+    public Instant instant() {
+        return null;
+    }
+}

src/test/java/de/nclazz/commons/StopWatchTests.java

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+package de.nclazz.commons;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class StopWatchTests {
+
+    @Test
+    void testProceduralUsage() {
+        StopWatch watch = StopWatch.forClock(new MockupClock());
+
+        String value = watch.measure(() -> "Hello World");
+
+        assertEquals("Hello World", value);
+        assertEquals(10, watch.getElapsedTime());
+    }
+
+    @Test
+    void testFunctionalUsage() {
+
+        String value = StopWatch.forClock(new MockupClock())
+                            .onCompleted(elapsed -> assertEquals(10, elapsed))
+                            .measure(() -> "Hello World");
+        
+        assertEquals("Hello World", value);
+    }
+
+}