time-based UUIDs

core-java-modules/core-java-uuid/src/main/java/com/baeldung/timebaseduuid/JavaUUIDCreator.java

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+package com.baeldung.timebaseduuid;
+
+import com.fasterxml.uuid.Generators;
+import com.github.f4b6a3.uuid.UuidCreator;
+
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class JavaUUIDCreator {
+
+    public static void main(String[] args) throws InterruptedException {
+
+        int threadCount = 128;
+        int iterationCount = 100_000;
+        ConcurrentMap<UUID, Long> uuidMap = new ConcurrentHashMap<>();
+        AtomicLong collisionCount = new AtomicLong();
+        long startNanos = System.nanoTime();
+        CountDownLatch endLatch = new CountDownLatch(threadCount);
+
+        for (long i = 0; i < threadCount; i++) {
+            final long threadId = i;
+            new Thread(() -> {
+                for (long j = 0; j < iterationCount; j++) {
+                    UUID uuid = Generators.timeBasedGenerator().generate();
+                    Long existingUUID = uuidMap.put(uuid, (threadId * iterationCount) + j);
+                    if(existingUUID != null) {
+                        collisionCount.incrementAndGet();
+                    }
+                }
+                endLatch.countDown();
+            }).start();
+        }
+
+        endLatch.await();
+        System.out.println(threadCount * iterationCount + " UUIDs generated, " + collisionCount + " collisions in "
+                + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNanos) + "ms");
+    }
+}

core-java-modules/core-java-uuid/src/main/java/com/baeldung/timebaseduuid/UUIDCreator.java

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+package com.baeldung.timebaseduuid;
+
+import com.github.f4b6a3.uuid.UuidCreator;
+
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
+
+public class UUIDCreator {
+
+    public static void main(String[] args) throws InterruptedException {
+
+        int threadCount = 128;
+        int iterationCount = 100_000;
+        ConcurrentMap<UUID, Long> uuidMap = new ConcurrentHashMap<>();
+        AtomicLong collisionCount = new AtomicLong();
+        long startNanos = System.nanoTime();
+        CountDownLatch endLatch = new CountDownLatch(threadCount);
+
+        for (long i = 0; i < threadCount; i++) {
+            final long threadId = i;
+            new Thread(() -> {
+                for (long j = 0; j < iterationCount; j++) {
+                    UUID uuid = UuidCreator.getTimeBased();
+                    Long existingUUID = uuidMap.put(uuid, (threadId * iterationCount) + j);
+                    if(existingUUID != null) {
+                        collisionCount.incrementAndGet();
+                    }
+                }
+                endLatch.countDown();
+            }).start();
+        }
+
+        endLatch.await();
+        System.out.println(threadCount * iterationCount + " UUIDs generated, " + collisionCount + " collisions in "
+                + TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startNanos) + "ms");
+    }
+}