Merge pull request #15106 from hangga/generate-unique-long

BAEL-6430 : Generate unique long using UUID | Hangga Aji Sayekti

core-java-modules/core-java-uuid/src/main/java/com/baeldung/uuid/UUIDPositiveLongGenerator.java

@@ -0,0 +1,83 @@
+package com.baeldung.uuid;
+
+import java.nio.ByteBuffer;
+import java.security.SecureRandom;
+import java.util.UUID;
+
+/**
+ * Methods are called by reflection in the unit test
+ */
+@SuppressWarnings("unused")
+public class UUIDPositiveLongGenerator {
+    public long getLeastSignificantBits() {
+        return Math.abs(UUID.randomUUID().getLeastSignificantBits());
+    }
+
+    public long getMostSignificantBits() {
+        return Math.abs(UUID.randomUUID().getMostSignificantBits());
+    }
+
+    public long combineByteBuffer() {
+        UUID uuid = UUID.randomUUID();
+        ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
+        bb.putLong(uuid.getMostSignificantBits());
+        bb.putLong(uuid.getLeastSignificantBits());
+        bb.rewind();
+        return Math.abs(bb.getLong());
+    }
+
+    public long combineBitwise() {
+        UUID uniqueUUID = UUID.randomUUID();
+        long mostSignificantBits = uniqueUUID.getMostSignificantBits();
+        long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
+        return Math.abs((mostSignificantBits << 32) | (leastSignificantBits & 0xFFFFFFFFL));
+    }
+
+    public long combineDirect() {
+        UUID uniqueUUID = UUID.randomUUID();
+        long mostSignificantBits = uniqueUUID.getMostSignificantBits();
+        long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
+        return Math.abs(mostSignificantBits ^ (leastSignificantBits >> 1));
+    }
+
+    public long combinePermutation() {
+        UUID uuid = UUID.randomUUID();
+        long mostSigBits = uuid.getMostSignificantBits();
+        long leastSigBits = uuid.getLeastSignificantBits();
+        byte[] uuidBytes = new byte[16];
+
+        for (int i = 0; i < 8; i++) {
+            uuidBytes[i] = (byte) (mostSigBits >>> (8 * (7 - i)));
+            uuidBytes[i + 8] = (byte) (leastSigBits >>> (8 * (7 - i)));
+        }
+
+        long result = 0;
+        for (byte b : uuidBytes) {
+            result = (result << 8) | (b & 0xFF);
+        }
+        return Math.abs(result);
+    }
+
+    public long combineWithSecureRandom() {
+        UUID uniqueUUID = UUID.randomUUID();
+        SecureRandom secureRandom = new SecureRandom();
+        long randomBits = secureRandom.nextLong();
+
+        long mostSignificantBits = uniqueUUID.getMostSignificantBits() ^ randomBits;
+        long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
+
+        return Math.abs((mostSignificantBits << 32) | (leastSignificantBits & 0xFFFFFFFFL));
+    }
+
+    public long combineWithNanoTime() {
+        UUID uniqueUUID = UUID.randomUUID();
+        long nanoTime = System.nanoTime();
+
+        long mostSignificantBits = uniqueUUID.getMostSignificantBits() ^ nanoTime;
+        long leastSignificantBits = uniqueUUID.getLeastSignificantBits();
+
+        return Math.abs((mostSignificantBits << 32) | (leastSignificantBits & 0xFFFFFFFFL));
+    }
+
+
+}

core-java-modules/core-java-uuid/src/test/java/com/baeldung/uuid/UUIDPositiveLongGeneratorUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.uuid;
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Method;
+import java.util.HashSet;
+import java.util.Set;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class UUIDPositiveLongGeneratorUnitTest {
+
+    private final UUIDPositiveLongGenerator uuidLongGenerator = new UUIDPositiveLongGenerator();
+
+    private final Set<Long> uniqueValues = new HashSet<>();
+
+    @Test
+    void whenForeachMethods_thenRetryWhileNotUnique() throws Exception {
+        for (Method method : uuidLongGenerator.getClass().getDeclaredMethods()) {
+            long uniqueValue;
+            do uniqueValue = (long) method.invoke(uuidLongGenerator); while (!isUnique(uniqueValue));
+            assertThat(uniqueValue).isPositive();
+        }
+    }
+
+    @Test
+    void whenGivenLongValue_thenCheckUniqueness() {
+        long uniqueValue = generateUniqueLong();
+        assertThat(uniqueValue).isPositive();
+    }
+
+    private long generateUniqueLong() {
+        long uniqueValue;
+        do uniqueValue = uuidLongGenerator.combineBitwise(); while (!isUnique(uniqueValue));
+        return uniqueValue;
+    }
+
+    private boolean isUnique(long value) {
+        // Implement uniqueness checking logic, for example, by checking in the database
+        return uniqueValues.add(value);
+    }
+
+}

core-java-modules/core-java-uuid/src/test/resources/logback.xml

@@ -2,8 +2,7 @@
 <configuration>
     <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
         <encoder>
-            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
-            </pattern>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
         </encoder>
     </appender>