From f66bfa5088c996465d5e6729f61b0185badbcd8e Mon Sep 17 00:00:00 2001
From: Diego Torres <dtorres.py@gmail.com>
Date: Thu, 24 Jun 2021 16:10:31 -0400
Subject: [PATCH] [uuid] Added method to generate UUID identifiers for version
 5 (#10948)

Signed-off-by: Diego Torres <dtorres.py@gmail.com>
---
 .../java/com/baeldung/uuid/UUIDGenerator.java | 56 ++++++++++++++++---
 .../baeldung/uuid/UUIDGeneratorUnitTest.java  | 10 ++++
 2 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/core-java-modules/core-java/src/main/java/com/baeldung/uuid/UUIDGenerator.java b/core-java-modules/core-java/src/main/java/com/baeldung/uuid/UUIDGenerator.java
index cb43a26929..49d43c38a2 100644
--- a/core-java-modules/core-java/src/main/java/com/baeldung/uuid/UUIDGenerator.java
+++ b/core-java-modules/core-java/src/main/java/com/baeldung/uuid/UUIDGenerator.java
@@ -1,6 +1,8 @@
 package com.baeldung.uuid;
 
 import java.io.UnsupportedEncodingException;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.time.Duration;
@@ -132,21 +134,21 @@ public class UUIDGenerator {
     }
 
     private static byte[] bytesFromUUID(String uuidHexString) {
-        String normalizedUUIDHexString = uuidHexString.replace("-","");
+        String normalizedUUIDHexString = uuidHexString.replace("-", "");
 
         assert normalizedUUIDHexString.length() == 32;
 
         byte[] bytes = new byte[16];
         for (int i = 0; i < 16; i++) {
-            byte b = hexToByte(normalizedUUIDHexString.substring(i*2, i*2+2));
+            byte b = hexToByte(normalizedUUIDHexString.substring(i * 2, i * 2 + 2));
             bytes[i] = b;
         }
         return bytes;
     }
 
     public static byte hexToByte(String hexString) {
-        int firstDigit = Character.digit(hexString.charAt(0),16);
-        int secondDigit = Character.digit(hexString.charAt(1),16);
+        int firstDigit = Character.digit(hexString.charAt(0), 16);
+        int secondDigit = Character.digit(hexString.charAt(1), 16);
         return (byte) ((firstDigit << 4) + secondDigit);
     }
 
@@ -154,14 +156,54 @@ public class UUIDGenerator {
         int finalLength = byteArray1.length + byteArray2.length;
         byte[] result = new byte[finalLength];
 
-        for(int i = 0; i < byteArray1.length; i++) {
+        for (int i = 0; i < byteArray1.length; i++) {
             result[i] = byteArray1[i];
         }
 
-        for(int i = 0; i < byteArray2.length; i++) {
-            result[byteArray1.length+i] = byteArray2[i];
+        for (int i = 0; i < byteArray2.length; i++) {
+            result[byteArray1.length + i] = byteArray2[i];
         }
 
         return result;
     }
+
+    public static UUID generateType5UUID(String name) {
+
+        try {
+
+            byte[] bytes = name.getBytes(StandardCharsets.UTF_8);
+            MessageDigest md = MessageDigest.getInstance("SHA-1");
+
+            byte[] hash = md.digest(bytes);
+
+            long msb = peekLong(hash, 0, ByteOrder.BIG_ENDIAN);
+            long lsb = peekLong(hash, 8, ByteOrder.BIG_ENDIAN);
+            // Set the version field
+            msb &= ~(0xfL << 12);
+            msb |= ((long) 5) << 12;
+            // Set the variant field to 2
+            lsb &= ~(0x3L << 62);
+            lsb |= 2L << 62;
+            return new UUID(msb, lsb);
+
+        } catch (NoSuchAlgorithmException e) {
+            throw new AssertionError(e);
+        }
+    }
+
+    private static long peekLong(final byte[] src, final int offset, final ByteOrder order) {
+        long ans = 0;
+        if (order == ByteOrder.BIG_ENDIAN) {
+            for (int i = offset; i < offset + 8; i += 1) {
+                ans <<= 8;
+                ans |= src[i] & 0xffL;
+            }
+        } else {
+            for (int i = offset + 7; i >= offset; i -= 1) {
+                ans <<= 8;
+                ans |= src[i] & 0xffL;
+            }
+        }
+        return ans;
+    }
 }
\ No newline at end of file
diff --git a/core-java-modules/core-java/src/test/java/com/baeldung/uuid/UUIDGeneratorUnitTest.java b/core-java-modules/core-java/src/test/java/com/baeldung/uuid/UUIDGeneratorUnitTest.java
index 9e08363a63..b2ca979c83 100644
--- a/core-java-modules/core-java/src/test/java/com/baeldung/uuid/UUIDGeneratorUnitTest.java
+++ b/core-java-modules/core-java/src/test/java/com/baeldung/uuid/UUIDGeneratorUnitTest.java
@@ -61,4 +61,14 @@ class UUIDGeneratorUnitTest {
         assertEquals(5, uuid.version());
         assertEquals(2, uuid.variant());
     }
+
+    @Test
+    public void version_5_UUID_is_correctly_generated_for_domain_baeldung_com_without_namespace() throws UnsupportedEncodingException {
+
+        UUID uuid = UUIDGenerator.generateType5UUID("baeldung.com");
+
+        assertEquals("a3c27ab0-2b46-55ef-b50e-0e5c57bfea94", uuid.toString());
+        assertEquals(5, uuid.version());
+        assertEquals(2, uuid.variant());
+    }
 }
\ No newline at end of file