Deterministic UUID option for PatternLayout

log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/UuidTest.java

@@ -20,6 +20,8 @@
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.UUID;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.test.layout.LogEventFixtures;
 import org.junit.jupiter.api.Test;
 
 public class UuidTest {
@@ -107,6 +109,20 @@ public void testThreads() throws Exception {
         assertEquals(0, errors, errors + " duplicate UUIDS");
     }
 
+    @Test
+    public void testHashBasedUuid() {
+        LogEvent event1 = LogEventFixtures.createLogEvent();
+        LogEvent event2 = LogEventFixtures.createLogEvent()
+                .asBuilder()
+                .setThrown(event1.getThrown())
+                .build();
+        UUID uuid1 = UuidUtil.getHashBasedUuid(event1);
+        UUID uuid2 = UuidUtil.getHashBasedUuid(event2);
+        assertEquals(uuid1, uuid2, "UUIDs don't match");
+        assertEquals(8, uuid1.version(), "Wrong version");
+        assertEquals(2, uuid1.variant(), "Wrong variant");
+    }
+
     private static class Worker extends Thread {
 
         private final UUID[] uuids;

log4j-core/src/main/java/org/apache/logging/log4j/core/pattern/UuidPatternConverter.java

@@ -29,40 +29,60 @@
 @Plugin("UuidPatternConverter")
 @ConverterKeys({"u", "uuid"})
 public final class UuidPatternConverter extends LogEventPatternConverter {
+    private enum UuidType {
+        TIME,
+        RANDOM,
+        HASH
+    }
 
-    private final boolean isRandom;
+    private final UuidType uuidType;
 
     /**
      * Private constructor.
      */
-    private UuidPatternConverter(final boolean isRandom) {
+    private UuidPatternConverter(final UuidType uuidType) {
         super("u", "uuid");
-        this.isRandom = isRandom;
+        this.uuidType = uuidType;
     }
 
     /**
-     * Obtains an instance of SequencePatternConverter.
+     * Obtains an instance of UuidPatternConverter.
      *
-     * @param options options, currently ignored, may be null.
-     * @return instance of SequencePatternConverter.
+     * @param options options
+     * @return instance of UuidPatternConverter.
      */
     public static UuidPatternConverter newInstance(final String[] options) {
         if (options.length == 0) {
-            return new UuidPatternConverter(false);
+            return new UuidPatternConverter(UuidType.TIME);
         }
 
-        if (options.length > 1 || (!options[0].equalsIgnoreCase("RANDOM") && !options[0].equalsIgnoreCase("Time"))) {
-            LOGGER.error("UUID Pattern Converter only accepts a single option with the value \"RANDOM\" or \"TIME\"");
+        if (options.length == 1) {
+            switch (options[0].toUpperCase()) {
+                case "TIME":
+                    return new UuidPatternConverter(UuidType.TIME);
+                case "RANDOM":
+                    return new UuidPatternConverter(UuidType.RANDOM);
+                case "HASH":
+                    return new UuidPatternConverter(UuidType.HASH);
+            }
         }
-        return new UuidPatternConverter(options[0].equalsIgnoreCase("RANDOM"));
+
+        LOGGER.error(
+                "UUID Pattern Converter only accepts a single option with the value \"TIME\" or \"RANDOM\" or \"HASH\"");
+        return new UuidPatternConverter(UuidType.TIME);
     }
 
     /**
      * {@inheritDoc}
      */
     @Override
     public void format(final LogEvent event, final StringBuilder toAppendTo) {
-        final UUID uuid = isRandom ? UUID.randomUUID() : UuidUtil.getTimeBasedUuid();
+        final UUID uuid =
+                switch (uuidType) {
+                    case TIME -> UuidUtil.getTimeBasedUuid();
+                    case RANDOM -> UUID.randomUUID();
+                    case HASH -> UuidUtil.getHashBasedUuid(event);
+                };
         toAppendTo.append(uuid.toString());
     }
 }