core: Opaque: Cache hashCode value

We may frequently compare Opaques via HashMap.

Cache the #hashCode computation once computed.

Related: #149
Signed-off-by: Christian Kohlschütter <[email protected]>

Author: kohlschuetter

core/src/main/java/org/dcache/nfs/util/Opaque.java

@@ -134,6 +134,7 @@ default void putBytes(ByteBuffer buf) {
     final class OpaqueImpl implements Opaque {
         private final byte[] _opaque;
         private String base64 = null;
+        private int hashCode;
 
         private OpaqueImpl(byte[] opaque) {
             _opaque = opaque;
@@ -159,7 +160,10 @@ public void putBytes(ByteBuffer buf) {
 
         @Override
         public int hashCode() {
-            return Arrays.hashCode(_opaque);
+            if (hashCode == 0) {
+                hashCode = Arrays.hashCode(_opaque);
+            }
+            return hashCode;
         }
 
         @Override