Preserve Java 8 buffer descriptors in persisted Map I/O

src/main/java/net/openhft/chronicle/hash/impl/VanillaChronicleHash.java

@@ -37,6 +37,7 @@
 import java.io.RandomAccessFile;
 import java.lang.ref.WeakReference;
 import java.lang.reflect.Type;
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
@@ -425,7 +426,8 @@ public final void initBeforeMapping(@NotNull final File file,
                     throw throwRecoveryOrReturnIOException(file, "truncated", recover);
                 }
             }
-            globalMutableStateBuffer.flip();
+            //! Keep the Java 8 Buffer descriptor when this reopening path is compiled on newer JDKs.
+            ((Buffer) globalMutableStateBuffer).flip();
             //noinspection unchecked
             globalMutableState.bytesStore(BytesStore.wrap(globalMutableStateBuffer), 0, globalMutableState.maxSize());
         }

src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java

@@ -41,6 +41,7 @@
 import java.io.*;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Modifier;
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.util.HashMap;
@@ -356,7 +357,8 @@ private static void writeNotComplete(@NotNull final FileChannel fileChannel,
                                          final int headerSize) throws IOException {
         //noinspection PointlessBitwiseExpression
         headerBuffer.putInt(SIZE_WORD_OFFSET, NOT_COMPLETE | DATA | headerSize);
-        headerBuffer.clear().position(SIZE_WORD_OFFSET).limit(SIZE_WORD_OFFSET + 4);
+        //! Buffer views preserve Java 8 call descriptors when compiling on newer JDKs.
+        ((Buffer) headerBuffer).clear().position(SIZE_WORD_OFFSET).limit(SIZE_WORD_OFFSET + 4);
         writeFully(fileChannel, SIZE_WORD_OFFSET, headerBuffer);
     }
 
@@ -388,11 +390,12 @@ private static <K, V> ByteBuffer writeHeader(@NotNull final FileChannel fileChan
         headerBuffer.putInt(SIZE_WORD_OFFSET, NOT_COMPLETE | DATA | headerSize);
 
         // Write the size-prefixed blob to the file
-        headerBuffer.position(0);
-        headerBuffer.limit(headerLimit);
+        final Buffer headerView = headerBuffer;
+        headerView.position(0);
+        headerView.limit(headerLimit);
         writeFully(fileChannel, 0, headerBuffer);
 
-        headerBuffer.position(SELF_BOOTSTRAPPING_HEADER_OFFSET);
+        headerView.position(SELF_BOOTSTRAPPING_HEADER_OFFSET);
         return headerBuffer;
     }
 
@@ -406,7 +409,7 @@ private static void commitChronicleMapReady(@NotNull final VanillaChronicleHash
 
         //noinspection PointlessBitwiseExpression
         headerBuffer.putInt(SIZE_WORD_OFFSET, READY | DATA | headerSize);
-        headerBuffer.clear().position(SIZE_WORD_OFFSET).limit(SIZE_WORD_OFFSET + 4);
+        ((Buffer) headerBuffer).clear().position(SIZE_WORD_OFFSET).limit(SIZE_WORD_OFFSET + 4);
         writeFully(fileChannel, SIZE_WORD_OFFSET, headerBuffer);
     }
 
@@ -446,7 +449,7 @@ private static ByteBuffer readSelfBootstrappingHeader(@NotNull final File file,
                 throw new IOException("file=" + file + ": sizeWord is not ready: " + sizeWord);
             }
         }
-        headerBuffer.position(SELF_BOOTSTRAPPING_HEADER_OFFSET);
+        ((Buffer) headerBuffer).position(SELF_BOOTSTRAPPING_HEADER_OFFSET);
         return headerBuffer;
     }
 
@@ -1789,7 +1792,7 @@ private int waitUntilReady(@NotNull final RandomAccessFile raf,
         for (int attempt = 0; attempt < attempts; attempt++) {
             if (raf.length() >= SELF_BOOTSTRAPPING_HEADER_OFFSET) {
 
-                sizeWordBuffer.clear();
+                ((Buffer) sizeWordBuffer).clear();
                 readFully(fileChannel, SIZE_WORD_OFFSET, sizeWordBuffer);
                 if (sizeWordBuffer.remaining() == 0) {
                     int sizeWord = sizeWordBuffer.getInt(0);

src/test/java/net/openhft/chronicle/map/PersistedMapHeaderTest.java

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2013-2025 chronicle.software; SPDX-License-Identifier: Apache-2.0
+ */
+package net.openhft.chronicle.map;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.io.IOException;
+
+import static org.junit.Assert.assertEquals;
+
+public class PersistedMapHeaderTest {
+    @Rule
+    public final TemporaryFolder temporaryFolder = TemporaryFolder.builder().assureDeletion().build();
+
+    @Test
+    public void createReopenAndRecoverPreserveEntries() throws IOException {
+        File file = temporaryFolder.newFile("header.map");
+        ChronicleMapBuilder<Long, Long> builder = ChronicleMap.of(Long.class, Long.class).entries(10);
+
+        try (ChronicleMap<Long, Long> created = builder.createPersistedTo(file)) {
+            created.put(1L, 42L);
+            assertEquals(Long.valueOf(42L), created.get(1L));
+        }
+        try (ChronicleMap<Long, Long> reopened = builder.createPersistedTo(file)) {
+            assertEquals(Long.valueOf(42L), reopened.get(1L));
+            reopened.put(2L, 43L);
+        }
+        try (ChronicleMap<Long, Long> recovered = builder.recoverPersistedTo(file, true)) {
+            assertEquals(2, recovered.size());
+            assertEquals(Long.valueOf(42L), recovered.get(1L));
+            assertEquals(Long.valueOf(43L), recovered.get(2L));
+        }
+        try (ChronicleMap<Long, Long> reopened = builder.createPersistedTo(file)) {
+            assertEquals(2, reopened.size());
+            assertEquals(Long.valueOf(42L), reopened.get(1L));
+            assertEquals(Long.valueOf(43L), reopened.get(2L));
+        }
+    }
+}