Java9でsun.misc.Cleanerのpackageが移動してしまうことへの対処(Apache Hadoopの場合)

    /**
     * Unmaps the block from memory. See munmap(2).
     *
     * There isn't any portable way to unmap a memory region in Java.
     * So we use the sun.nio method here.
     * Note that unmapping a memory region could cause crashes if code
     * continues to reference the unmapped code.  However, if we don't
     * manually unmap the memory, we are dependent on the finalizer to
     * do it, and we have no idea when the finalizer will run.
     *
     * @param buffer    The buffer to unmap.
     */
    public static void munmap(MappedByteBuffer buffer) {
      if (buffer instanceof sun.nio.ch.DirectBuffer) {
        sun.misc.Cleaner cleaner =
            ((sun.nio.ch.DirectBuffer)buffer).cleaner();
        cleaner.clean();
      }
    }

  private static MethodHandle cleanMethod = null;
  static {
    MethodHandles.Lookup lookup = MethodHandles.lookup();
    try {
      final Class<?> directBufferClass =
          Class.forName("java.nio.DirectByteBuffer");
      final Method m = directBufferClass.getMethod("cleaner");
      // Set permission to the lookup class for making
      // a direct method handle
      m.setAccessible(true);
      // Make a direct method handle
      MethodHandle directbufferCleanerMethod = lookup.unreflect(m);
      // Get the return type of java.nio.DirectByteBuffer
      // JDK8: sun.misc.Cleaner
      // JDK9: jdk.internal.ref.Cleaner
      Class<?> cleanerClass = directbufferCleanerMethod.type().returnType();
      // Get the method (Cleaner#clean)
      cleanMethod = lookup.findVirtual(
          cleanerClass, "clean", methodType(void.class));
    } catch (NoSuchMethodException | IllegalAccessException |
             ClassNotFoundException ignored) {
    }
  }

     public static void munmap(MappedByteBuffer buffer) {
       if (buffer instanceof sun.nio.ch.DirectBuffer) {
         if (cleanMethod != null) {
           try {
             // Execute Cleaner#clean
             cleanMethod.invokeExact(
                 ((sun.nio.ch.DirectBuffer)buffer).cleaner());
           } catch (Throwable ignored) {
           }
         }