Question

Is there a programmatical way to implement the method “isFileMapped” which satisfy the following:

 ByteBuffer aa = ByteBuffer.allocateDirect(12);
 assertFalse(isFileMapped(aa));
 FileChannel fc = new RandomAccessFile(File.createTempFile("mmap", "test"), "rw").getChannel();
 ByteBuffer bb = fc.map(FileChannel.MapMode.READ_WRITE, 0, 10);
 assertTrue(isFileMapped(bb));
 fc.close();
 // and of course:
 assertFalse(isFileMapped(ByteBuffer.allocate(12)));

Both instances are of type MappedByteBuffer and are direct.

Answer 1

Use MappedByteBuffer.isLoaded(). For really mapped buffers it returns true or false, for those returned by ByteBuffer.allocateDirect(), it throws UnsupportedOperationException.

But I am not sure if it would still throw UnsupportedOperationException after participating in an I/O operation.