Question

I do not have experience using Java channels. I would like to write a byte array to a file. Currently, I have the following code:

String outFileString = DEFAULT_DECODED_FILE; // Valid file pathname
FileSystem fs = FileSystems.getDefault();
Path fp = fs.getPath(outFileString);

FileChannel outChannel = FileChannel.open(fp, EnumSet.of(StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.WRITE));

// Please note: result.getRawBytes() returns a byte[]
ByteBuffer buffer = ByteBuffer.allocate(result.getRawBytes().length);
buffer.put(result.getRawBytes());

outChannel.write(buffer); // File successfully created/truncated, but no data

With this code, the output file is created, and truncated if it exists. Also, in the IntelliJ debugger, I can see that buffer contains data. Also, the line outChannel.write() is successfully called without throwing an exception. However, after the program exits, the data does not appear in the output file.

Can somebody (a) tell me if the FileChannel API is an acceptable choice for writing a byte array to a file, and (b) if so, how should the above code be modified to get it to work?

Answer 1

As gulyan points out, you need to flip() your byte buffer before writing it. Alternately, you could wrap your original byte array:

ByteBuffer buffer = ByteBuffer.wrap(result.getRawBytes());

To guarantee the write is on disk, you need to use force():

outChannel.force(false);

Or you could close the channel:

outChannel.close();