How to save a Java FloatBuffer (or any Buffer) to a file

Question

I have a FloatBuffer of known size and just want to dump the data to a file (in binary) for inspection outside my app. What's the easiest way to do this?

Answer 1

UPDATE FOR BINARY OUTPUT:

// There are dependencies on how you create your floatbuffer for this to work
// I suggest starting with a byte buffer and using asFloatBuffer() when
// you need it as floats.
// ByteBuffer b = ByteBuffer.allocate(somesize);
// FloatBuffer fb = b.asFloatBuffer();
// There will also be endiance issues when you write binary since
// java is big-endian. You can adjust this with Buffer.order(...)
// b.order(ByteOrder.LITTLE_ENDIAN)
// If you're using a hex-editor you'll probably want little endian output
// since most consumer machines (unless you've got a sparc / old mac) are little


FileOutputStream fos = new FileOutputStream("some_binary_output_file_name");
FileChannel channel = fos.getChannel();

channel.write(byteBufferBackingYourFloatBuffer);

fos.close();

TEXT OUTPUT: Since you want this to be viewable I assume you want a text file. You'll want to use a PrintStream.

// Try-catch omitted for simplicity

PrintStream ps = new PrintStream("some_output_file.txt");
for(int i = 0; i < yourFloatBuffer.capacity(); i++)
{
   // put each float on one line
   // use printf to get fancy (decimal places, etc)
   ps.println(yourFloagBuffer.get(i));
}

ps.close();

Didn't have time to post a full raw/binary (non-text) version of this. If you want to do that use a FileOutputStream, get the FileChannel, and directly write the FloatBuffer (since it's a ByteBuffer)

Answer 2

This iterates through the array backed by your buffer and outputs each float. Just replace the text file and floatBuffer with your own parameters.

PrintStream out = new PrintStream("target.txt");
for(float f : floatBuffer.array()){
  out.println(f);
}
out.close();

Answer 3

Asusming you want the data as binary:

Start with a ByteBuffer. Call asFloatBuffer to get your FloatBuffer. When you've finished doing your stuff, save the ByteBuffer out to a WritableByteChannel.

If you already have FloatBuffer it can be copied into the buffer from step 2 with a put.

A low performance but easier way would be to use Float.floatToIntBit.

(Watch for endianess, obviously.)