Best way to encode

Question

I have an array of bytes that contains negative numbers that I need to write to a file and read back into a byte array.

Imagine that I have 10 byte arrays of length 128, including negative numbers.

What would be the best way to write the ten arrays to the same file, such that I could read the file and create the same ten byte arrays again? I know that there will always be of length 128, so that is not an issue.

I currently tried putting them all into one string, encoding it with base 64, and writing that to file. However, when I read the file and decoded it, it didn't seem to interpret it properly (the first array was in order, the other was not).

Any ideas?

Answer 1

Just write them out directly to an OutputStream - there's no need to encode them:

// Or wherever you get them from
byte[][] arrays = new byte[10][128];
...

for (byte[] array : arrays) {
    outputStream.write(array);
}

Then when reading (with an InputStream ):

byte[][] arrays = new byte[10][];
for (int i = 0; i < arrays.length; i++) {
    arrays[i] = readExactly(inputStream, 128);
}

...

private static byte[] readExactly(InputStream input, int size) throws IOException {
    byte[] ret = new byte[size];
    int bytesRemaining = size;
    while (bytesRemaining > 0) {
        int bytesRead = input.read(ret, size - bytesRemaining, bytesRemaining);
        if (bytesRead == -1) {
            throw new IOException("Ran out of data");
        }
    }
    return ret;
}

Note that you can't just issue 10 calls to InputStream.read and assume it will read 128 bytes each time.