How to convert int[] to byte[]

Question

I have an array of integers which represent a RGB image and would like to convert it to a byte array and save it to a file.

What\'s the best way to convert an array

Answer 1

I would use 'DataOutputStream' with 'ByteArrayOutputStream'.

public final class Converter {

    private static final int BYTES_IN_INT = 4;

    private Converter() {}

    public static byte [] convert(int [] array) {
        if (isEmpty(array)) {
            return new byte[0];
        }

        return writeInts(array);
    }

    public static int [] convert(byte [] array) {
        if (isEmpty(array)) {
            return new int[0];
        }

        return readInts(array);
    }

    private static byte [] writeInts(int [] array) {
        try {
            ByteArrayOutputStream bos = new ByteArrayOutputStream(array.length * 4);
            DataOutputStream dos = new DataOutputStream(bos);
            for (int i = 0; i < array.length; i++) {
                dos.writeInt(array[i]);
            }

            return bos.toByteArray();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    private static int [] readInts(byte [] array) {
        try {
            ByteArrayInputStream bis = new ByteArrayInputStream(array);
            DataInputStream dataInputStream = new DataInputStream(bis);
            int size = array.length / BYTES_IN_INT;
            int[] res = new int[size];
            for (int i = 0; i < size; i++) {
                res[i] = dataInputStream.readInt();
            }
            return res;
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

    public class ConverterTest {

    @Test
    public void convert() {
        final int [] array = {-1000000, 24000, -1, 40};
        byte [] bytes = Converter.convert(array);
        int [] array2 = Converter.convert(bytes);

        assertTrue(ArrayUtils.equals(array, array2));

        System.out.println(Arrays.toString(array));
        System.out.println(Arrays.toString(bytes));
        System.out.println(Arrays.toString(array2));
    }
}

Prints:

[-1000000, 24000, -1, 40]
[-1, -16, -67, -64, 0, 0, 93, -64, -1, -1, -1, -1, 0, 0, 0, 40]
[-1000000, 24000, -1, 40]