Utils.java

import java.io.*;
import java.util.Arrays;

/**
 * Created by yasin_000 on 1.5.2019.
 */
public class Utils {

    public static byte[] fileToBytes(File f) throws IOException{
        InputStream fis = new FileInputStream(f);
        if (f.length() > Integer.MAX_VALUE)
            throw new IOException("File size is too big.");
        ByteArrayOutputStream baos = new ByteArrayOutputStream((int) f.length());
        byte[] buffer = new byte[8 * 1024];

        int bytesRead;
        while ((bytesRead = fis.read(buffer)) != -1) {
            baos.write(buffer, 0, bytesRead);
        }
        fis.close();

        return baos.toByteArray();
    }

    public static void bytesToFile(byte[] bytes, File file) {
        BufferedOutputStream bos = null;
        try {
            bos = new BufferedOutputStream(new FileOutputStream(file));
            bos.write(bytes);
            bos.flush();
            System.out.println(bos.toString());
            System.out.println(Arrays.toString(bytes));
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (bos != null)
                    bos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static byte[] intToBytes(int number) {
        return new byte[]{
                (byte) ((number >>> 24) & 0xff),
                (byte) ((number >>> 16) & 0xff),
                (byte) ((number >>> 8) & 0xff),
                (byte) (number & 0xff)
        };
    }

    public static int bytesToInt(byte[] bytes) {
        return ((bytes[0] & 0xff) << 24) |
                ((bytes[1] & 0xff) << 16) |
                ((bytes[2] & 0xff) << 8) |
                (bytes[3] & 0xff);
    }

    /*
     * Combines given byte arrays into one byte array
     */
    public static byte[] createPacket(byte[]... bytes) {
        int offset = 0;
        int totalLength = 0;
        for (int i = 0; i < bytes.length; i++) {
            totalLength += bytes[i].length;
        }

        byte[] packet = new byte[totalLength];
        for (int i = 0; i < bytes.length; i++) {
            if (bytes[i].length <= 0)
                continue;
            System.arraycopy(bytes[i], 0, packet, offset, bytes[i].length);
            offset += bytes[i].length;
        }

        return packet;
    }


}