join and split byte arrays byte[] ?

In this example, we will show you how to join and split byte arrays with ByteBuffer and System.arraycopy.

ByteBuffer

public static byte[] joinByteArray(byte[] byte1, byte[] byte2) {

    return ByteBuffer.allocate(byte1.length + byte2.length)
            .put(byte1)
            .put(byte2)
            .array();

}

public static void splitByteArray(byte[] input) {

    ByteBuffer bb = ByteBuffer.wrap(input);

    byte[] cipher = new byte[8];
    byte[] nonce = new byte[4];
    byte[] extra = new byte[2];
    bb.get(cipher, 0, cipher.length);
    bb.get(nonce, 0, nonce.length);
    bb.get(extra, 0, extra.length);

}

System.arraycopy

public static byte[] joinByteArray(byte[] byte1, byte[] byte2) {

    byte[] result = new byte[byte1.length + byte2.length];

    System.arraycopy(byte1, 0, result, 0, byte1.length);
    System.arraycopy(byte2, 0, result, byte1.length, byte2.length);

    return result;

}

public static void splitByteArray(byte[] input) {

    byte[] cipher = new byte[8];
    byte[] nonce = new byte[4];
    byte[] extra = new byte[2];
    System.arraycopy(input, 0, cipher, 0, cipher.length);
    System.arraycopy(input, cipher.length, nonce, 0, nonce.length);
    System.arraycopy(input, cipher.length + nonce.length, extra, 0, extra.length);

}

1. Join Byte Arrays

This Java example uses ByteBuffer or System.arraycopy to join or concatenate two byte arrays.

JoinByteArrayExample.java

package com.mkyong.nio;

import java.nio.ByteBuffer;

public class JoinByteArrayExample {

    public static void main(String[] args) {

        String str1 = "Hello World ";
        String str2 = "Java";

        byte[] bytes = joinByteArray(str1.getBytes(), str2.getBytes());
        byte[] bytes2 = joinByteArray2(str1.getBytes(), str2.getBytes());

        // byte[] to String
        System.out.println("Result       : " + new String(bytes));
        System.out.println("Result (Hex) : " + convertBytesToHex(bytes));

        System.out.println("Result2      : " + new String(bytes2));
        System.out.println("Result2 (Hex): " + convertBytesToHex(bytes2));

    }

    public static byte[] joinByteArray(byte[] byte1, byte[] byte2) {

        return ByteBuffer.allocate(byte1.length + byte2.length)
                .put(byte1)
                .put(byte2)
                .array();

    }

    public static byte[] joinByteArray2(byte[] byte1, byte[] byte2) {

        byte[] result = new byte[byte1.length + byte2.length];

        System.arraycopy(byte1, 0, result, 0, byte1.length);
        System.arraycopy(byte2, 0, result, byte1.length, byte2.length);

        return result;

    }

    public static String convertBytesToHex(byte[] bytes) {
        StringBuilder result = new StringBuilder();
        for (byte temp : bytes) {
            result.append(String.format("%02x", temp));
        }
        return result.toString();
    }

}

Output Terminal :

Result       : Hello World Java
Result (Hex) : 48656c6c6f20576f726c64204a617661
Result2      : Hello World Java
Result2 (Hex): 48656c6c6f20576f726c64204a617661

2. Split Byte Array

In Java, we can use ByteBuffer or System.arraycopy to split a single byte array into multiple byte arrays.

For example, this 000102030a0b0c0d1a1b1c1d2f2f is a byte array (14 bytes) in hex representation, it is a combined of cipher (8 bytes) + nonce (4 bytes) + extra (2 bytes).

000102030a0b0c0d | 1a1b1c1d | 2f2f
cipher | nonce | extra

SplitByteArrayExample.java

package com.mkyong.nio;

import java.nio.ByteBuffer;

public class SplitByteArrayExample {

    public static void main(String[] args) {

        byte[] input = {0x00, 0x01, 0x02, 0x03, 0x0a, 0x0b, 0x0c, 0x0d, 0x1a, 0x1b, 0x1c, 0x1d, 0x2f, 0x2f};

        if (input.length != 14) {
            throw new IllegalArgumentException("input must be 14 bytes.");
        }

        ByteBuffer bb = ByteBuffer.wrap(input);

        byte[] cipher = new byte[8];
        byte[] nonce = new byte[4];
        byte[] extra = new byte[2];
        bb.get(cipher, 0, cipher.length);
        bb.get(nonce, 0, nonce.length);
        bb.get(extra, 0, extra.length);

        System.out.println("Input (Hex)    : " + convertBytesToHex(input));

        System.out.println("\n--- ByteBuffer ---");
        System.out.println("Cipher(Hex)    : " + convertBytesToHex(cipher));
        System.out.println("Nonce (Hex)    : " + convertBytesToHex(nonce));
        System.out.println("Nonce (Hex)    : " + convertBytesToHex(extra));

        byte[] cipher2 = new byte[8];
        byte[] nonce2 = new byte[4];
        byte[] extra2 = new byte[2];
        System.arraycopy(input, 0, cipher2, 0, cipher2.length);
        System.arraycopy(input, cipher2.length, nonce2, 0, nonce2.length);
        System.arraycopy(input, cipher2.length + nonce2.length, extra2, 0, extra2.length);

        System.out.println("\n--- System.arraycopy ---");
        System.out.println("Cipher2 (Hex)  : " + convertBytesToHex(cipher2));
        System.out.println("Nonce2  (Hex)  : " + convertBytesToHex(nonce2));
        System.out.println("Nonce2  (Hex)  : " + convertBytesToHex(extra2));

    }

    public static String convertBytesToHex(byte[] bytes) {
        StringBuilder result = new StringBuilder();
        for (byte temp : bytes) {
            result.append(String.format("%02x", temp));
        }
        return result.toString();
    }

}

Output Terminal

Input (Hex)    : 000102030a0b0c0d1a1b1c1d2f2f

--- ByteBuffer ---
Cipher(Hex)    : 000102030a0b0c0d
Nonce (Hex)    : 1a1b1c1d
Nonce (Hex)    : 2f2f

--- System.arraycopy ---
Cipher2 (Hex)  : 000102030a0b0c0d
Nonce2  (Hex)  : 1a1b1c1d
Nonce2  (Hex)  : 2f2f

References

Read also : Patterns optionels

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