Using Java AES CBC mode to encrypt or decrypt data

Put two byte[] into one using this method:

public static byte[] add(byte[] a, byte[] b){
	byte[] data = new byte[a.length + b.length];
	System.arraycopy(a, 0, data, 0, a.length); 
	System.arraycopy(b, 0, data, a.length, b.length); 
	return data;
}

Change HexString to byte[] :

public static byte[] hex_to_bytes(String hexString){
	char[] hex = hexString.toCharArray();
	int length = hex.length / 2;
	byte[] rawData = new byte[length];
	for (int i = 0; i < length; i++){
		int high = Character.digit(hex[i * 2], 16);
		int low = Character.digit(hex[i * 2 + 1], 16);
		int value = (high << 4) | low;
		if (value > 127){
			value -= 256;
		}			
		rawData [i] = (byte) value;
	}
	 return rawData ;
}

Change byte[] to HexString :

public static String byte_to_Hex(byte[] data){
	hexString = "";
	for(int i=0; i<b.length ; i++){
		hexString += Integer.toString((b[i] & 0xff) + 0x100,16).substring(1);
	}
	return hexString;
}