Question

I have a String that I have to concatenate with an byte array, so I tried this

String msg = "msg to show";

byte[] msgByte = new byte[msg.length()];

try {
msgByte = msg.getBytes("UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}

byte[] command = {2,5,1,5}

byte[] c = new byte[msgByte.length + command.length];
System.arraycopy(command, 0, c, 0, command.length);
System.arraycopy(msjByte, 0, c, command.length, msjByte.length);

for(Byte bt:c)
    System.out.println(bt+"");

This is the output:
2 5 1 5 109 115 103 32 …

but the result that I’m looking for is this
2 5 1 5 m s g …

I need it in one array cause it’s used as a command for a bluetooth printer.

Is there a way, any suggestions?

Thanks in advance! 🙂

Answer 1

You can’t have a byte array containing ‘2 5 1 5 m s g’. From the documentation:

The byte data type is an 8-bit signed two’s complement integer. It has
a minimum value of -128 and a maximum value of 127 (inclusive).

I can’t envisage a scenario where you would actually want to join un-encoded bytes with a string, but here’s a solution that returns a char[].

public static void main(String[] args) {
    final String msg = "msg to show";
    final byte[] command = { 2, 5, 1, 5 };

    // Prints [2, 5, 1, 5, m, s, g,  , t, o,  , s, h, o, w]
    System.out.println(Arrays.toString(concat(msg, command)));
}

private static char[] concat(final byte[] bytes, final String str) {
    final StringBuilder sb = new StringBuilder();
    for (byte b : bytes) {
        sb.append(b);
    }
    sb.append(str);
    return sb.toString().toCharArray();
}