String and byte array concatenation

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! :)

You have the right result. ascii(109) = m. Is this a fairly low level interface, mixing command codes with strings? — Jochen Bedersdorfer
– Jochen Bedersdorfer, Commented Aug 6, 2011 at 2:30
My mistake, I thought that I was missing something with the ASCII codes in the array because the example command for the printer come something like this: byte[] ESC_Z2 = {0x1b, 0x5a, 0x00 , 0x51, 0x05, 0x14 , 0x00 ,'m', 'e', 's', 's','a','g','e' }; So I tried sending the pure ASCII code and it didn't work, but it was due a parameter on the command — dev mz
– dev mz, Commented Aug 6, 2011 at 3:13

hoipolloi · Accepted Answer · 2011-08-06 00:05:30Z

4

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();
}

edited Aug 6, 2011 at 0:05

answered Aug 6, 2011 at 0:00

hoipolloi

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Comments

fireshadow52 · Accepted Answer · 2011-08-06 00:32:36Z

1

An alternative would be to do this...

String msg = "msg to show";
char[] letters = msg.toCharArray();
byte[] command = {2,5,1,5};
String result;
for (String str: command) {
    result += str + " ";
}
for (String str: letters) {
    result += str + " ";
}
System.out.println(result);

edited Aug 6, 2011 at 0:32

answered Aug 6, 2011 at 0:08

fireshadow52

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4 Comments

Jochen Bedersdorfer Over a year ago

you can have characters in bytes, you just need to know what you are doing. There is nothing wrong in presenting chars < 127 as bytes as long as you are clear on the encoding.

fireshadow52 Over a year ago

Thank you for catching that! I'll change my answer.

hoipolloi Over a year ago

@Jochen: I disagree. The OP clearly states that the result he's looking for is '2 5 1 5 m s g'. A byte array can only contain integers. I know what you mean but the OP was not satisfied with 'encoding' the characters as he already tried that (2 5 1 5 109 115 103 32).

Jochen Bedersdorfer Over a year ago

which, if 2 is the value of command byte he wants to send, is just a matter of interpretation.

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