Sending a sysex message in Java

Question

I'm trying to make an application that will send a sysex message to a Roland device. I found an example and tried to modify it a bit for my own needs:

protected void transmitSYSEX(String byteString)
{
    SysexMessage sysx = new SysexMessage();
    int lengthInBytes = byteString.length() / 2;
    byte sysxMsg[] = new byte[lengthInBytes];

    String message = "";

    for (int i = 0; i < lengthInBytes; i++) 
    {
        sysxMsg[i] = (byte) Integer.parseInt(
        byteString.substring(i * 2, i * 2 + 1), 16);
    }

    for (int i = 0 ; i < sysxMsg.length ; i++)
        message += sysxMsg[i];

    textView.setText(message);

    try
    {
        sysx.setMessage(sysxMsg, sysxMsg.length);
    } 
    catch (InvalidMidiDataException e)
    {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    out_queue.add(sysx);
}

The byteString is a string that contains the following hex message: F0411000004F1200020201070272F7 However, my control printout at the line textView.setText(message) returns the following string: 15410041000000715

Not quite sure where it goes wrong, shouldn't the textView message be the same as the input message?

Regards /M

I think it's your call substring(i*2, i*2 + 1). This will get the *first* hex digit of each pair. Shouldn't it be substring(i*2,i*2+2) ? — Joshua Davis, Mar 13 '14 at 21:48

score 0 · Accepted Answer · edited May 23 '17 at 12:04

I solved the problem by using this algorithm:

int len = s.length();
byte[] data = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
    data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                         + Character.digit(s.charAt(i+1), 16));

Provided in this discussion: Convert a string representation of a hex dump to a byte array using Java?

Not 100% certain about why my returned array is all jumbled, I guess the substring isn't quite up to the job for some reason.

Cheers /M

Sending a sysex message in Java

1 Answers1