How do I get Java to use the serial port in Linux?

Question

We make use of a java application that manages a pinpad via the serial port. This works perfectly on windows with the Sun Comm.jar, the supplied dll and the properties file.

Now we are attempting to use this solution on Linux (actually it does run on various other flavours of linux out in the field) - with Ubuntu server mode.

After much attempts - blood, sweat and almost tears we have this scenario:

Java version 1.4.2_17 Linux - Ubuntu Comm libs - Comm3 supplied by sun with the default driver specified

An external comm test shows the comm ports: /dev/ttyS0 and /dev/ttyS1 But the java application says unable to open port /dev/ttyS1

(using the RXRT files produces invalid port errors)

Has anyone been able to use java 1.4.2 on linux for serial port communication and found a solution that I could apply in my scenario?

greatly appreciated

Phill

Answer 1

It's been a while since I've done this. I remember that you can't just open /dev/ttyS0 as a file and I/O to it.

I remember having the same problem with Sun IO jars also.

The solution I remember settling on was to create a small command-line program in C that echoed stdin to the serial port and serial port in to stdout. Then, I launched this program from my java process. I don't have the code but there are lots of examples on the web for c programs that write to linux serial ports.

Answer 2

Make sure that you are using a user with permissions to access the serial ports. Some distributions put the serial ports in the uucp group, so make sure that the user belongs to that group.

Answer 3

We've been using the SerialIO libraries for Java serial communications on both Windows and Linux for several years now with great results (and no, I don't work for them :-)):

http://serialio.com/products/serialport/serialport.php

The libraries do not autodetect the available serial ports on Linux though - you have to manually configure them.

Answer 4

We did not change much, nothing in the libraries used. but removing the use of an EventListener on the serial port object fixed the problem.

This actually allowed for our code to work on linux (jre1.4.2, slackware and Suns Comm3 drivers) where this was not a problem on windows - strange.

Phill