This is the Java Communications API. You can get it here but it won't help you. The supported platforms are Solaris SPARC, Solaris x86, and Linux x86.
For Mac and Linux, if the serial port is already configured, you can open /dev/ttyS0, /dev/ttyS1, /dev/ttyS2, etc. as a file and read/write to it. On Windows, if the serial port is already configured you can open "COM1", "COM2", etc. and read and write to it.
Unfortunately, javax.comm (as provided in the reference implementation) isn't cross-platform, so you'll have to either resort to bundling additional native libraries and supporting classes or use a platform-dependent way to configure the serial port. On Windows, this could be the "mode" command, and on Mac/Linux, this could be the stty command.
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