接口: javax.microedition.io.CommConnection，扩展了StreamConnection
BNF:
url ::== "comm:" port_id *(option_list)
port_id ::== 1*(characters)
option_list ::== *(baudrate | bitsperchar | stopbits | parity | blocking
| autocts | autorts)
baudrate ::== ";baudrate=" digits
bitsperchar ::== ";bitsperchar=" bit_value
bit_value ::== "7" | "8"
stopbits ::== ";stopbits=" stop_value
stop_value ::== "1" | "2"
parity ::== ";parity=" parity_value
parity_value ::== "even" | "odd" | "none"
blocking ::== ";blocking=" on_off
autocts ::== ";autocts=" on_off
autorts ::== ";autorts=" on_off
on_off ::== "on" | "off"
