Reading and Writing: Lock Step
Problem
You want to read and write on a port, and your communications needs are simple.
Solution
Just use read and write calls.
Discussion
Suppose you need to send a command to a device and get a response
back, and then send another, and get another. This has been called a
“lock-step” protocol, since both ends of the
communication are locked into step with one another, like soldiers on
parade. There is no requirement that both ends be able to write at
the same time (see Recipes 10.7 and 10.8 for this), since you know
what the response to your command should be and don’t proceed
until you have received that response. A well-known example is using
a standard Hayes-command-set
modem to just dial a phone number.
In its simplest form, you send the command string ATZ and expect the
response OK, then send ATD with the number, and expect CONNECT. To
implement this, we first subclass from
CommPortOpen
to add two functions,
send
and expect
, which perform
reasonably obvious functions for dealing with
such devices. See Example 11-5.
Example 11-5. CommPortModem.java
import java.awt.*; import java.io.*; import javax.comm.*; import java.util.*; /** * Subclasses CommPortOpen and adds send/expect handling for dealing * with Hayes-type modems. * */ public class CommPortModem extends CommPortOpen { /** The last line read from the serial port. */ protected String response; /** A flag to control debugging output. */ protected boolean debug = true; public CommPortModem(Frame ...
Get Java Cookbook now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.