Page 53 - The Definitive Guide to Building Java Robots

Preston_5564C02.fm Page 34 Wednesday, September 14, 2005 5:42 AM

34 CHAPTER 2 ■ SERIAL COMMUNICATION

than the standard serial port, and two, all of our implementing classes would not use this port—
they would instead need to use the connector to the WebSerialPort: the WebSerialClient.
The class WebSerialClient implements the interface JSerialPort, so now anything I write
can just use this interface and I can interchange the WebSerialClient, the StandardSerialPort,
or my own implementation and I will not have to modify any of the code that uses these. Pretty
slick, huh?
The first field in this class is a formatter object. I use this for debugging the milliseconds of
an operation. You will need to debug and experiment with different timeout values for items
connected to your microcontroller. Too long and you’ll be wasting performance, too little and
you’ll get nothing back or only junk. I’ll discuss more of this in Chapter 4, but it’s probably best
to make a note of it for now.
The string URL and the URL object will be used to connect to the webcom.jsp on my robot.
The dtr variable is set to false if I am connecting to a BASIC Stamp carrier board. The timeout
and MAX_DELAY are ints that will determine whether the client should wait for a return from
webcom.jsp, or whether it should just make two calls: one write and one read. I’ve found that
depending on your WiFi connection, you might want to increase or decrease this value.
Next, the construction of this client will take the string server that represents the server
name or IP address of the web server hosting the webcom.jsp. The string, tcpPort, represents
the port where the web server hosting the webcom.jsp is listening. (See Example 2-8.)

Example 2-8. WebSerialClient.java
package com.scottpreston.javarobot.chapter2;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.text.SimpleDateFormat;
import java.util.Date;

public class WebSerialClient implements JSerialPort {

private SimpleDateFormat formatter = new SimpleDateFormat(
"MM/dd/yy - HH:mm:ss.SSS");
private String url;
private URL myUrl;
private boolean dtr = false;
private int timeout = 0;
public static final int MAX_DELAY = 500;

public WebSerialClient(String server, String tcpPort, String portId) {
this.url = "http://" + server + ":" + tcpPort
+ "/" + WebSerialPort.COMM_JSP + "?portid=" + portId;
}