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HTTYR: Responding to phone events

This post is part of a series on how to train your robot.

The technique described here only works if you are using a Wifi dongle.

Suppose that you want your robot to know when you come home, so that it can greet you. Or you want it to come and tell you when you receive a text message. If you have an Android phone, you can use an application such as AutomateIt for this.

To let you know that you have come home, you just wake up the phone before you get to your door to make it connect to your Wifi.

AutomateIt lets you set up rules that fire when events occur. Those events can include your phone waking up, connecting to the Wifi network, disconnecting from the Wifi network, receiving a text, etc.. One of the actions that AutomateIt supports is to connect to a web page in the background (without starting a browser). So, if we had a simple web server on our EV3 robot, we could get our Android phone to tell it about all sort of events, and the robot could respond appropriately.

It does not need to be a very complex web server. It only needs to respond to GET commands, and it can deal with them one at a time.

The URLs that you type into AutomateIt will look like




So here is a very simple web server that will do the job:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;

import lejos.hardware.Sound;

public class SimpleWebServer {
  public static final int PORT = 80;
  private ServerSocket ss;
  private Socket sock;

  public SimpleWebServer() throws IOException {
    ss = new ServerSocket(PORT);

  public void run() throws IOException {
    for (;;) {
      sock = ss.accept();
      InputStream is = sock.getInputStream();
      OutputStream os = sock.getOutputStream();

      BufferedReader br = new BufferedReader(new InputStreamReader(is));
      PrintStream ps = new PrintStream(os);

      for (;;) {
        String cmd = br.readLine();
        if (cmd == null)
        String reply = execute(cmd);
        if (reply != null)
        else {


  public String execute(String cmd) {
    System.out.println("cmd: " + cmd);
    String[] tokens = cmd.split(" ");

    if (tokens.length > 1 && tokens[0].equals("GET")) {
      if (tokens[1].equals("/Hello")) {
      } else if (tokens[1].equals("/Goodbye")) {
      } else if (tokens[1].equals("/Text")) {
      return "HTTP/1.1 200 OK\r\n\r\nOK\r\n";
    return null;

  public static void main(String[] args) throws IOException {
    new SimpleWebServer().run();


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