Question

I am trying to write a program that will send GPS coordinates using telnet.
I keep getting the following exception:

Exception in thread "Timer-0" java.lang.NullPointerException
at org.apache.commons.net.telnet.Telnet._sendByte(Telnet.java:1060)
at org.apache.commons.net.telnet.TelnetOutputStream.write(TelnetOutputStream.java:87)
at org.apache.commons.net.io.ToNetASCIIOutputStream.write(ToNetASCIIOutputStream.java:77)
at org.apache.commons.net.io.ToNetASCIIOutputStream.write(ToNetASCIIOutputStream.java:111)
at java.io.PrintStream.write(PrintStream.java:430)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)
at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:85)
at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:168)
at java.io.PrintStream.write(PrintStream.java:477)
at java.io.PrintStream.print(PrintStream.java:619)
at java.io.PrintStream.println(PrintStream.java:756)
at com.example.myandroid.gpsSender$1.run(gpsSender.java:34)
at java.util.TimerThread.mainLoop(Timer.java:512)
at java.util.TimerThread.run(Timer.java:462)

I don’t know why I am getting this. Can you please tell me? thanks
Here is my code:

package com.example.myandroid;

import org.apache.commons.net.telnet.TelnetClient;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintStream;
import java.net.SocketException;
import java.util.Timer;
import java.util.TimerTask;

public class gpsSender {
    private TelnetClient telnet = new TelnetClient();

    public static void main(String[] args) throws Exception {
        gpsSender client = new gpsSender();
        client.start();
    }

    public String start() throws Exception {

        // Connect to the specified server

        telnet.connect("localhost", 5554);

        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            float longitude = 1;
            float latitude = 1;
            int count = 0;
            PrintStream out = new PrintStream(telnet.getOutputStream());

            public void run() {
                out.println("geo fix " + String.valueOf(longitude) + " "
                        + String.valueOf(latitude));
                out.flush();
                System.out.println("geo fix " + String.valueOf(longitude) + " "
                        + String.valueOf(latitude));
                longitude++;
                latitude++;
                count++;
                if (count > 1000) {
                    cancel();
                }
            }
        }, 0, 1000);
        try {
            telnet.disconnect();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return ("Done");
    }

    public void write(String value) {
        try {

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

}

Answer 1

The line

 telnet.disconnect();

is going to execute, so you won’t have an output stream to write to, hence the NPE. You should remove that line.