Develop Reference

How can I get the data from a thread that acts as a UDP server?

I am making an Android application that receives messages from an Arduino, I implemented a UDP server opening a Thread, but I can not get the value of the answer string "lastMessage", because with this value I will make a series of actions.
This is my class served_UDP:
public class Servidor_UDP {
private boolean server_activado = true;
private String lastMessage = "";
DatagramSocket socket;
private byte[] resp;
private DatagramPacket pqtResp;
Servidor_UDP()
{
resp = new byte[1024];
try {
socket = new DatagramSocket(6000);
pqtResp = new DatagramPacket(resp, resp.length);
} catch (SocketException e) {
e.printStackTrace();
}
}
public void start(){
Thread t = new Thread(new server());
t.start();
}
public class server implements Runnable {
server() { run(); }
public void run() {
String message = "";
try {
do
{
socket.receive(pqtResp);
//message = new String(resp).trim();
message = new String(pqtResp.getData(),0,pqtResp.getLength());
lastMessage = message;
} while(server_activado);
} catch (Exception e) {
e.printStackTrace();
}
}
}
public String getString()
{
return lastMessage;
}
public void setServer(boolean b)
{
server_activado = b;
}
}
This class I implemented from the onCreate of my MainActivity:
Servidor_UDP UDP_S;
UDP_S = new Servidor_UDP();
UDP_S.start();
I try to get the results of a method of the main class and show them in a TextView to make sure that the messages are arriving but it does not show me anything, just empty.
public void actualizarUI()
{
respuesta = UDP_S.getString();
txt.setText(respuesta);
}
I await your help, thanks in advance.

Your server() constructor should not call run(). Thread.start() will do that. At present Thread.start() is never executing, let alone completing, so any code that calls your start() method will never return.

EDIT: The other answer is right!
Ok so, I think you have the problem when creating the new server()...
You could try this:
private server server;
public void start(){
server = new server();
Thread t = new Thread(server);
t.start();
}
public class server implements Runnable {
server() { /*NO run();*/ }
public void run() {
String message = "";
try {
do
{
socket.receive(pqtResp);
//message = new String(resp).trim();
message = new String(pqtResp.getData(),0,pqtResp.getLength());
lastMessage = message;
} while(server_activado);
} catch (Exception e) {
e.printStackTrace();
}
}
public String getLastMessage() {
return lastMessage;
}
}
public String getString()
{
return server.getLastMessage();
}
You are doing new server(); so I you are creating a new object, you should save it in a class variable like I did, and then create a get method in the server class...
PD: Intenta no hacer codigo en castellano :)

Thread's while (true) loop only running once

I have a class that implements Runnable, and I start it's own thread in another method that runs when the window opens, however the while loop I have in the Runnable method only runs once, I know this because it displays the output only once. This is the code below.
static private final int SOCKET = 2222;
static JFrame frame = new JFrame();
static private ServerSocket serverSocket;
static private Socket socket;
static private DataOutputStream out;
static private DataInputStream in;
static private ArrayList<User> users = new ArrayList<>();
static private int logged = -1;
public GameServer() {
initComponents();
}
public void runServer() {
Thread server = new Thread(new StartServer());
server.start();
}
public void addUser(int logged, Socket socket, JTextArea taOut) {
users.add(logged, new User(socket, taOut, this, logged));
Thread thread = new Thread(users.get(logged));
thread.start();
}
public void removeUser(int index, Socket socket) {
users.remove(index);
updateIndexes();
try {
socket.close();
} catch (Exception e) {
taOut.append("Failed to close connection to user.\n");
}
}
public void updateIndexes() {
for (int i = 0; i == users.size()+1; i++) users.get(i).lowerIndex();
logged--;
}
public class StartServer implements Runnable {
#Override
public void run() {
taOut.append("Attempting to start server.\n");
try {
serverSocket = new ServerSocket(SOCKET);
} catch (Exception e) {
taOut.append("Port "+SOCKET+" is in use.\n");
return; // Prevent any further code from executing
}
taOut.append("Server started successfully.\n");
while (true) {
try {
taOut.append("Waiting for user...\n");
socket = serverSocket.accept(); // Wait for user to connect
logged++;
addUser(logged, socket, taOut);
taOut.append("Login request from: "+socket.getInetAddress()+"\n");
} catch (Exception e) {
taOut.append("There was an error with a user trying to connect.\n");
}
break;
}
}
}
private void formWindowOpened(java.awt.event.WindowEvent evt) {
runServer();
}

The body of the loop ends with a break; that terminates the loop. Just remove it and you should be fine.

send a message to specific client threads

I have this Server class,
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
public class Server {
public static ArrayList<String> waiting = new ArrayList<String>();
public static ArrayList<String> playing = new ArrayList<String>();
public static ArrayList<Integer> score = new ArrayList<Integer>();
public static void main(String[] args) {
try {
ServerSocket server = new ServerSocket(4321);
while (true) {
try {
Socket socket = server.accept();
new EchoThread(socket).start();
} catch (Exception exc) {
exc.printStackTrace();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
public void addClient(String name) {
waiting.add(name);
}
public int getNumClients() {
return waiting.size();
}
public String getClientName(int i) {
return waiting.get(i);
}
public void play() {
int scr = 0;
for (int i = 0; i < 4; i++) {
playing.add(waiting.get(0));
score.add(scr);
waiting.remove(0);
}
}
public boolean checkIfPlaying(String name) {
if (playing.indexOf(name) >= 0) {
return true;
} else {
return false;
}
}
}
and the Thread Class,
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
public class EchoThread extends Thread {
protected Socket socket;
public EchoThread(Socket clientSocket) {
this.socket = clientSocket;
}
public void run() {
Server s = new Server();
DataInputStream in = null;
DataOutputStream out = null;
String line;
try {
in = new DataInputStream(socket.getInputStream());
out = new DataOutputStream(socket.getOutputStream());
} catch (IOException e) {
return;
}
while (true) {
try {
line = in.readLine();
String[] prot = line.split(":");
if (prot[0].equals("/login")) {
s.addClient(prot[1]);
} else if (prot[0].equals("/waiting")) {
if (s.checkIfPlaying(prot[1])) {
out.writeBytes("Playing" + "\r\n");
} else {
if (s.getNumClients() >= 4) {
s.play();
out.writeBytes("Playing" + "\r\n");
} else {
out.writeBytes(s.getNumClients() + "\r\n");
}
}
}
} catch (IOException e) {
e.printStackTrace();
return;
}
}
}
}
If the client connect to the server, the name of the client is stored in Server Class Array, waiting.
If the waiting clients is equals to 4, it will remove from the waiting array and put it in playing array.
I would like to make the server send message to the first 4 clients in playing array.
How can I do it?

For your Server Class, I would change your ArrayList< String > for waiting and playing to ArrayList< EchoThread >. This way your Server class is tracking each client object themselves instead of just their names. When you instantiate your EchoThread objects, I would pass the local server object to each EchoThread that way each object knows about the server that instantiated them.
Server Class
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
public class Server {
public ArrayList<EchoThread> waiting = new ArrayList<EchoThread>();
public ArrayList<EchoThread> playing = new ArrayList<EchoThread>();
public ArrayList<Integer> score = new ArrayList<Integer>();
public static void main(String[] args) {
try {
// Instantiate a single server object that you can pass into your connected clients
Server myServer = new Server();
ServerSocket server = new ServerSocket(4321);
while (true) {
try {
Socket socket = server.accept();
// Pass myServer into Echo Thread
new EchoThread(myServer, socket).start();
} catch (Exception exc) {
exc.printStackTrace();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
// Have to synchronize this since multiple clients could be adding to this list at the same time
public synchronized void addClient(EchoThread client) {
waiting.add(client);
}
public int getNumClients() {
return waiting.size();
}
public String getClientName(int i) {
return waiting.get(i).getCName();
}
public void play() {
int scr = 0;
for (int i = 0; i < 4; i++) {
EchoThread clientBeingMovedToPlaying = waiting.get(0);
playing.add(clientBeingMovedToPlaying);
score.add(scr);
waiting.remove(0);
// This will be a new method in your EchoThread class
clientBeingMovedToPlaying.SendServerPlayingMessage();
}
}
public boolean checkIfPlaying(String name) {
boolean isPlaying = false;
for(EchoThread client : playing) {
if (client.getName().contentEquals(name)) {
isPlaying = true;
break;
}
}
return isPlaying;
}
}
For your Echo Thread class, I would make your variables in your run method class variables so they can be used throughout the class
EchoThread Class
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
public class EchoThread extends Thread {
protected Socket socket;
protected Server s;
protected DataInputStream in;
protected DataOutputStream out;
protected String line;
protected String clientName;
// This way, each EchoThread object knows about the server
public EchoThread(Server theServer, Socket clientSocket) {
this.s = theServer;
this.socket = clientSocket;
}
public void run() {
try {
in = new DataInputStream(socket.getInputStream());
out = new DataOutputStream(socket.getOutputStream());
} catch (IOException e) {
return;
}
while (true) {
try {
line = in.readLine();
String[] prot = line.split(":");
if (prot[0].equals("/login")) {
// Original code
//s.addClient(prot[1]);
// New code
clientName = prot[1];
s.addClient(this);
} else if (prot[0].equals("/waiting")) {
if (s.checkIfPlaying(prot[1])) {
out.writeBytes("Playing" + "\r\n");
} else {
// You don't want multiple clients firing the play method, so you need to synchronize your server object
synchronized (s) {
if (s.getNumClients() >= 4) {
s.play();
out.writeBytes("Playing" + "\r\n");
} else {
out.writeBytes(s.getNumClients() + "\r\n");
}
}
}
}
} catch (IOException e) {
e.printStackTrace();
return;
}
}
}
public String getCName() {
return clientName;
}
public void SendServerPlayingMessage() {
if (out != null) {
// Send whatever message you want
}
}
}
I think this'll get you what your wanting... Forgive any syntax or logical errors, I don't have an IDE right in front of me at the moment.

converting mp3 to byte in java

I found this code for playing mp3 in java and I want to stream this in a network using UDP so I want to convert the mp3 file to byte so I can send it using DatagramPacket. What should I convert to do this?
I will be needing to send 60Kbyte of buffer to the datagrampacket.
import javazoom.jl.player.advanced.*;
public class JLayerTest
{
public static void main(String[] args)
{
SoundJLayer soundToPlay = new SoundJLayer("Test.mp3");
soundToPlay.play();
}
}
class SoundJLayer extends PlaybackListener implements Runnable
{
private String filePath;
private AdvancedPlayer player;
private Thread playerThread;
public SoundJLayer(String filePath)
{
this.filePath = filePath;
}
public void play()
{
try
{
String urlAsString = "file:\\C:\\Users\\Lorenz Kyle\\Desktop\\CODES by Lo\\Case 4\\Server\\Mp3MulticastServer\\src\\test.mp3";
this.player = new AdvancedPlayer
(
new java.net.URL(urlAsString).openStream(),
javazoom.jl.player.FactoryRegistry.systemRegistry().createAudioDevice()
);
this.player.setPlayBackListener(this);
this.playerThread = new Thread(this, "AudioPlayerThread");
this.playerThread.start();
}
catch (Exception ex)
{
}
}
// PlaybackListener members
public void playbackStarted(PlaybackEvent playbackEvent)
{
System.out.println("playbackStarted");
}
public void playbackFinished(PlaybackEvent playbackEvent)
{
System.out.println("playbackEnded");
}
// Runnable members
public void run()
{
try
{
this.player.play();
}
catch (javazoom.jl.decoder.JavaLayerException ex)
{
ex.printStackTrace();
}
}
}

Async Tcp Connection

I have a slight problem, I have a TCP class which connects to a server, transfers data then closes, this all works well except for if I connect, then stop it, it works, if I keep on doing this, it works, but on the fifth time the connection hangs without any error and doesn't transfer any data.. I've got no idea how to fix this... This is my TCP class code:
package com.millennium.isynccrm.Classes;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import android.os.AsyncTask;
import android.os.CountDownTimer;
import android.util.Log;
public class TcpClient {
public static boolean connected = false;
private static Socket socket;
private static boolean pause = false;
private static SyncClient syncClient = new SyncClient();
public static int sendCount = 0;
public static int receiveCount = 0;
private static AsyncTask<?, ?, ?> sendAsyncTask;
private static AsyncTask<?, ?, ?> receiveAsyncTask;
public TcpClient() { }
public void send (String line) {
if (!connected) connect();
while (!connected) { }
sendAsyncTask = new SenderThread().execute(line);
}
public void disconnect() {
try {
if(connected == true) {
socket.close();
connected = false;
sendCount = 0;
receiveCount = 0;
if (receiveAsyncTask.getStatus().name().equals("RUNNING")) {
receiveAsyncTask.cancel(true);
}
if (sendAsyncTask.getStatus().name().equals("RUNNING")) {
sendAsyncTask.cancel(true);
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void pauseReceivingForTimeInterval(int milliseconds) {
pause = true;
new CountDownTimer(milliseconds, 0) {
public void onTick(long millisUntilFinished) { }
public void onFinish() {
pause = false;
}
}.start();
}
private void connect() {
new Thread(new Runnable() {
public void run() {
try {
if (connected == false) {
socket = new Socket("192.168.1.1", 80);
connected = true;
sendCount = 0;
receiveCount = 0;
try {
if (receiveAsyncTask.getStatus().name().equals("FINISHED")) {
receiveAsyncTask = new RecieverThread().execute("");
} else if (receiveAsyncTask.getStatus().name().equals("RUNNING")) {
receiveAsyncTask.cancel(true);
receiveAsyncTask = new RecieverThread().execute("");
}
} catch (Exception e) { receiveAsyncTask = new RecieverThread().execute(""); }
}
} catch (UnknownHostException e) {
connected = false;
e.printStackTrace();
} catch (IOException e) {
connected = false;
e.printStackTrace();
}
}
}).start();
}
private static PrintWriter output;
private static BufferedReader input = null;
private class RecieverThread extends AsyncTask<String, Void, String> {
protected String doInBackground(String... line) {
while (pause) { }
try {
receiveCount++;
if (receiveCount == 1) input = new BufferedReader(new InputStreamReader(socket.getInputStream()), 8 * 1024);
return input.readLine();
} catch (IOException e) {
Log.d("error", "stop");
}
return "stop";
}
protected void onPostExecute(String result) {
if (result == null) return;
else if (!result.equals("") && !result.equals("stop")) syncClient.recieveMessage(result);
else if (!result.equals("stop")) receiveAsyncTask = new RecieverThread().execute("");
}
}
private class SenderThread extends AsyncTask<String, Void, String> {
protected String doInBackground(String... line) {
while (pause) { }
sendCount++;
if (sendCount == 1) {
try {
output = new PrintWriter(socket.getOutputStream(),true);
} catch(Exception e) { e.printStackTrace(); }
}
String msg = line[0] + "\r\n";
output.print(msg);
output.flush();
return "";
}
protected void onPostExecute(String result) {
}
}
}
As you can see another class sends a line to this class to send to the server, then a Async task sends it and another Async task receives it and passes it onto another class which processes it and so on. On the UI I have a start button which when is pressed turns into a stop button and when stop is pressed it calls the 'disconnect' function in here.
I'm not too sure wherever I have done my RecieverThread AsyncTask is correct, it waits for a line from the socket then passes it on and restarts it self to listen for another line, is this a 'good' way of doing this? Or is it a terrible way (which I imagine it is). To be honest I think this class is very 'messy' and I will more than likely be redoing it.
Any suggestion why I can never send data on the fifth time I connect to the server? (One last note, the server is not to blame here, as we have a iPhone app which does the same thing) (Extra side note.. I'm pretty new to Tcp connections and that sort of stuff, and new to Threading/Async Tasks.) :)
Any help, assistance would be much appreciated (: Thanks!

while (!connected) {}??? that's no way to do asynchronous anything. You are hogging the CPU waiting for something to happen, and preventing it from happening by hogging the CPU. Use a Selector, or do a blocking-mode connect.