Develop Reference

Sending a String through socket. Server not receiving it

I've been struggling lately to find a way to deliver strings through a socket file. I'm planning to create a remote tool(client) to execute things based on the received message(server).
I've searched answers for my problem on google and i found some things and managed to understand things but I also got some problems (i'm new to programming, not yet in college).
I would appreciate any help in this matter
SocketService.java ---- class file = serverside
package socket;
import java.io.DataInputStream;
import java.io.EOFException;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.TimeUnit;
public class ServiceSocket {
static ServerSocket myService;
static Socket thesocket;
static Thread socketThread;
public static boolean socketRunning;
public static DataInputStream socketMessage;
public static void initialise(String localhost, int portNumber ){
// make a server socket//////
try {
myService = new ServerSocket(portNumber);
System.out.println();
} catch (IOException e) {
e.printStackTrace();
}
//////////////////////////////
}
public static void deploySocket(){
socketThread = new Thread() {
public void run(){
// making connection
System.out.println("VVaiting for connection...");
try {
thesocket = myService.accept();
System.out.println("Connection made");
socketRunning = true;
} catch (IOException e) {
e.printStackTrace();
}
////////////////////////////////////
try {
StartBrain();
} catch (IOException e1) {
e1.printStackTrace();
}
if(socketRunning = false) {
try {
thesocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
};
socketThread.start();
}
public static String getSocketMessage() throws IOException {
try {
socketMessage = new DataInputStream(thesocket.getInputStream());
} catch (IOException e1) {
e1.printStackTrace();
}
boolean looprunning = true;
String message = null;
System.out.println("entering loop");
do {
try {
while (socketMessage.readUTF() != null) {
message = socketMessage.readUTF();
looprunning = false;
}
} catch (EOFException e) {
}
}while(looprunning);
System.out.println("Message received from UTF: " + message);
System.out.println("loop exited vvith message");
if(message == null) {
message = "no message";
}
return message;
}
public static void StartBrain() throws IOException {
System.out.println("socket brain started");
String BrainMessage = getSocketMessage();
if(BrainMessage == "command") {
System.out.println("Command EXECUTED HAHA");
} else if(BrainMessage == "taskschedule") {
System.out.println("task scheduled");
} else {
System.out.println("no command received");
}
}
Main.java ----- class file = serverside
package main;
import socket.ServiceSocket;
public class Main {
public static void main(String[] args) {
ServiceSocket.initialise("localhost", 3535);
ServiceSocket.deploySocket();
}
}
}
Main.java = CLIENT
package mainPackage;
import java.io.*;
import java.net.*;
import java.util.concurrent.TimeUnit;
public class Main {
private static Socket clientSocket;
public static void sendMessage(String message) throws IOException, InterruptedException {
DataOutputStream dOut = new DataOutputStream(Main.clientSocket.getOutputStream());
dOut.writeUTF(message);
dOut.flush();
dOut.close();
}
public static void main(String[] args) throws Exception {
// String modifiedSentence;
clientSocket = new Socket("localhost", 3535);
System.out.println("Initializing");
sendMessage("command");
boolean running = true;
while(running) {
TimeUnit.SECONDS.sleep(3);
sendMessage("taskschedule");
}
clientSocket.close();
}
}
main problem
do {
try {
while (socketMessage.readUTF() != null) {
message = socketMessage.readUTF();
looprunning = false;
}
} catch (EOFException e) {
}
}while(looprunning);
it doesn't read the string/UTF

It does read it, here:
while (socketMessage.readUTF() != null) {
and then throws it away as you're not assigning the return-value to a variable, and then tries to read another one, here:
message = socketMessage.readUTF();
but the one (first) message you send is already gone.

You have problem in
while (socketMessage.readUTF() != null) {
message = socketMessage.readUTF();
looprunning = false;
}
First call to method readUTF() will block thread and read UTF string from socket, but you discard this value and try read string second time.
If you replace socketMessage.readUTF() != null with looprunning server will log this messages:
VVaiting for connection...
Connection made
socket brain started
entering loop
Message received from UTF: command
loop exited vvith message
no command received
P.S.
Command is not recognized because use compare objects (string is object) with ==, but you must use equals.
public static void StartBrain() throws IOException {
System.out.println("socket brain started");
String BrainMessage = getSocketMessage();
if (BrainMessage.equals("command")) {
System.out.println("Command EXECUTED HAHA");
} else if (BrainMessage.equals("taskschedule")) {
System.out.println("task scheduled");
} else {
System.out.println("no command received");
}
}
Server log:
VVaiting for connection...
Connection made
socket brain started
entering loop
Message received from UTF: command
loop exited vvith message
Command EXECUTED HAHA

Java Socket ] instance of DataInputStream is print continue null

I'm making Chatting-Room program using the Java Swing.
In the client side, I was saw that doesn't read message from the server side.
The writeUTF() method of the client side is very well and I'm checked readUTF and writeUTF on the server side, that was very well too.
I think the problem is code which does as "Receiver" on the client side.
In the run() method of Thread, The instance dis of the DataInputStream has continuously null value.
I'm so confusing.. Please give me some help.
The bellow is part of my client&server code.
Thanks!
Client code
RoomBackground.java
public class RoomBackground {
private static String socket_server = "127.0.0.1";
private static Socket chatSocket;
private static DataOutputStream dos;
private static DataInputStream dis;
private ChatReceiver chatReceiver;
public Socket getChatSocket() {
return chatSocket;
}
public static DataOutputStream getDos() {
return dos;
}
public RoomBackground() throws IOException {
chatSocket = new Socket(socket_server, 7777);
chatReceiver = new ChatReceiver();
chatReceiver.start();
dos = new DataOutputStream(chatSocket.getOutputStream());
dis = new DataInputStream(chatSocket.getInputStream());
dos.writeUTF(User.getUser().getUsername());
dos.flush();
}
class ChatReceiver extends Thread {
#Override
public void run(){
try {
# PROBLEM CODE..... Allways "dis is null"
System.out.println("dis is " + dis);
# This line never executed.
while(dis != null) {
# some codes.....
}
} catch (IOException e) {
e.printStackTrace();
System.out.println(e.toString());
} catch (BadLocationException e) {
e.printStackTrace();
}
}
}
}
RoomFrame.java
public class RoomFrame extends JFrame{
private RoomBackground roomBackground;
public RoomFrame(int roomId) throws IOException {
chatField.addActionListener(new ActionListener() {
roomBackground = new RoomBackground();
#Override
public void actionPerformed(ActionEvent e) {
String msg = chatField.getText() + "\n";
try {
RoomBackground.getDos().writeUTF(msg);
# It works.
System.out.println("sent msg is " + msg);
} catch (IOException e1) {
e1.printStackTrace();
}
chatField.setText("");
}
});
}
}
Now server code.
Server Background.java
public class ChatReceiver extends Thread {
private DataInputStream in;
private DataOutputStream out;
public ChatReceiver(Socket chatSocket) throws IOException {
out = new DataOutputStream(chatSocket.getOutputStream());
in = new DataInputStream(chatSocket.getInputStream());
nick = in.readUTF();
addChatClient(nick, out);
}
#Override
public void run() {
try {
while(in!=null) {
chatMsg = in.readUTF();
# It works !
System.out.println("before send" + chatMsg);
sendMsg(chatMsg);
# It works too!
System.out.println("after send" + chatMsg);
}
}catch (IOException e) {
removeChatClient(nick);
}
}
}

When you are starting the ChatReceiver thread in the RoomBackground the dis object is not initialized yet, that is why it is null. One solution could be to initialize the dis variable in the ChatReceiver constructor.

chat in java not synchronized (sockets, threads)

I'm trying to figure out a way to get an instance of a server to negotiate between two clients by creating a chat thread between them.
I created this project, and it "almost" works... but it seems like there is a buffer of synch problem.
when writing a line in one side (i.e Client#1), it doesn't pass to the other side (i.e Client#2), but only after Client#2 trys to pass a line too.
I know there might be better ways to implement this, but I'd like to understand what's wrong with my code.
your help would be great!
the code:
server
import java.io.*;
import java.net.*;
public class Server
{
public static void main(String[] args)
{
int id = 1;
System.out.println();
System.out.println("Server");
try
{
ServerSocket serverSocket = new ServerSocket(4321);
while (true)
{
Socket client1Socket = serverSocket.accept();
Socket client2Socket = serverSocket.accept();
System.out.println("clients connected from ports: \n"
+ client1Socket.getPort() + ", " + client2Socket.getPort());
Thread client1Thread = new ServerThread(client1Socket, client2Socket, id);
client1Thread.start();
id++;
Thread client2Thread = new ServerThread(client2Socket, client1Socket, id);
client2Thread.start();
id++;
}
}
catch (IOException ioe)
{
ioe.printStackTrace();
}
}
}
server thread
import java.io.*;
import java.net.*;
import java.util.*;
public class ServerThread extends Thread
{
Socket sourceSocket;
Socket destSocket;
int id;
public ServerThread(Socket src, Socket dst, int n)
{
sourceSocket = src;
destSocket = dst;
id = n;
}
public void run()
{
try
{
Scanner clientInput = new Scanner(sourceSocket.getInputStream());
PrintStream destOutput = new PrintStream(destSocket.getOutputStream());
destOutput.println("You are chatting with Client " + id);
boolean more = true;
while (more)
{
String input = clientInput.nextLine();
destOutput.println(input);
if (input.equals("Q"))
{
more = false;
}
}
sourceSocket.close();
destSocket.close();
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}
client
import java.io.*;
import java.net.*;
import java.util.*;
public class Client
{
public static void main(String[] args)
{
System.out.println();
System.out.println("Client");
try
{
Socket clientSocket = new Socket("localhost", 4321);
System.out.println("Connection Established");
Scanner input = new Scanner(clientSocket.getInputStream());
PrintStream output = new PrintStream(clientSocket.getOutputStream());
Scanner in = new Scanner(System.in);
System.out.println(input.nextLine());
boolean more = true;
while (more)
{
String text = in.nextLine();
output.println(text);
String nextInput = input.nextLine();
if (nextInput == null)
{
more = false;
}
else
{
System.out.println(nextInput);
}
}
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}

In your client code, the line String text = in.nextLine(); will block your thread. That means if you never type in anything in your client, you can not receive anything. So the solution is to put your message receiving code in another thread. such as:
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
while (!Thread.interrupted()) {
System.out.println(input.nextLine());
}
}
});
thread.start();
while (true)
{
String text = in.nextLine();
output.println(text);
// String nextInput = input.nextLine();
......................
}

Program won't continue after initializing input/output streams?

Before people suspect that I have no idea what I'm doing at all (and end up voting this down for no reason at all), please read this:
It connects to my server just fine! I'm getting no errors (from the client OR server), and my server is recognizing the connection. It works with my friend's client that he made, but I wanted to make my own client, and apparently I'm doing something wrong. PLEASE STAY ON TOPIC! Thanks :)
Title basically says it all. I've tested with println messages above and below the setupStream() in my Client.java run(), but only the message above the setupStream() prints. I'm not sure how I'm supposed to initialize my stream without making my program come to a halt.
Client.java
import java.io.IOException;
public class Client extends Stream implements Runnable {
public boolean running = false;
private Thread clientThread;
Frame frame;
public Client() {
super("localhost", 43594);
frame = new ClientFrame(500, 500);
start();
}
public synchronized void start() {
if(running) return;
running = true;
clientThread = new Thread(this);
clientThread.start();
}
public synchronized void stop() {
if(!running) return;
running = false;
clientThread.interrupt();
try {
clientThread.join();
} catch (InterruptedException e) {e.printStackTrace();}
}
public void run() {
try{
setupStream();
while(running) {
System.out.println("running");
}
}catch(IOException e) {
e.printStackTrace();
}finally {
try{
out.close();
in.close();
socket.close();
clientThread.join();
}catch(IOException | InterruptedException e) { e.printStackTrace(); }
}
}
public static void main(String[] args) {
new Client();
}
}
Stream.java
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
public class Stream {
Socket socket;
ObjectOutputStream out;
ObjectInputStream in;
String data;
public Stream(String host, int port) {
try {
socket = new Socket(host, port);
} catch (IOException e) {
e.printStackTrace();
}
}
protected void setupStream() throws IOException {
out = new ObjectOutputStream(socket.getOutputStream());
out.flush();
in = new ObjectInputStream(socket.getInputStream());
}
}
My Server Thread:
package Server;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
public class User extends Thread {
public static int users = 0;
public int ID;
public String username;
boolean online = false;
public static ArrayList<String> usernames = new ArrayList<String>();
Socket socket;
DataOutputStream out;
DataInputStream in;
String input;
public User(Socket socket) {
this.socket = socket;
}
public String decode(String input) {
String[] split = input.split(" ");
if(input.startsWith("::")) {
try {
switch(split[0].substring(2, split[0].length()).toLowerCase()) {
case "setname":
case "changename":
case "newname":
if(usernames.contains(split[1].toLowerCase())) {
out.writeUTF("This name is already taken! Please choose a different one.");
out.flush();
return null;
}
if(username == null) {
username = split[1].substring(0, 1).toUpperCase() + split[1].substring(1, split[1].length());
Server.users.put(split[1].toLowerCase(), Server.user[ID]);
usernames.add(split[1].toLowerCase());
} else {
usernames.remove(username.toLowerCase());
username = split[1].substring(0, 1).toUpperCase() + split[1].substring(1, split[1].length());
usernames.add(split[1].toLowerCase());
}
return null;
case "rank+":
return null;
case "[sm]=":
return null;
}
}catch(IOException e) { }
}
return input;
}
String timeStamp;
public void run() {
try {
out = new DataOutputStream(socket.getOutputStream());
out.flush();
in = new DataInputStream(socket.getInputStream());
while((input = in.readUTF()) != null) {
input = decode(input);
if(input != null) {
if(username != null) {
timeStamp = new SimpleDateFormat("[h:mm:ss] ").format(Calendar.getInstance().getTime());
Server.sendGlobalMessage(timeStamp + username +": "+input);
} else {
timeStamp = new SimpleDateFormat("[h:mm:ss] ").format(Calendar.getInstance().getTime());
Server.sendGlobalMessage(timeStamp + "Guest "+ID+": "+input);
}
}
}
}catch(IOException e) { e.printStackTrace(); } finally {
try{
out.close();
in.close();
socket.close();
} catch(IOException e) { e.printStackTrace(); }
}
}
}
I haven't touched the code of my Server Thread for a while, since it has always worked up until I made my new client.

I suspect that your server does not create an ObjectOutputStream, so when the client constructs its ObjectInputStream, it blocks waiting for the object stream header, which never arrives.

Socket server build issue

The socket server listed in step 3 from http://pirate.shu.edu/~wachsmut/Teaching/CSAS2214/Virtual/Lectures/chat-client-server.html builds cleanly (java version "1.7.0_02") and runs without error but it exits without error instead of waiting to accept clients.
Updated ChatServer with missing arg code:
ChatServer:
import java.net.*;
import java.io.*;
public class ChatServer implements Runnable
{ private ServerSocket server = null;
private Thread thread = null;
private ChatServerThread client = null;
public ChatServer(int port)
{ try
{ System.out.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
start();
}
catch(IOException ioe)
{ System.out.println(ioe); }
}
public void run()
{ while (thread != null)
{ try
{ System.out.println("Waiting for a client ...");
addThread(server.accept());
}
catch(IOException ie)
{ System.out.println("Acceptance Error: " + ie); }
}
}
public void addThread(Socket socket)
{ System.out.println("Client accepted: " + socket);
client = new ChatServerThread(this, socket);
try
{ client.open();
client.start();
}
catch(IOException ioe)
{ System.out.println("Error opening thread: " + ioe); }
}
public void start() {
thread = new Thread(this);
thread.start();
}
public void stop() { /* no change */ }
public static void main(String args[]) {
ChatServer server = null;
if (args.length != 1)
System.out.println("Usage: java ChatServer port");
else
server = new ChatServer(Integer.parseInt(args[0]));
}
}
ChatServerThread:
import java.net.*;
import java.io.*;
public class ChatServerThread extends Thread
{ private Socket socket = null;
private ChatServer server = null;
private int ID = -1;
private DataInputStream streamIn = null;
public ChatServerThread(ChatServer _server, Socket _socket)
{ server = _server; socket = _socket; ID = socket.getPort();
}
public void run()
{ System.out.println("Server Thread " + ID + " running.");
while (true)
{ try
{ System.out.println(streamIn.readUTF());
}
catch(IOException ioe) {
System.out.println(ioe.getMessage());
}
}
}
public void open() throws IOException
{ streamIn = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
}
public void close() throws IOException
{ if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
}
}

EDIT: Updating my answer with a working solution.
Change these methods in your ChatServer class in order to be like these
public void start() {
thread = new Thread(this);
thread.start();
}
public void stop() {
// You should implement this too
}
public static void main(String args[]) {
// Instantiate a CharServer with the listening port 9191
ChatServer chatServer = new ChatServer(9191);
// CharServer.start() should not be confused with Thread.start();
// This calls our custom method up above, which includes a call to
// Thread(ChatServer).start();
chatServer.start();
}
Where 9191 is a port number I made up.
Executing CharServer#main method produces the following output and stays alive
Binding to port 9191, please wait ...
Server started: ServerSocket[addr=0.0.0.0/0.0.0.0,port=0,localport=9191]
Waiting for a client ...
Waiting for a client ...
You should also implement stop() method for the sake of functionality.

{ while (thread != null)
You never set thread so it will all be null
And you never create a thread
Try changing start() to:
public void start() {
thread = new Thread(this);
thread.start();
}