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How to use existing Objects in an overwritten run() Method?

I'm a beginner in programming and do strugle a bit.
So I'm building a TCP peer to peer Chat and that requires me to divide the tasks -> Threads.
So I want to built a Thread for the "writing" part of that connection (Scanner, DataOutputStream etc.) In order to do that i implemented Runnable and that forces me to write my Thread in the overwritten run() method.
Now I have a bit of a problem, because in Order to send my messages out to the "other end (another client) I need the "socket.getOutputStream" but I cant use it in the run() method and i dont know how to fix this problem, sitting already a week on this problem. Any ideas ?
public class ClientHorcher implements Runnable {
public static void main(String[] args) {
try {
ServerSocket serverSocket = new ServerSocket(11111);
System.out.println("Waiting For Connection:-");
Socket socket = serverSocket.accept();
Scanner scanner = new Scanner(System.in);
DataInputStream datenRein = new DataInputStream(socket.getInputStream());
DataOutputStream datenRaus = new DataOutputStream(socket.getOutputStream());
String nickname;
System.out.print("Gib einen Nickname ein: ");
nickname = scanner.nextLine();
while (true) {
String vonMsg = datenRein.readUTF(in);
System.out.println("Client:-" + vonMsg);
if (vonMsg.equals("exit")) {
System.out.println("Beenden!!!");
datenRein.close();
datenRaus.close();
scanner.close();
socket.close();
serverSocket.close();
System.exit(0);
}
System.out.print(nickname + ":-");
String zuMsg = scanner.nextLine();
datenRaus.writeUTF(zuMsg);
if (zuMsg.equals("exit")) {
System.out.println("Quiting!!!");
datenRein.close();
datenRaus.close();
scanner.close();
socket.close();
serverSocket.close();
System.exit(0);
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void run() {
}
}`
`public class ClientVerbinder implements Runnable {
public static void main(String[] args) {
try {
Socket socket = new Socket("Localhost", 11111);
System.out.println("Connected");
Scanner scanner = new Scanner(System.in);
DataInputStream datenRein = new DataInputStream(socket.getInputStream());
DataOutputStream datenRaus = new DataOutputStream(socket.getOutputStream());
String nickname;
System.out.print("Gib einen Nickname ein: ");
nickname = scanner.nextLine();
while (true) {
System.out.print(nickname+":-");
String zuMsg = scanner.nextLine();
datenRaus.writeUTF(zuMsg);
if (zuMsg.equals("exit")) {
System.out.println("Beenden!!!");
datenRein.close();
datenRaus.close();
scanner.close();
socket.close();
System.exit(0);
}
String vonMsg = datenRein.readUTF();
System.out.println("CLient"+":-" + vonMsg);
if (vonMsg.equals("exit")) {
System.out.println("Quiting!!!");
datenRein.close();
datenRaus.close();
scanner.close();
socket.close();
System.exit(0);
}
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
#Override
public void run() {
}
}

Multiple possibilities.
Use static variables. Normally you would not do that, but because your code is all-static, you could
Use member variables in an OO-style code.
If you wanted to do it properly, you'd split the server into two parts:
The ServerSocket listener that only listens to connections (Socket connectionToClient = ss.accept), and whenever a connection comes in, creates a new
ClientHandler, passes in the Socket, and the ClientHandler then starts its own thread internally
This way, the ClientHandler has all the data it needs (again as member variables) and can work on its own concerns (aka 'separation of concerns).
Update
This is what I created. Really simple.
Start Server
Start 1st client
Start 2nd client
In any client, type message
Other client receives it
Classes:
SimpleServer
package stackoverflow.simplemtserver;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.LinkedBlockingDeque;
public class SimpleServer { // make it closeable and close sockets if this is not standalone
public static void main(final String[] args) throws IOException {
final int port = 7623;
new SimpleServer(port);
}
final LinkedBlockingDeque<SimpleServerClientHandler> clientHandlers = new LinkedBlockingDeque<>();
private final ServerSocket mServerSocket;
public SimpleServer(final int pPort) throws IOException {
mServerSocket = new ServerSocket(pPort);
final Thread m = new Thread(() -> runLoop(), getClass().getSimpleName() + " Main Loop");
m.start();
}
private void runLoop() {
while (true) {
try {
System.out.println("Server waiting for connection...");
#SuppressWarnings("resource") final Socket cs = mServerSocket.accept(); // do NOT close the socket here, no try-resource, will interrupt threaded communication!
final SimpleServerClientHandler ch = new SimpleServerClientHandler(this, cs);
clientHandlers.add(ch);
System.out.println("Connection accepted, handler started. Handlers active: " + clientHandlers.size());
} catch (final IOException e) {
// handle this how you need it
e.printStackTrace();
}
}
}
public void signOffClientHandler(final SimpleServerClientHandler pClientHandler) {
clientHandlers.remove(pClientHandler); // we could also accommplish this using stack trace to avoid access from outside, but this is the easier solution
}
public void spreadMessageToClients(final String pMessageFromClient, final SimpleServerClientHandler pSimpleServerClientHandler) {
for (final SimpleServerClientHandler ch : clientHandlers) {
if (ch != pSimpleServerClientHandler) ch.relayMessageToClient(pMessageFromClient); // we can work with identity == and != here
}
}
}
SimpleServerClientHandler
package stackoverflow.simplemtserver;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
public class SimpleServerClientHandler {
private final SimpleServer mParentServer;
private final Socket mClientSocket;
private final DataInputStream mDIS;
private final DataOutputStream mDOS;
public SimpleServerClientHandler(final SimpleServer pSimpleServer, final Socket pCS) throws IOException {
mParentServer = pSimpleServer;
mClientSocket = pCS;
mDIS = new DataInputStream(mClientSocket.getInputStream());
mDOS = new DataOutputStream(mClientSocket.getOutputStream());
final Thread t = new Thread(() -> runComms(), getClass().getSimpleName() + " Comms Loop");
t.setDaemon(true); // threads now stop once server stops. this is NOT a soft exit
t.start();
}
private void runComms() {
try {
try {
while (true) {
// do all your logic here, work with DIS and DOS
final String messageFromClient = mDIS.readUTF();
if (messageFromClient == null) break;
if (!messageFromClient.startsWith("*")) mParentServer.spreadMessageToClients(messageFromClient, this);
}
} catch (final Exception e) {
// TODO: handle exception
}
} finally {
try {
mClientSocket.close(); // also closes DataIn/Out
} catch (final IOException e) { /* ignore */ }
mParentServer.signOffClientHandler(this);
}
}
public void relayMessageToClient(final String pMessageFromClient) {
try {
mDOS.writeUTF("*" + pMessageFromClient);
} catch (final IOException e) {
// ignore unless needed otherwise
}
}
}
SimpleClient
package stackoverflow.simplemtserver;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Scanner;
public class SimpleClient {
public static void main(final String[] args) throws UnknownHostException, IOException {
final String hostname = "localhost";
final int port = 7623;
try (final Socket s = new Socket(hostname, port);
final DataInputStream dis = new DataInputStream(s.getInputStream());
final DataOutputStream dos = new DataOutputStream(s.getOutputStream());
final Scanner scanner = new Scanner(System.in);) {
final Thread t = new Thread(() -> runListenerLoop(dis), SimpleClient.class.getSimpleName() + " Reader Thread");
t.setDaemon(true);
t.start();
while (true) {
System.out.println("Enter message:");
System.out.flush();
final String msg = scanner.nextLine();
if (msg == null) break;
System.out.println("Spreading message: " + msg);
dos.writeUTF(msg);
}
}
}
private static void runListenerLoop(final DataInputStream pDis) {
while (true) {
try {
System.out.println("Waiting for incoming messages...");
final String msg = pDis.readUTF();
System.out.println("Received: " + msg);
} catch (final SocketException e) {
// if ("java.net.SocketException: Connection reset".equals(e.getMessage()))
break;
} catch (final IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
From here on, there's now more ways you can extend this client/server communication:
use opcodes (read/write int constants or enums before data) to distinguish for special operations and/or messages (like this here puts an asterisk in front of the string to prevent re-re-laying the same message indefinitely over the network)
read multiple strings for user, message, additional options
implement this is a user friendly UI so you dont have to use console I/O
Update 2
The pure peer-to-peer solution is this one.
If the app is run without params, it goes into listening mode, waiting for a connection.
If the app is run with one arguments, it interprets it as listening port and also goes into listening mode.
If the app is un with [hostname] [port] arguments, it will try to connect there
Example:
start first app without arguments (listening)
start second app with arguments "localhost 7642" (connecting)
both apps will now
connect,
then set up I/O resources,
then start the listening thread for incoming messages
then go into the read-keyboard-and-write-to-socket loop
now you can type a message in one of the apps, the other one will receive it
p2p code:
package stackoverflow.simplemtserver;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.Scanner;
public class SimplePeerToPeerClient {
static public final int DEFAULT_PORT = 7642;
public static void main(final String[] args) throws UnknownHostException, IOException {
if (args.length == 0) {
System.out.println("Waiting on default port " + DEFAULT_PORT);
waitForConnection(DEFAULT_PORT);
} else if (args.length == 1) {
final int port = Integer.parseInt(args[0]);
System.out.println("Waiting on port " + port);
waitForConnection(port);
} else if (args.length == 2) {
final String hostName = args[0];
final int port = Integer.parseInt(args[1]);
System.out.println("Connecting to " + hostName + " on port " + port);
connectToOtherSide(hostName, port);
} else throw new IllegalArgumentException("Invalid amount of argument! Need none (listen) or 2: [hostname] [port] (connect)");
}
private static void waitForConnection(final int pPort) throws IOException {
try (final ServerSocket ss = new ServerSocket(pPort);) {
#SuppressWarnings("resource") final Socket socket = ss.accept(); // will get closed later
startComms(socket);
} // closes ServerSocket after 1st connection
}
private static void connectToOtherSide(final String pHostName, final int pPort) throws UnknownHostException, IOException {
#SuppressWarnings("resource") final Socket socket = new Socket(pHostName, pPort); // will get closed later
startComms(socket);
}
private static void startComms(final Socket pSocket) throws IOException {
try (
final DataInputStream dis = new DataInputStream(pSocket.getInputStream());
final DataOutputStream dos = new DataOutputStream(pSocket.getOutputStream());
final Scanner scanner = new Scanner(System.in);) {
// run the listener loop
final Thread t = new Thread(() -> runListenerLoop(dis), SimpleClient.class.getSimpleName() + " Reader Thread");
t.setDaemon(true);
t.start();
// run my keyboard-input-send loop
while (true) {
System.out.println("Enter message:");
System.out.flush();
final String msg = scanner.nextLine();
if (msg == null) break; // empty input ends client
System.out.println("Spreading message: " + msg);
dos.writeUTF(msg);
}
} finally {
try {
pSocket.close();
} catch (final IOException e) { /* ignore */ }
}
}
private static void runListenerLoop(final DataInputStream pDis) {
while (true) {
try {
System.out.println("Waiting for incoming messages...");
final String msg = pDis.readUTF();
System.out.println("Received: " + msg);
} catch (final SocketException e) {
// if ("java.net.SocketException: Connection reset".equals(e.getMessage()))
break;
} catch (final IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

Server doesn't forward message to all in the chat

i am trying to create a simple chat app using java sockets, the server is threaded, when a client connects its socket is added to an ArrayList, so that i can send to all in that list.
the problem is when 3 clients are connected, the for loop that sends doesn't work properly, for ex : client 0 sends to both 1 and 2 but client 2 doesn't send to anyone :(
The server and the ClientHandler :
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Scanner;
public class MainServer {
private static int portnumber = 6968;
static ArrayList <ClientHandler> allClients = new ArrayList<>();
public static void main(String[] args) throws Exception {
// init
// server works by default on localhost
ServerSocket serversocket = new ServerSocket(portnumber);
int clientNo = 0;
System.out.println("server is running on port : " + portnumber);
while (true) {
// creating a socket for each connection
Socket clientsocket = null;
try {
// receiving incoming requests from users/clients
clientsocket = serversocket.accept();
// input and output from client
PrintWriter out = new PrintWriter(clientsocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(clientsocket.getInputStream()));
// create a threads
ClientHandler ch = new ClientHandler(clientsocket, "Client#" + clientNo, in, out);
// adding to the clientList
allClients.add(ch);
System.out.println(ch.clientName + " has joined");
Thread clientThread = new Thread(ch);
clientThread.start();
// decrease when user leaves
clientNo++;
} catch (Exception e) {
clientsocket.close();
e.printStackTrace();
System.exit(1);
//out.close();
//in.close();
//clientSocket.close();
//serverSocket.close();
}
}
}
}
// handle client requests
public class ClientHandler implements Runnable{
public String clientName;
public Socket clientsocket = null;
public boolean active = false;
private BufferedReader inp;
private PrintWriter out;
private final String EXIT_STR = "exit";
public Scanner clientSc = new Scanner(System.in);
public ClientHandler(Socket socket, String name, BufferedReader inp, PrintWriter out) {
this.clientsocket = socket;
this.clientName = name;
this.inp = inp;
this.out = out;
// active when the thread is created
this.active = true;
}
#Override
public void run() {
// getting the output temp
String recivedMsg = "";
while (true) {
try {
recivedMsg = inp.readLine();
System.out.println(recivedMsg);
// check for ctrl+C
if (recivedMsg.equals(this.EXIT_STR)){
// send to all
System.out.println(this.clientName + " exits");
// close the connection and break
this.active = false;
this.clientsocket.close();
// bye
break;
}
// send to all except me
for (ClientHandler client : MainServer.allClients){
if (!client.clientName.equals(this.clientName)){
client.out.println(this.clientName + ":" + recivedMsg);
client.out.flush();
break;
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
try {
// clean
this.clientsocket.close();
this.inp.close();
this.out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
The client :
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
public class Client {
private String hostName;
private int portNumber;
// set connction and server
public PrintWriter out = null;
public BufferedReader in = null;
public Socket clientSocket = null;
Client(String hostName, int port) {
this.hostName = hostName;
this.portNumber = port;
// setting the connction
this.setConnection();
}
private void setConnection () {
try {
this.clientSocket = new Socket(this.hostName, this.portNumber);
this.out = new PrintWriter(this.clientSocket.getOutputStream(), true);
this.in = new BufferedReader(new InputStreamReader(this.clientSocket.getInputStream()));
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
public void sendMessageToServer(String msg) {
//System.out.println("The msg is : " + msg);
out.println(msg);
}
public String readMessage() {
String outputMsg = "";
try {
outputMsg = in.readLine();
} catch (IOException e) {
e.printStackTrace();
}
return outputMsg;
}
// shit cleaning
public void closeSession(){
try {
this.out.close();
this.in.close();
this.clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
System.out.println("Session has been terminated!");
}
public static void main(String args[]) throws IOException{
// init
String host = "localhost";
int port = 6968;
Client newClient = new Client(host, port);
// // send a message
Scanner sc = new Scanner(System.in);
Thread sendMsg = new Thread(new Runnable() {
#Override
public void run() {
while (true) {
try {
String userInput = sc.nextLine();
newClient.sendMessageToServer(userInput);
if (userInput.equals("exit")) {
System.exit(1);
}
} catch (Exception e) {
System.exit(1);
}
}
}
});
Thread getMsg = new Thread(new Runnable() {
#Override
public void run() {
while (true) {
String msgRead = "";
try {
msgRead = newClient.readMessage();
System.out.println(msgRead);
} catch (Exception e) {
System.exit(1);
}
}
}
});
sendMsg.start();
getMsg.start();
}
}
I think the problem is here :
// send to all except me
for (ClientHandler client : MainServer.allClients){
if (!client.clientName.equals(this.clientName)){
client.out.println(this.clientName + ":" + recivedMsg);
client.out.flush();
break;
}
}

The fix is straightforward: remove the break statement from the loop where you think the problem is.
This break statement causes the loop through all the ClientHandlers to stop as soon as it sends the message to one client. You don't want this: you want this loop to keep going and send the message to all clients other than the one that wrote the message.

Java basic concurrent communicator - does not fully accept connection

I want to create simple communicator with one server and few clients who could connect and send data to it. It works fine without any threads, with only one client, but once i try to incorporate concurrency it doesn't work. From client perspective there is some connection, I can send data, but there is no sign of receiving that data on server. Here is the server class:
import java.io.*;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Random;
public class MyServerSocket implements Runnable
{
private ServerSocket serverSocket;
public MyServerSocket() throws Exception
{
Random generator = new Random();
this.serverSocket = new ServerSocket(generator.nextInt(65000 - 60000) + 60000, 50, InetAddress.getByName("192.168.0.105"));
}
public InetAddress getSocketIPAddress()
{
return this.serverSocket.getInetAddress();
}
public int getPort()
{
return this.serverSocket.getLocalPort();
}
public void run()
{
while (true)
{
System.out.println("Running a thread");
try
{
String data = null;
Socket client = this.serverSocket.accept();
String clientAddress = client.getInetAddress().getHostName();
System.out.println("Connection from: " + clientAddress);
System.out.println("Here I am");
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
String message = "";
while ((data = in.readLine()) != null && data.compareToIgnoreCase("quit") != 0)
{
message = ("\r\nMessage from " + clientAddress + ": " + data);
System.out.println(message);
out.write(message);
}
} catch (Exception e)
{
System.out.println("Something went wrong");
} finally
{
try
{
serverSocket.close();
} catch (IOException e)
{
e.printStackTrace();
}
}
}
}
}
Server main:
import java.lang.Thread;
public class Main
{
public static void main(String[] args)
{
try
{
MyServerSocket socket = new MyServerSocket();
Runnable runnable = new MyServerSocket();
System.out.println("Port number: " + socket.getPort() + " IP address: " + socket.getSocketIPAddress());
Thread thread = new Thread(runnable);
thread.start();
}catch (Exception e)
{
e.printStackTrace();
}
}
}
Client class:
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.util.Scanner;
public class ClientSocket
{
private Socket socket;
private Scanner scanner;
ClientSocket(InetAddress serverAddress, int serverPort) throws Exception
{
this.socket = new Socket(serverAddress, serverPort);
this.scanner = new Scanner(System.in);
}
public void sendData() throws Exception
{
String data;
System.out.println("Please type in the message. If you want to terminate the connection, type Quit");
PrintWriter out = new PrintWriter(this.socket.getOutputStream(), true);
do
{
data = scanner.nextLine();
out.println(data);
out.flush();
}while(data.compareToIgnoreCase("quit") != 0);
out.println();
}
}
Client main:
import java.net.InetAddress;
import java.util.Scanner;
public class Main
{
public static void main(String[] args)
{
Scanner scanner = new Scanner(System.in);
int port;
System.out.println("Provide port at which you will communicate with the server");
port = scanner.nextInt();
try
{
ClientSocket socket1 = new ClientSocket(InetAddress.getByName("192.168.0.105"), port);
socket1.sendData();
}catch(Exception e)
{
System.out.println("Could not connect to the server.");
}
}
}
Server somehow stops its working when is about to accept the client connection, while client works fine and seem to be connected to the server.

In server side, once you accept a client connection, you should new a thread to process this connection:
import java.io.*;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Random;
public class MyServerSocket implements Runnable {
private ServerSocket serverSocket;
public MyServerSocket() throws Exception {
Random generator = new Random();
this.serverSocket = new ServerSocket(generator.nextInt(65000 - 60000) + 60000, 50, InetAddress.getByName("192.168.0.105"));
}
public InetAddress getSocketIPAddress() {
return this.serverSocket.getInetAddress();
}
public int getPort() {
return this.serverSocket.getLocalPort();
}
public void run() {
while (true) {
System.out.println("Running a thread");
try(Socket client = this.serverSocket.accept()) {
// new thread to process this client
new Thread(() -> {
try {
String data = null;
String clientAddress = client.getInetAddress().getHostName();
System.out.println("Connection from: " + clientAddress);
System.out.println("Here I am");
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
String message = "";
while (true) {
if (!((data = in.readLine()) != null && data.compareToIgnoreCase("quit") != 0)) break;
message = ("\r\nMessage from " + clientAddress + ": " + data);
System.out.println(message);
out.write(message);
}
} catch (IOException e) {
System.out.println("Something went wrong");
}
}).start();
} catch (Exception e) {
System.out.println("Something went wrong");
}
}
}
}

Ok, somehow I solved that problem, but still I need to understand how does it work:
Accepting connection inside try block, without finally block (nor try with resources) so socket is opened all the time.
Modified main method so there is no threads or runnable objects at all in it. The whole process is done within the class:
Code:
public class Main
{
public static void main(String[] args)
{
try
{
MyServerSocket socket = new MyServerSocket();
System.out.println("Port number: " + socket.getPort() + " IP address: " + socket.getSocketIPAddress());
socket.run();
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
If anyone could point me out mistakes that are still in this final version of code I'll be grateful.

Simple java chat server that only broadcasts to other clients not sender

I have been working through a tutorial for a simple java chat server and would like to modify it so that it doesn't echo back to the original sender. I have tried to mod it with my limited skills but nothing I know has worked and any help would be appreciated.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashSet;
public class ChatServer {
// Port that the server listens on.
private static final int PORT = 9001;
// Creates names
private static HashSet<String> names = new HashSet<String>();
// Creates writers
private static HashSet<PrintWriter> writers = new HashSet<PrintWriter>();
// Main method, which just listens on a port and spawns handler threads.
public static void main(String[] args) throws Exception {
System.out.println("The Chatty server is running.");
ServerSocket listener = new ServerSocket(PORT);
try {
while (true) {
new Handler(listener.accept()).start();
}
} finally {
listener.close();
}
}
private static class Handler extends Thread {
private String name;
private Socket socket;
private BufferedReader in;
private PrintWriter out;
public Handler(Socket socket) {
this.socket = socket;
}
public void run() {
try {
// Create character streams for the socket.
in = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(), true);
// Request a name from this client. Keep requesting until
// a name is submitted that is not already used. Note that
// checking for the existence of a name and adding the name
// must be done while locking the set of names.
while (true) {
out.println("SUBMITNAME");
name = in.readLine();
if (name == null) {
return;
}
synchronized (names) {
if (!names.contains(name)) {
names.add(name);
break;
}
}
}
// Now that a successful name has been chosen, add the
// socket's print writer to the set of all writers so
// this client can receive broadcast messages.
out.println("NAMEACCEPTED");
writers.add(out);
// Accept messages from this client and broadcast them.
// Ignore other clients that cannot be broadcasted to.
while (true) {
String input = in.readLine();
if (input == null) {
return;
}
// Where to add the section that prevents sending to original sender?
for (PrintWriter writer : writers) {
writer.println("MESSAGE " + name + ": " + input);
System.out.println(writer);
System.out.println("MESSAGE " + name + ": " + input);
}
}
} catch (IOException e) {
System.out.println(e);
} finally {
// This client is going down! Remove its name and its print
// writer from the sets, and close its socket.
if (name != null) {
names.remove(name);
}
if (out != null) {
writers.remove(out);
}
try {
socket.close();
} catch (IOException e) {
}
}
}
}
}
Here is the client
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
public class ChatClient {
BufferedReader in;
PrintWriter out;
JFrame frame = new JFrame("Chatty");
JTextField textField = new JTextField(40);
JTextArea messageArea = new JTextArea(8, 40);
public ChatClient() {
// Layout GUI
textField.setEditable(false);
messageArea.setEditable(false);
frame.getContentPane().add(textField, "North");
frame.getContentPane().add(new JScrollPane(messageArea), "Center");
frame.pack();
// Add Listeners
textField.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
out.println(textField.getText());
textField.setText("");
}
});
}
// Prompt for and return the desired screen name.
private String getName() {
return JOptionPane.showInputDialog(
frame,
"Choose a screen name:",
"Screen name selection",
JOptionPane.PLAIN_MESSAGE);
}
// Connects to the server then enters the processing loop.
private void run() throws IOException {
// Make connection and initialize streams
String serverAddress = "0";
Socket socket = new Socket(serverAddress, 9001);
in = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(), true);
// Process all messages from server, according to the protocol.
while (true) {
String line = in.readLine();
if (line.startsWith("SUBMITNAME")) {
out.println(getName());
} else if (line.startsWith("NAMEACCEPTED")) {
textField.setEditable(true);
} else if (line.startsWith("MESSAGE")) {
messageArea.append(line.substring(8) + "\n");
}
}
}
// Runs the client as an application with a closeable frame.
public static void main(String[] args) throws Exception {
ChatClient client = new ChatClient();
client.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
client.frame.setVisible(true);
client.run();
}
}

public class ChatServer {
// Port that the server listens on.
private static final int PORT = 9001;
// Creates names
private static HashSet<String> names = new HashSet<String>();
// Creates writers
private static HashMap<String,PrintWriter> writers = new HashMap<String,PrintWriter>();
// Main method, which just listens on a port and spawns handler threads.
public static void main(String[] args) throws Exception {
System.out.println("The Chatty server is running.");
ServerSocket listener = new ServerSocket(PORT);
try {
while (true) {
new Handler(listener.accept()).start();
}
} finally {
listener.close();
}
}
private static class Handler extends Thread {
private String name;
private Socket socket;
private BufferedReader in;
private PrintWriter out;
public Handler(Socket socket) {
this.socket = socket;
}
public void run() {
try {
// Create character streams for the socket.
in = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream(), true);
String keyForEachUser = socket.getInetAddress().toString();
// Request a name from this client. Keep requesting until
// a name is submitted that is not already used. Note that
// checking for the existence of a name and adding the name
// must be done while locking the set of names.
while (true) {
out.println("SUBMITNAME");
name = in.readLine();
if (name == null) {
return;
}
synchronized (names) {
if (!names.contains(name)) {
names.add(name);
break;
}
}
}
// Now that a successful name has been chosen, add the
// socket's print writer to the set of all writers so
// this client can receive broadcast messages.
out.println("NAMEACCEPTED");
writers.put(keyForEachUser,out);
// Accept messages from this client and broadcast them.
// Ignore other clients that cannot be broadcasted to.
while (true) {
String input = in.readLine();
if (input == null) {
return;
}
// Where to add the section that prevents sending to original sender?
for (String key : writers.keySet()) {
if (key.equalsIgnoreCase(keyForEachUser)) {
//original user founf not sending the data
}else{
PrintWriter writer = writers.get(key); //getting the correct output stream
writer.println("MESSAGE " + name + ": " + input);
System.out.println(writer);
System.out.println("MESSAGE " + name + ": " + input);
}
}
}
} catch (IOException e) {
System.out.println(e);
} finally {
// This client is going down! Remove its name and its print
// writer from the sets, and close its socket.
if (name != null) {
names.remove(name);
}
if (out != null) {
writers.remove(out);
}
try {
socket.close();
} catch (IOException e) {
}
}
}
}
}
i have made some changes to your program , problem with your earlier code was that you cant identify users connected. now im using a hashmap object to store the printwriters and the key im using in hashmap is users inetaddress which is unique from pc to pc. maybe you should try this one

Java Socketing: My server class constantly takes in input but my client doesn't?

Try to do some concurrent messaging between the server and the client. When they first connect to eachother and the Server sends the test string, the client gets it perfectly fine the first time. And the client can SEND messages just fine to the Server. But my Client class cant constantly check for messages like my Server can and idk what's wrong. Any suggestions?
Server class code:
import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.Random;
import java.util.concurrent.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class Server {
String testMessage = "You are now connected and can begin chatting!";
boolean connected = false;
int port;
public Server(int port) {
this.port = port;
}
public void Open() {
//creates Threadpool for multiple instances of chatting
final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
Runnable serverTask = new Runnable() {
#Override
public void run() {
try {
System.out.println("Opening...");
ServerSocket srvr = new ServerSocket(port);
while (true) {
Socket skt = srvr.accept();
clientProcessingPool.submit(new ClientTask(skt));
}
} catch (Exception e) {
try {
System.out.println(e);
System.out.print("You're opening too many servers in the same location, fool!\n");
ServerSocket srvr = new ServerSocket(port);
while (true) {
Socket skt = srvr.accept();
clientProcessingPool.submit(new ClientTask(skt));
}
} catch (IOException ex) {
Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
Thread serverThread = new Thread(serverTask);
serverThread.start();
}
private class ClientTask implements Runnable {
private final Socket skt;
private ClientTask(Socket skt) {
this.skt = skt;
}
#Override
public void run() {
//for sending messages
if (connected == false) {
System.out.println("======================");
System.out.println("Server has connected!");
processMessage(testMessage);
}
//for receiving messages
while (true) {
try {
// Read one line and output it
BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
String incomingMessage = br.readLine();
if (incomingMessage != null) {
System.out.println("Server: Received message: " + incomingMessage);
processMessage(incomingMessage);
}
//br.close();
//skt.close(); //maybe delete
} catch (Exception e) {
System.out.println("Server had error receiving message.");
System.out.println("Error: " + e);
}
}
}
//for processing a message once it is received
public void processMessage(String message) {
PrintWriter out = null;
try {
out = new PrintWriter(skt.getOutputStream(), true);
} catch (IOException ex) {
System.out.println(ex);
System.out.println("Server had error sending message.");
}
System.out.print("Server: Sending message: " + message + "\n");
out.print(message);
out.flush();
connected = true;
try {
skt.shutdownOutput();
//out.close();
} catch (IOException ex) {
Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
}
Client class code:
import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JOptionPane;
class Client {
public String message;
Socket skt;
public int port;
public Client(int port) {
this.port = port;
}
//for receiving messages from Server
public void receiveMessage() {
final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
Runnable serverTask = new Runnable() {
#Override
public void run() {
try {
skt = new Socket(InetAddress.getLocalHost().getHostName(), port);
while (true) {
clientProcessingPool.submit(new Client.ClientTask(skt));
}
} catch (IOException ex) {
Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
}
}
};
Thread serverThread = new Thread(serverTask);
serverThread.start();
}
//for sending messages to Server
public void sendMessage(String outgoingMessage) throws IOException {
try {
skt = new Socket(InetAddress.getLocalHost().getHostName(), port);
PrintWriter pw = new PrintWriter(skt.getOutputStream());
System.out.println("Client: Sending message: " + outgoingMessage);
pw.print(outgoingMessage);
pw.flush();
skt.shutdownOutput();
//skt.close(); //maybe delete
} catch (Exception e) {
System.out.println(e);
System.out.print("Client had error sending message.\n");
JOptionPane.showMessageDialog(null, "That User is not currently online.", "ERROR!!", JOptionPane.INFORMATION_MESSAGE);
}
}
private class ClientTask implements Runnable {
private final Socket skt;
private ClientTask(Socket skt) {
this.skt = skt;
}
#Override
public void run() {
while (true) {
try {
BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));
//while (!in.ready()) {}
String incomingMessage = in.readLine();
if (incomingMessage != null) {
System.out.println("Client: Received message: " + incomingMessage); // Read one line and output it
message = incomingMessage;
}
//skt.shutdownInput();
//in.close();
//skt.close(); //maybe delete
} catch (Exception e) {
System.out.print("Client had error receiving message.\n");
}
}
}
}
}

Streams cannot be re-wrapped. Once assigned to a wrapper, they must use that wrapper for the entire life-cycle of the stream. You also shouldn't close a stream until you are done using it, which in this case isn't until your client and server are done communicating.
In your current code, there are a few times where you re-initialize streams:
while (true) {
try {
//Each loop, this reader will attempt to re-wrap the input stream
BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
String incomingMessage = br.readLine();
if (incomingMessage != null) {
System.out.println("Server: Received message: " + incomingMessage);
processMessage(incomingMessage);
}
//don't close your stream and socket so early!
br.close();
skt.close();
} catch (Exception e) {
//...
}
You get the idea; you can use this knowledge to find the stream problems in your client code as well.
With that said, servers are the middle-man between multiple clients. If you want to be able to type in the server's console to send a message to clients, it shouldn't go to only 1 client (unless you had a system that allowed you to specify a name). You need to store every connection in some kind of collection so when you type in the server's console, it goes to every client that's connected. This also helps when a client wants to send a message to every other client (global message). The server's main thread is primarily for accepting clients; I created another thread to allow you to type in the console.
As for your streams, you should create them whenever you start the ClientTask, both server side and client side:
public class Server {
private ExecutorService executor = Executors.newFixedThreadPool(10);
private Set<User> users = new HashSet<>();
private boolean running;
private int port;
public Server(int port) {
this.port = port;
}
public void start() {
running = true;
Runnable acceptor = () -> {
try(ServerSocket ss = new ServerSocket(port)) {
while(running) {
User client = new User(ss.accept());
users.add(client);
executor.execute(client);
}
} catch(IOException e) {
//if a server is already running on this port;
//if the port is not open;
e.printStackTrace();
}
};
Runnable userInputReader = () -> {
try(Scanner scanner = new Scanner(System.in)) {
while(running) {
String input = scanner.nextLine();
for(User user : users) {
user.send(input);
}
}
} catch(IOException e) {
//problem sending data;
e.printStackTrace();
}
};
Thread acceptorThread = new Thread(acceptor);
Thread userThread = new Thread(userInputReader);
acceptorThread.start();
userThread.start();
}
public void stop() {
running = false;
}
public static void main(String[] args) {
new Server(15180).start();
System.out.println("Server started!");
}
}
In the run() method is where the streams should be wrapped.
class User implements Runnable {
private Socket socket;
private boolean connected;
private DataOutputStream out; //so we can access from the #send(String) method
public User(Socket socket) {
this.socket = socket;
}
public void run() {
connected = true;
try(DataInputStream in = new DataInputStream(socket.getInputStream())) {
out = new DataOutputStream(socket.getOutputStream());
while(connected) {
String data = in.readUTF();
System.out.println("From client: "+data);
//send to all clients
}
} catch(IOException e) {
//if there's a problem initializing streams;
//if socket closes while attempting to read from it;
e.printStackTrace();
}
}
public void send(String message) throws IOException {
if(connected) {
out.writeUTF(message);
out.flush();
}
}
}
It's pretty much the same idea with the client:
1. Connect to Server
2. Create "communication" thread
3. Create "user input" thread (to receive input from console)
4. Start threads
public class Client {
private final String host;
private final int port;
private boolean connected;
private Socket socket;
public Client(String host, int port) {
this.host = host;
this.port = port;
}
public void start() throws IOException {
connected = true;
socket = new Socket(host, port);
Runnable serverInputReader = () -> {
try (DataInputStream in = new DataInputStream(socket.getInputStream())) {
while (connected) {
String data = in.readUTF();
System.out.println(data);
}
} catch (IOException e) {
// problem connecting to server; problem wrapping stream; problem receiving data from server;
e.printStackTrace();
}
};
Runnable userInputReader = () -> {
try (DataOutputStream out = new DataOutputStream(socket.getOutputStream());
Scanner scanner = new Scanner(System.in)) {
while (connected) {
String input = scanner.nextLine();
out.writeUTF(input);
}
} catch (IOException e) {
//problem wrapping stream; problem sending data;
e.printStackTrace();
}
};
Thread communicateThread = new Thread(serverInputReader);
Thread userThread = new Thread(userInputReader);
communicateThread.start();
userThread.start();
}
public static void main(String[] args) throws IOException {
new Client("localhost", 15180).start();
}
}
There are a few things I used in the code above that you may not be familiar with. They help simplify the syntax for your code:
Lambda Expressions - Prevents the need to create an anonymous class (or subclass) to declare a method
Try-With-Resources - Closes the resources specified automatically once the try block as ended
EDIT
When a user connects, you should store their connection by name or id. That way, you can send data to specific users. Even if your client is running on the same machine as the server, it's still the same idea: client connects to server, server sends message to client based on name or id:
while(running) {
User client = new User(ss.accept());
users.add(client); //add to set
executor.execute(client);
}
Right now, you are simply adding users to a Set. There is currently no way to grab a specific value from this set. What you need to do is give it some kind of "key". To give you an idea, here's an old algorithm I used to use. I have an array full of empty slots. When someone connects, I look for the first empty slot. Once an empty slot is found, I pass the user the index of the array it's being stored at (that will be the user's id), then store the user in the array at the specified index. When you need to send a message to someone, you can use the id to access that specific array index, grab the user you want and send a message:
class Server {
private int maxConnections = 10;
private ExecutorService executor = Executors.newFixedThreadPool(maxConnections);
private User[] users = new User[maxConnections];
//...
while(running) {
Socket socket = ss.accept();
for(int i = 0; i < users.length; i++) {
if(users[i] == null) {
users[i] = new User(socket, i);
executor.execute(users[i]);
break;
}
}
}
//...
public static void sendGlobalMessage(String message) throws IOException {
for(User user : users)
if(user != null)
user.send(message);
}
public static void sendPrivateMessage(String message, int id) {
User user = users[id];
if(user != null) {
user.send(message);
}
}
}
class User {
private Socket socket;
private int id;
private DataOutputStream out;
public User(Socket socket, int id) {
this.socket = socket;
this.id = id;
}
public void send(String message) throws IOException {
out.writeUTF(message);
out.flush();
}
public void run() {
DataInputStream in;
//wrap in and out streams
while(connected) {
String data = in.readUTF();
//Server.sendGlobalMessage(data);
//Server.sendPrivateMessage(data, ...);
sendMessage(data); //sends message back to client
}
}
}