Develop Reference

Sending a Message to Multiple Clients from One Server Simultaneously?

I am currently working on a TCP Sockets program in Java in which two or more separate clients connect to a single server, and that server will send a message to both of these connected clients simultaneously.
I've tried to work through the code multiple times, but I can't quite seem to be able to have one message be sent to both clients.
Below is a reduced version of my entire code, condensed down to just the issue I'm having.
I've also included a video, just to save you the effort of having to copy and run my code!
[STREAMABLE LINK]
When one client is connected, I just have to write one message in the server, press send, and it shows up in the client.
When two clients are connected, I have to write two messages in the server and press send twice, and one message goes to one client and the other to the next client.
How can I make it so I only send one message from the server that goes to all clients?
I greatly appreciate any and all help.
SERVER CODE:
import java.io.*;
import java.net.*;
import java.util.*;
// Server class
class Server {
public class countLogic {
public static int client_count = 0;
}
public static void main(String[] args) {
System.out.println("[SERVER]");
ServerSocket server = null;
try {
server = new ServerSocket(1234);
server.setReuseAddress(true);
while (true) {
Socket client = server.accept();
countLogic.client_count++;
System.out.println("Client ("+countLogic.client_count+") connected: " + client.getInetAddress().getHostAddress());
ClientHandler clientSock = new ClientHandler(client);
new Thread(clientSock).start();
}
}
catch (IOException e) {
e.printStackTrace();
}
finally {
if (server != null) {
try {
server.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
}
}
// ClientHandler class
private static class ClientHandler implements Runnable {
private final Socket clientSocket;
public ClientHandler(Socket socket)
{
this.clientSocket = socket;
}
public void run()
{
PrintWriter out = null;
BufferedReader in = null;
try {
Scanner sc = new Scanner(System.in);
out = new PrintWriter(clientSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String line = null;
while (true) {
line = sc.nextLine();
out.println(line);
}
}
catch (IOException e) {
e.printStackTrace();
}
finally {
try {
if (out != null) {
out.close();
}
if (in != null) {
in.close();
clientSocket.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
CLIENT CODE:
import java.io.*;
import java.net.*;
import java.util.*;
// Client class
class Client {
// driver code
public static void main(String[] args)
{
System.out.println("[CLIENT 1]");
try (Socket socket = new Socket("localhost", 1234)) {
PrintWriter out = new PrintWriter(
socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
Scanner sc = new Scanner(System.in);
String line = null;
while (!"exit".equalsIgnoreCase(line)) {
System.out.println("Server: "+ in.readLine());
}
// closing the scanner object
sc.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
}

Handler thread hanging on reading in

I am trying to set up a server with a client and a handler. The client should ask for a string from the user. This should then be written to an OutputStream, get read in by the handler which then saves the string to its own OutputStream before passing it back to the client. I know that this program is completely pointless, I am just trying to get my head around how servers, clients and handlers work.
Here is my code so far:
Server
public class Server {
public static void main (String args[]) throws IOException {
int port = 8080;
ServerSocket server = new ServerSocket(port);
while (true) {
System.out.println("Waiting for client...");
Socket client = server.accept();
System.out.println("Client from "+client.getInetAddress()+" connected.");
Handler handler = new Handler(client);
handler.run();
}
}
}
Handler
class Handler extends Thread {
private Socket client;
public Handler(Socket c) {
client = c;
}
public void run() {
try {
Thread.sleep(3000);
System.out.println("1");
PrintWriter out = new PrintWriter(new OutputStreamWriter(client.getOutputStream()));
BufferedReader in =
new BufferedReader(new InputStreamReader(client.getInputStream(),
"UTF-8"));
System.out.println("2");
String message = in.readLine();
System.out.println("4");
System.out.println("5");
out.println(message);
out.flush();
client.close();
System.out.println("Finish");
} catch (IOException e1) {
e1.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
Client
public class Client {
public static void main (String args[]) throws IOException {
Socket server = new Socket("127.0.0.1", 8080);
System.out.println("Attempting connection...");
Scanner scan = new Scanner (System.in);
System.out.println("Please enter a string:");
String message = scan.next();
PrintWriter out = new PrintWriter(new OutputStreamWriter(server.getOutputStream()));
BufferedReader in =
new BufferedReader(new InputStreamReader(server.getInputStream(),
"UTF-8"));
out.println(message);
String messageReturn = in.read();
scan.close();
System.out.println("Server said: " + messageReturn);
in.close();
out.close();
}
}
The problem is that the handler seems to hang when it tries to read the message in. This problem seems similar to the one presented here: Socket problem - readline won't work properly
But this solution isn't working for me. I have tried using objectInputStreams instead of my current solution, but this didn't work either.

I doubt whether your client code will compile. The return type for this is int.
String messageReturn = in.read();
Anyway, this should work:
package network;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
public class Client {
public static void main (String args[]) throws IOException {
Socket server = new Socket("127.0.0.1", 9890);
System.out.println("Attempting connection...");
Scanner scan = new Scanner (System.in);
System.out.println("Please enter a string:");
String message = scan.next();
PrintWriter out = new PrintWriter(new OutputStreamWriter(server.getOutputStream()));
BufferedReader in = new BufferedReader(new InputStreamReader(server.getInputStream(), "UTF-8"));
out.println(message);
// NOTE this
String messageReturn = in.readLine();
scan.close();
System.out.println("Server said: " + messageReturn);
in.close();
out.close();
}
}
Note Port has been changed.
Server Output
Waiting for client...
Client from /127.0.0.1 connected.
1
Client Output
Attempting connection...
Please enter a string:
Hello

The problem might be that you do not send an escape sequence with your response. ReadLine() waits till it gets an escape. Try sending a "\n" with your response. There is an article about problems using readLine() and println() with sockets. It also shows how to solve it.
ReadLine() / Println() and sockets

Unable to get message from client in client-server program in java

I am writing a client-server program in java using TCP/IP. For the purpose, I wrote the following codes:
serversock.java:
import java.net.*;
import java.io.*;
public class serversock {
public static void main(String[] args) throws IOException
{
ServerSocket sersock = null;
try
{
sersock = new ServerSocket(10007);
}
catch (IOException e)
{
System.out.println("Can't listen to port 10007");
System.exit(1);
}
Socket clientSocket = null;
System.out.println("Waiting for connection....");
try
{
clientSocket = sersock.accept();
}
catch ( IOException ie)
{
System.out.println("Accept failed..");
System.exit(1);
}
System.out.println("Conncetion is established successfully..");
System.out.println("Waiting for input from client...");
PrintWriter output = new PrintWriter(clientSocket.getOutputStream());
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String inputLine = input.readLine();
while ( inputLine != null)
{
output.println(inputLine);
System.out.println("Server: " + inputLine);
inputLine = input.readLine();
}
input.close();
clientSocket.close();
sersock.close();
}
}
clientsock.java:
import java.util.*;
import java.io.*;
import java.net.*;
public class clientsock
{
public static void main(String[] args) throws IOException
{
Socket sock = new Socket("localhost",10007);
// Scanner scan = new Scanner(System.in);
PrintWriter output = new PrintWriter(sock.getOutputStream(),true);
BufferedReader input = new BufferedReader( new InputStreamReader(sock.getInputStream()));
String line = null;
BufferedReader stdInput = new BufferedReader( new InputStreamReader(System.in));
System.out.println("Enter data to send to server: ");
line = stdInput.readLine();
while ( (line) != "bye")
{
output.println(line.getBytes());
line = stdInput.readLine();
System.out.println("Server sends: " + input.read());
}
sock.close();
}
}
Now on running the programs I got the following output:
server:
shahjahan#shahjahan-AOD270:~/Documents/java$ java serversock
Waiting for connection....
Conncetion is established successfully..
Waiting for input from client...
Server: [B#4e25154f
shahjahan#shahjahan-AOD270:~/Documents/java$
client:
shahjahan#shahjahan-AOD270:~/Documents/java$ java clientsock
Enter data to send to server:
qwe
sdf
^Cshahjahan#shahjahan-AOD270:~/Documents/java$
The server is recieving different symbols, and client receives nothing. Please help me to solve it.

In the client replace:
output.println(line.getBytes());
with
output.println(line);

Multiple client server in which a client can only send message to server but server to all clients in java

I want that message sent by server should be delivered to all the clients however a message sent by by client should only be delivered to server.
Problem is when i run the code-
1.Server waits for client to connect
2.when multiple client connected
3.Now as the server broadcast the first message it is received by both the clients but when server broadcast the message second time. Both the clients has to send message in order to receive server message.
I am a noob in socket programming so please correct me what i am doing wrong?
So far i have made this program.
Server Code:
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Scanner;
import java.net.*;
import java.io.*;
public class Server_Side3
{
static Client_server t[] = new Client_server[10];
static LinkedList<Client_server> al = new LinkedList<Client_server>();
public static void main(String args[]) throws IOException
{
ServerSocket server = null ;
Socket socket = null;
try
{
int Port =9777;
server = new ServerSocket(Port);
System.out.println("Waiting for Client " + server);
while(true)
{
socket = server.accept();
System.out.println("Connected to " + socket.getLocalAddress().getHostAddress());
Client_server clients = new Client_server(socket);
al.add(clients);
clients.start();
}
}
catch (Exception e)
{
System.out.println("An error occured.");
e.printStackTrace();
}
try
{
server.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
private static class Client_server extends Thread
{
Socket sockets;
PrintWriter out;
Client_server t[];
Client_server (Socket s )
{
sockets = s;
}
public void run()
{
try
{
InetAddress localaddr = InetAddress.getLocalHost();
Scanner sc = new Scanner(System.in);
Scanner in = new Scanner(sockets.getInputStream());
out = new PrintWriter(sockets.getOutputStream(),true);
String input = null;
while(true)
{
String servermsg = sc.nextLine();
broadcast(servermsg);
System.out.println("Message sent to client: "+servermsg);
input = in.nextLine();
System.out.println(localaddr.getHostName()+" Said :"+ input);
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
private void broadcast(String servermsg)
{
Iterator it = al.iterator();
while(it.hasNext())
{
((Client_server) it.next()).send(servermsg);
}
}
private void send(String msg)
{
String servrmsg = msg;
out.println(msg);
out.flush();
}
}
}
Client Code :
import java.net.Socket;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
public class ClientSide2
{
static Scanner chat = new Scanner(System.in);
public static void main(String[] args)
{
int Port = 9777;
String Host = "localhost";
try
{
Socket socket = new Socket(Host, Port);
System.out.println("You connected to "+ Host);
Scanner in = new Scanner(socket.getInputStream()); //GET THE CLIENTS INPUT STREAM
PrintWriter out = new PrintWriter(socket.getOutputStream());
String clientinput;
while(true)
{
System.out.println(in.nextLine());//If server has sent us something .Print it
clientinput=chat.nextLine();
out.println(clientinput); //SEND IT TO THE SERVER
out.flush();
}
}
catch (Exception e)
{
System.out.println("The server might not be up at this time.");
System.out.println("Please try again later.");
}
}
}

java.io.StreamCorruptedException: invalid stream header: 72657175

Hey I am implementing an electronic voting system based on client server chat.
When I run the server it runs without any problems but without printing as well and also the client. But as soon as I give the input to the client, it gives me the following exception and crashes. Here is the code of the server and the client. So what do u think I should do to start the engine?
package engine;
import java.io.*;
import java.net.*;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collections;
import java.util.GregorianCalendar;
public class Server {
ServerSocket server;
int port = 6000;
public Server() {
try {
server = new ServerSocket(6000);
} catch (IOException e) {
e.printStackTrace();
}
}
public void handleConnection(){
try {
while(true){
Socket connectionSocket;
connectionSocket = server.accept();
new ConnectionHandler(connectionSocket);
}
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
Server server = new Server();
server.handleConnection();
}
}
class ConnectionHandler implements Runnable {
Socket connectionSocket;
Calendar votingStartTime;
Calendar votingEndTime;
boolean timeUp;
ObjectInputStream inFromClient;
ObjectOutputStream outToClient;
BufferedWriter outToFile;
BufferedReader inFromAdmin;
ArrayList<SingleClient> clients = new ArrayList<SingleClient>();
ArrayList<Candidate> candidates;
this is the part of the code the Exception comes from:
public ConnectionHandler(Socket socket) {
try {
this.connectionSocket = socket;
votingStartTime = new GregorianCalendar();
outToClient = new ObjectOutputStream(
connectionSocket.getOutputStream());
inFromClient = new ObjectInputStream(
connectionSocket.getInputStream());
inFromAdmin = new BufferedReader(new InputStreamReader(System.in));
startVotingSession();
Thread t = new Thread(this);
t.start();
} catch (IOException e) {
e.printStackTrace();
}
}
and this is the client's main method the Exception as soon as i give the input:
public static void main(String[] args) throws Exception {
client c = new client();
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String input;
while(true){
input = br.readLine();
if(input.equals("0")){
c.register();
}else if(input.equals("1")){
c.login();
}else if(input.equals("2")){
c.listCandidates();
}else if(input.equals("3")){
c.vote();
}else if(input.equals("4")){
c.checkResults();
}else if(input.equals("5")){
c.checkFinalResults();
}else if(input.equals("6")){
c.logout();
}else {
break;
}
}
}
}

without seeing the relevant code, i would guess you are recreating the ObjectInputStream on an existing socket InputStream. you must create the object streams once per socket and re-use them until you are completely finished with the socket connection. also, you should always flush the ObjectOutputStream immediately after creation to avoid deadlock.