my server class
import java.net.*;
import java.io.*;
public class server
{
private Socket socket;
private ServerSocket server;
// constructor with port
public void start(int port){
try {
server = new ServerSocket(port);
while(true){
socket = server.accept();
new ConnectionHandler(socket).run();
}
}catch(IOException i){
}
}
}
class ConnectionHandler implements Runnable{
private Socket socket = null;
private ServerSocket server = null;
private DataInputStream in = null;
public ConnectionHandler(Socket socket){
this.socket=socket;
}
#Override
public void run() {
InputStream inp = null;
BufferedReader brinp = null;
DataOutputStream out = null;
try
{
System.out.println("Waiting for a client ...");
System.out.println(server);
System.out.println("Client accepted");
in = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
String line = "";
// reads message from client until "Over" is sent
while (!line.equals("Over"))
{
try
{
line = in.readUTF();
System.out.println(line);
}
catch(IOException i)
{
System.out.println(i);
}
}
System.out.println("Closing connection");
// close connection
socket.close();
in.close();
}
catch(IOException i)
{
System.out.println(i);
}
}
public static void main(String[] args) {
server serverr = new server();
serverr.start(4000);
}
}
Here's my client class.
import java.net.*;
import java.io.*;
public class Client
{
// initialize socket and input output streams
private Socket socket = null;
private DataInputStream input = null;
private DataOutputStream out = null;
// constructor to put ip address and port
public Client(String address, int port)
{
// establish a connection
try
{
socket = new Socket(address, port);
System.out.println("Connected");
// takes input from terminal
input = new DataInputStream(System.in);
// sends output to the socket
out = new DataOutputStream(socket.getOutputStream());
}
catch(UnknownHostException u)
{
System.out.println(u);
}
catch(IOException i)
{
System.out.println(i);
}
// string to read message from input
String line = "";
// keep reading until "Over" is input
while (!line.equals("Over"))
{
try
{
line = input.readLine();
out.writeUTF(line);
}
catch(IOException i)
{
System.out.println(i);
}
}
// close the connection
try
{
input.close();
out.close();
socket.close();
}
catch(IOException i)
{
System.out.println(i);
}
}
public static void main(String args[])
{
Client client = new Client("127.0.0.1", 4000);
}
}
Trying to develop pretty simple chat application works via terminal, but I think there are plenty of bugs I have in my code.
The server can handle one client, but when another client comes up it doesn't connect to other clients.
What am I have to do now?
I couldn't find out where my problem is, waiting your helps.
Note: I am completely new to socket programming concept.
The ConnectionHandler class is a thread class, and you must wrap its object to a Thread instance and then call start() instead of run().
So in the Server class change
new ConnectionHandler(socket).run();
with
new Thread(ConnectionHandler(socket)).start();
Related
The program is intended to have multiple clients connect to a single server and the clients are able to send and receive messages among other clients.
For example if Client A says "Hi", Client B and Client C connected to the server would also receive "Hi".
In my current code, the server only receives the messages sent by the clients.
I'm currently looking for a solution to have the server broadcast the message sent by a client (eg. ClientA) to other clients. Any advice would be much appreciated.
This server class handles the connections of multiple clients with the use of threads:
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
class EchoThread extends Thread {
private Socket socket;
//constructor
public EchoThread(Socket clientSocket) {
this.socket = clientSocket;
}
#Override
public void run() {
DataInputStream inp = null;
try {
inp = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
//print whatever client is saying as long as it is not "Over"
String line = "";
while (!line.equals("Over")) {
try {
line = inp.readUTF();
System.out.println(line);
} catch (IOException e) { System.out.println(e); }
}
//closes connection when client terminates the connection
System.out.print("Closing Connection");
socket.close();
} catch (IOException e) { System.out.println(e); }
}
}
public class Server {
private static final int PORT = 5000;
public static void main(String args[]) {
ServerSocket serverSocket = null;
Socket socket = null;
//starts the server
try {
serverSocket = new ServerSocket(PORT);
System.out.println("Server started");
System.out.println("Waiting for a client ...\n");
} catch (IOException e) { System.out.println(e); }
//while loop to accept multiple clients
int count = 1;
while(true) {
try {
socket = serverSocket.accept();
System.out.println("Client " + count + " accepted!");
count++;
} catch (IOException e) { System.out.println(e); }
//starts the server thread
new EchoThread(socket).start();
}
}
}
and this is the client class (I have multiple instances of this code running):
import java.net.*;
import java.io.*;
public class ClientA {
private Socket socket = null;
private DataInputStream input = null;
private DataOutputStream output = null;
public ClientA(String address, int port) {
//establish connection
try {
socket = new Socket(address, port);
System.out.println("Connected");
//takes input from terminal
input = new DataInputStream(System.in);
//sends output to the socket
output = new DataOutputStream(socket.getOutputStream());
} catch (IOException e) { System.out.println(e); }
//string to read message from input
String line = "";
//keep reading until "Over" is input
while (!line.equals("Over")) {
try {
line = input.readLine();
output.writeUTF(line);
} catch (IOException e) { System.out.println(e); }
}
//close the connection
try {
input.close();
output.close();
socket.close();
} catch (IOException e) { System.out.println(e); }
}
public static void main (String args[]) {
ClientA client = new ClientA("127.0.0.1", 5000);
}
}
Do feel free to correct me on my code comments as I'm still not very familiar with socket programming.
You did well. Just add a thread to receive message in ClientA; and store socket clients in Server.
In fact, Server is also a "client" when is send message to client.
I add some code based on your code. It works well, hope it's helpful.
class EchoThread extends Thread {
//*****What I add begin.
private static List<Socket> socketList = new ArrayList<>();
//*****What I add end.
private Socket socket;
//constructor
public EchoThread(Socket clientSocket) {
this.socket = clientSocket;
socketList.add(socket);
}
#Override
public void run() {
DataInputStream inp = null;
try {
inp = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
//print whatever client is saying as long as it is not "Over"
String line = "";
while (!line.equals("Over")) {
try {
line = inp.readUTF();
System.out.println(line);
//*****What I add begin.
sendMessageToClients(line);
//*****What I add end.
} catch (IOException e) { System.out.println(e); break;}
}
//closes connection when client terminates the connection
System.out.print("Closing Connection");
socket.close();
} catch (IOException e) { System.out.println(e); }
}
//*****What I add begin.
private void sendMessageToClients(String line) throws IOException {
for (Socket other : socketList) {
if (other == socket) {
continue;//ignore the sender client.
}
DataOutputStream output = new DataOutputStream(other.getOutputStream());
output.writeUTF(line);
}
}
//*****What I add end.
}
public class ClientA {
private Socket socket = null;
private DataInputStream input = null;
private DataOutputStream output = null;
public ClientA(String address, int port) {
//establish connection
try {
socket = new Socket(address, port);
System.out.println("Connected");
//takes input from terminal
input = new DataInputStream(System.in);
//sends output to the socket
output = new DataOutputStream(socket.getOutputStream());
//*****What I add begin.
//Here create a thread to receive message from server.
DataInputStream inp = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
new Thread(() -> {
while (true) {
String str;
try {
str = inp.readUTF();
System.out.println(str);
} catch (IOException e) {
e.printStackTrace();//error.
break;
}
}
}, "Client Reveiver.").start();
//*****What I add end.
} catch (IOException e) { System.out.println(e); }
//string to read message from input
String line = "";
//keep reading until "Over" is input
while (!line.equals("Over")) {
try {
line = input.readLine();
output.writeUTF(line);
} catch (IOException e) { System.out.println(e); }
}
//close the connection
try {
input.close();
output.close();
socket.close();
} catch (IOException e) { System.out.println(e); }
}
I would have a single server thread which would maintain a register of the clients, possibly in a concurrent collection. Then I would send each message received from a client to all other clients.
I recently wrote a socket communication program in java where two threads run concurrent on each server and client side handling the read and write operations to the socket allowing continuous message sending and receiving on both sides.
The problem is either of the client or the server stops receiving communication from the other side and then after a while both of them stop working. I can't figure out what's wrong and how the connection is dropping :/
Code for server
import java.net.*;
import java.io.*;
import java.util.Scanner;
public class Server
{
private Socket socket = null;
private ServerSocket server = null;
private DataInputStream in = null;
private DataOutputStream out = null;
private Scanner inp = null;
String line = "";
String iline = "";
public Server(int port)
{
try
{
server = new ServerSocket(port);
System.out.println("Server started");
System.out.println("Waiting for a client ...");
socket = server.accept();
System.out.println("Client accepted");
// takes input from the client socket
out=new DataOutputStream(socket.getOutputStream());
in = new DataInputStream(new
BufferedInputStream(socket.getInputStream()));
inp = new Scanner(System.in);
while (true)
{
new Thread(new Runnable(){
public void run()
{
try{
while(true){
line = in.readUTF();
System.out.println("Client : "+line);
if(socket.isClosed()||socket.isOutputShutdown()||socket.isInputShutdown())
{
System.out.println("DED");
System.exit(0);
}
}
}
catch(Exception e){
System.out.println("Exception !!!");
}
}
}).start();
iline=inp.nextLine();
out.writeUTF(iline);
if(socket.isClosed()||socket.isOutputShutdown()||socket.isInputShutdown()){
System.out.println("DED");
System.exit(0);
}
}
}
catch(IOException i)
{
System.out.println(i);
}
}
public static void main(String args[])
{
Server server = new Server(5000);
}
}
Code for Client
import java.net.*;
import java.io.*;
import java.util.Scanner;
class Client{
private Socket socket =null;
private DataInputStream inp=null;
private DataOutputStream out=null;
private Scanner in=null;
String line="";
String iline="";
Client(String address,int port)
{
try{
socket = new Socket(address,port);
in= new Scanner(System.in);
out = new DataOutputStream(socket.getOutputStream());
inp = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
while(true){
line=in.nextLine();
out.writeUTF(line);
new Thread(new Runnable(){
public void run()
{
try{
while(true){
iline=inp.readUTF();
System.out.println("Server : "+iline);
if(socket.isClosed()||socket.isOutputShutdown()||socket.isInputShutdown()){
System.out.println("DED");
System.exit(0);
}
}
}
catch(Exception e){
System.out.println("Exception !!!");
}
}
}).start();
if(socket.isClosed()||socket.isOutputShutdown()||socket.isInputShutdown()){
System.out.println("DED");
System.exit(0);
}
}
}
catch(UnknownHostException u)
{
System.out.println(u);
}
catch(Exception e){
System.out.println("EXCEPTION!!!");
}
}
}
class ClientSocket{
public static void main(String...args){
Client obj = new Client("127.0.0.1", 5000);
}
}
Just an initial run through your code what I see is in the first while(true){} , you are spawning a thread calling start method on it . The moment you start the reading thread the main thread checks fo sockets conditions and moves ahead. Since there is a true in your first while(true) a new thread is again spawned and that goes on an on until the socket is closed where the programs terminates because of system.exit call.
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 4 years ago.
I wrote a java application for both Server and Client. What I want to do is stop the Client's application(and all of it's threads) when the user enters the word: "logout". I've tried everything I could find so kinda desperate here. Please send help!
Here is my code for Client.java
package client;
//Java implementation for multithreaded chat client
//Save file as Client.java
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class Client extends Thread
{
final static int ServerPort = 1234;
private volatile static boolean running = true;
public static void main(String args[]) throws UnknownHostException, IOException
{
Scanner scn = new Scanner(System.in);
// getting localhost ip
InetAddress ip = InetAddress.getByName("localhost");
// establish the connection
Socket s = new Socket(ip, ServerPort);
// obtaining input and out streams
DataInputStream dis = new DataInputStream(s.getInputStream());
DataOutputStream dos = new DataOutputStream(s.getOutputStream());
// sendMessage thread
Thread sendMessage = new Thread(new Runnable()
{
#Override
public void run() {
while (running) {
// read the message to deliver.
try {
String msg = scn.nextLine();
if(msg == "logout") {
running = false;
dis.close();
dos.close();
scn.close();
s.close();
Thread.currentThread().interrupt();
break;
}
dos.writeUTF(msg);
}
catch (IOException e) {
if(!running) {
System.out.println("Closing...");
System.exit(0);
}
}
} }
});
// readMessage thread
Thread readMessage = new Thread(new Runnable()
{
#Override
public void run() {
while (running) {
// read the message sent to this client
try {
String msg = dis.readUTF();
if(sendMessage.isInterrupted()) {
running = false;
dis.close();
dos.close();
scn.close();
s.close();
Thread.currentThread().interrupt();
break;
}
System.out.println(msg);
} catch (IOException e) {
if(!running) {
System.out.println("Closing...");
System.exit(0);
}
}
}
}
});
sendMessage.start();
readMessage.start();
}
}
And this is my Server.java
package server;
//Java implementation of Server side
//It contains two classes : Server and ClientHandler
//Save file as Server.java
import java.io.*;
import java.util.*;
import java.net.*;
//Server class
public class Server
{
// Vector to store active clients
static Vector<ClientHandler> ar = new Vector<>();
// counter for clients
static int i = 0;
public static void main(String[] args) throws IOException
{
// server is listening on port 1234
ServerSocket ss = new ServerSocket(1234);
Socket s;
// running infinite loop for getting
// client request
while (true)
{
// Accept the incoming request
s = ss.accept();
System.out.println("New client request received : " + s);
// obtain input and output streams
DataInputStream dis = new DataInputStream(s.getInputStream());
DataOutputStream dos = new DataOutputStream(s.getOutputStream());
System.out.println("Creating a new handler for this client...");
// Create a new handler object for handling this request.
ClientHandler mtch = new ClientHandler(s,"client " + i, dis, dos);
// Create a new Thread with this object.
Thread t = new Thread(mtch);
System.out.println("Adding this client to active client list");
// add this client to active clients list
ar.add(mtch);
// start the thread.
t.start();
// increment i for new client.
// i is used for naming only, and can be replaced
// by any naming scheme
i++;
}
}
}
//ClientHandler class
class ClientHandler implements Runnable
{
private String name;
final DataInputStream dis;
final DataOutputStream dos;
Socket s;
boolean isloggedin;
// constructor
public ClientHandler(Socket s, String name,
DataInputStream dis, DataOutputStream dos) {
this.dis = dis;
this.dos = dos;
this.name = name;
this.s = s;
this.isloggedin=true;
}
#Override
public void run() {
String received;
while (true)
{
try
{
// receive the string
received = dis.readUTF();
if(received.equals("logout")){
break;
}
// break the string into message and recipient part
StringTokenizer st = new StringTokenizer(received, "#");
String MsgToSend = st.nextToken();
String recipient = st.nextToken();
// search for the recipient in the connected devices list.
// ar is the vector storing client of active users
for (ClientHandler mc : Server.ar)
{
// if the recipient is found, write on its
// output stream
if (mc.name.equals(recipient) && mc.isloggedin==true)
{
mc.dos.writeUTF(this.name+" : "+MsgToSend);
break;
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
try
{
// closing resources
this.dis.close();
this.dos.close();
this.s.close();
this.isloggedin=false;
}catch(IOException e){
e.printStackTrace();
}
}
}
Code reference: Multithread GroupChat 1
Multithread GroupChat 2
Don't compare Strings with == but with equals(). msg == "logout" Should be msg.equals("logout").
I'm trying to code an instant messaging system... Initially, I'm doing it this way, and once I get it to work I'll add the GUI.
Once a client sends a message to the server, the server is supposed to display it to all the other clients. How can I do that? I've been trying a few things but it keeps displaying only to the client that sent the message...
Thanks in advance!
SERVER
import java.io.*;
import java.net.*;
class Server {
//one per server
static int port = 3000;
private int backlog = 100;
ServerSocket main;
static DataOutputStream dataOut;
static DataInputStream dataIn;
static String scannerMessage;
static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
static class MailServer extends Thread {
//one per client
static int index;
String name = Client.name;
public MailServer(int index, DataInputStream in, DataOutputStream out) {
Server.dataIn = in;
Server.dataOut = out;
this.index = index; // thread index, one per client
}
public void run() {
while (true) {
try {
String receivedMessage = dataIn.readUTF();
//print receivedMessage to all clients
} catch (Exception e) {
break;
}
}
}
}
public Server(int port) throws Exception {
this.main = new ServerSocket(port);
}
// start a serve
public void serve() throws Exception {
int index = 1;
while (true) {
Socket socket = this.main.accept();
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
DataInputStream dataIn = new DataInputStream(in);
DataOutputStream dataOut = new DataOutputStream(out);
// handle the connection
// keep reading using an infintite loop
System.out.println("Handling connection to Client " + index + "...");
(new MailServer(index, dataIn, dataOut)).start();
index += 1; // add one every time a new client is added
}
}
public static void main(String[] args) throws Exception {
Server s = new Server(port);
System.out.println("Serving....");
s.serve();
}
}
CLIENT
import java.io.*;
import java.net.*;
class Client {
static String hostname = "127.0.0.1";
static int port = Server.port;
static Socket socket;
static String name;
static class Sender extends Thread {
DataOutputStream dataOut;
public Sender(DataOutputStream dataOut) {
this.dataOut = dataOut;
}
public void run() {
while(true) {
//get a message from the user
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
try {
String message = br.readLine();
dataOut.writeUTF(message);
dataOut.flush();
} catch(Exception e) {
break;
}
}
}
}
static class Receiver extends Thread {
DataInputStream dataIn;
public Receiver(DataInputStream dataIn) {
this.dataIn = dataIn;
}
public void run() {
while(true) {
try {
//RECEIVE A MESAGE FROM THE SERVER (ending in \n)
String msg = dataIn.readUTF();
while (msg != null) {
System.out.println(msg);
msg = dataIn.readUTF();
}
} catch(Exception e) {
break;
}
}
}
}
//client will require host name and the port
public Client(String hostname, int port) throws Exception {
socket = new Socket(hostname, port);
}
public void connect() throws Exception {
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
DataInputStream dataIn = new DataInputStream(in);
DataOutputStream dataOut = new DataOutputStream(out);
//handle the connection
System.out.println("Handling connection to server...");
Thread sender = new Sender(dataOut);
Thread receiver = new Receiver(dataIn);
sender.start();
receiver.start();
sender.join();
receiver.join();
System.out.println("Client " + Server.MailServer.index);
System.out.println("----------------------");
}
public static void main(String[] args) throws Exception {
Client c = new Client(hostname, port);
c.connect();
}
}
Update: I created a list of all the MailServer objects and then iterated through them to send the message to all the clients, as JP Moresmau suggested... but now the first Client to send something receives all the outputs. Why is this? How can I fix it... ? Thank you, and sorry if my questions seem too obvious or dumb, I'm still a Java noob:(
SERVER - UPDATED
package csci2020_assignment51;
import java.io.*;
import java.net.*;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
class Server {
//one per server
static int port = 3000;
private int backlog = 100;
ServerSocket main;
static DataOutputStream dataOut;
static DataInputStream dataIn;
static String scannerMessage;
static List<MailServer> mailServers = Collections.<MailServer>synchronizedList(new ArrayList<MailServer>());
static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
static class MailServer extends Thread {
//one per client
static int index;
String name = Client.name;
public MailServer(int index, DataInputStream in, DataOutputStream out) {
Server.dataIn = in;
Server.dataOut = out;
this.index = index; // thread index, one per client
}
public void run() {
while (true) {
try {
String receivedMessage = dataIn.readUTF();
String outputMessage = "Client " + index + " said: " + receivedMessage;
//print receivedMessage to all clients
for (MailServer mailserver : mailServers) {
dataOut.writeUTF(outputMessage);
}
} catch (Exception e) {
break;
}
}
}
}
public Server(int port) throws Exception {
this.main = new ServerSocket(port);
}
// start a serve
public void serve() throws Exception {
int index = 1;
while (true) {
Socket socket = this.main.accept();
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
DataInputStream dataIn = new DataInputStream(in);
DataOutputStream dataOut = new DataOutputStream(out);
// handle the connection
// keep reading using an infintite loop
System.out.println("Handling connection to Client " + index + "...");
MailServer mailServer = new MailServer(index, dataIn, dataOut);
mailServer.start();
mailServers.add(mailServer);
dataOut.writeUTF("Client " + index);
index += 1; // add one every time a new client is added
}
}
public static void main(String[] args) throws Exception {
Server s = new Server(port);
System.out.println("Serving....");
s.serve();
}
}
Have a static list of all the MailServer objects you create
static List<MailServer> servers=Collections.<MailServer>synchronizedList(new LinkedList<MailServer>);
...
MailServer s=new MailServer(index, dataIn, dataOut);
servers.add(s);
s.start();
Then loop through them all when one of them receives a message, and for all expect the receiver, write the message to their output.
The big problem in your code is that dataOut and dataIn are unique! You need to move them to the MailServer class. Each MailServer talks to one specific client and hence needs to have their own streams.
static class MailServer extends Thread {
DataOutputStream dataOut;
DataInputStream dataIn;
And your notification loop becomes:
for(MailServer mailServer:mailServers){
if (mailServer!=this){
mailServer.dataOut.writeUtf(...);
}
}
I also don't understand how you expect to get the Client.name in the server, since Client runs on another machine... Get rid of that for now.
I am having a problem implementing a simple multi threaded server in Java.
My idea is for a server to broadcast a message to all clients(without the use of a multicast).
For this I am implementing a broadcast method. This method will use a for loop, and loop through each client Thread, which I have stored in a collection. It will call each threads send(), which outputs writeUTF().
My problem is for 2 clients A+B.
A outputs: hello
B outputs: hi there
B will not recieve hello, and when B type again, it will the recieve A's message.Code example:
import java.net.*;
import java.io.;
import java.util.;
public class ServerThreadHandler extends Thread {
private AuctionServer server = null;
private Socket socket = null;
private String name = null;
private int ID = -1;
private DataInputStream dataIn = null;
public DataOutputStream dataOut = null;
private Thread thread;
protected static Vector handlers = new Vector();
// reason server is used here is because ian was calling a server method broadcast
// from inside the
public ServerThreadHandler(AuctionServer server, Socket socket, String name) throws IOException{
this.server = server;
this.socket = socket;
this.name = name;
dataIn = new DataInputStream( new
BufferedInputStream(socket.getInputStream()));
dataOut = new DataOutputStream(socket.getOutputStream());
}
// handles a specific client.
public void run(){
System.out.println("Server running..");
while(true){
try{
// broadcast to all clients. This will only be one client in this case.
server.broadcast(dataIn.readUTF());
int pause = (int)(Math.random() * 3000);
Thread.sleep(pause);
}
catch(IOException e){
System.out.println(e.getMessage());
}
catch(InterruptedException e){
System.out.println(e.getMessage());
}
}
}
public void send(String msg){
try{
dataOut.writeUTF(msg);
dataOut.flush();
}
catch(IOException e){
}
}
Server code:
// broadcast this to clients.
public void broadcast(String msg){
for(int i = 0; i < clientCount; i++){
clients[i].send(msg);
}
}
Where clients[] is
private ServerThreadHandler clients[] = new ServerThreadHandler[3];
I'm going to give you a rough outline, you can fill in the rest of the details:
public class Server {
private ServerSocket serverSocket;
private List<Socket> clientSockets;
// constructor(s)
private class ThreadTask implements Runnable {
private Socket clientSocket;
public ThreadTask(Socket clientSocket) {
this.clientSocket = clientSocket;
}
#Override
public void run() {
while(true) {
// read message from clientSocket
for(Socket peerSocket: clientSockets) {
// send message on peerSocket
}
}
}
}
private void acceptConnections() {
while(true) {
try {
Socket clientSocket = serverSocket.accept();
clientSockets.add(clientSocket);
Thread t = new Thread(new ThreadTask(clientSocket));
t.start();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}