I am making a server for a Chat application in Java.
The while loop is supposed to connect to new clients but the code keeps connecting to the first client repeatedly even after it has connected resulting in Bind Failed error. What should I change?
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class ServerM
{
public static void main(String args[])
{
while(true)
{
Listener l = new Listener();
l.run();
}
}
}
class Listener implements Runnable
{
static InetAddress arr[] = new InetAddress[10];
static int i = 0;
public void run()
{
try
{
ServerSocket ss = new ServerSocket(44444);
System.out.println("Waiting...");
Socket s = ss.accept();
System.out.println("Connected!\n");
DataInputStream din=new DataInputStream(s.getInputStream());
String ip = din.readUTF();
InetAddress addr = InetAddress.getByName(ip);
for(int j=0; j<=i; j++)
{
if(arr[j] == addr)
return;
}
arr[i++] = addr;
ChatThread c = new ChatThread(addr,s);//This creates a thread to allow communication with Client
c.run();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
Your problem is in the design of the solution. You are running a multiple instances of the Server Socket (and using the same port, what will end in an exception) and using this thread for getting the client connections, therefore you can only have one connection.
What you should do is, run a Thread for the Server Socket who will listen for all the connections, and then run every client instance (new Thread) in an infinite loop.
public class ServerM
{
public static void main(String args[])
{
Listener l = new Listener();
l.run();
}
}
class Listener implements Runnable
{
static InetAddress arr[] = new InetAddress[10];
static int i = 0;
public void run()
{
try
{
ServerSocket ss = new ServerSocket(44444);
System.out.println("Waiting...");
while (true) {
Socket s = ss.accept();
ClientListener clientListener = new ClientListener(s);
clientListener.run();
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
class ClientListener implements Runnable {
private Socket socket;
public ClientListener(Socket socket) {
this.socket = socket;
}
public void run() {
System.out.println("Connected!\n");
DataInputStream din=new DataInputStream(s.getInputStream());
String ip = din.readUTF();
InetAddress addr = InetAddress.getByName(ip);
for(int j=0; j<=i; j++)
{
if(arr[j] == addr)
return;
}
arr[i++] = addr;
ChatThread c = new ChatThread(addr,socket);
c.run();
}
}
You have to do this because you only need one instance of ServerSocket listening for new connections at a specific port, and then you need [1..n] client instances for handling each connection.
Catch Exception is bad practice
catch(Exception e)
{
e.printStackTrace();
}
Try to forward an custom exception (MyException.class) to the top level and handle this exception in ServerM class in try..catch. And don't forget to close socket in finally block
ss.close();
s.close();
Related
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();
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 have been asked to take this post down, and in particular the code, by a superior of mine
Problem 1: Client did not receive message
Solution: Make sure port matches sending's port
Problem 2: Could not broadcast message
Solution: Use a broadcast address
// Client REceive
DatagramSocket socket = new DatagramSocket(null);
socket.setReuseAddress(true);
socket.bind(new InetSocketAddress("127.0.0.1", 4002));
// ClientSEnd
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
socket = new DatagramSocket();
socket.setReuseAddress(true);
Just add the port number to the Datagram socket in the receive. it will work fine.
Class - ClientReceive:
DatagramSocket socket = new DatagramSocket(4001);
Set the reuse address to true ..
that will make use of the address whatever it is 4001 4002..etc
socket.setReuseAddress(true);
The problem seems to be that DatagramSocket allows you to send a datagram to a given destination. In your case you are sending to localhost, so that all messages are sent to the local machine only and not to other clients. If you want to reach all network clients should use a broadcast address or use the MulticastSocket class instead DatagramSocket.
import java.net.*;
import java.io.*;
public class ClientSend implements Runnable
{
private Thread t;
private DatagramSocket socket;
private String name;
private String sendingMessage;
private int port;
public ClientSend(int port)
{
this.port = port;
}
public void run()
{
try{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
socket = new DatagramSocket();
socket.setReuseAddress(true);
while(true)
{
sendingMessage = br.readLine();
byte sendingData[] = sendingMessage.getBytes();
InetAddress clientAddress = InetAddress.getByName("224.0.0.3");
DatagramPacket sendingPacket = new DatagramPacket(sendingData, sendingData.length, clientAddress, 4011);
socket.send(sendingPacket);
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void start()
{
t = new Thread(this);
t.start();
}
public static void main(String args[]) throws Exception
{
ClientSend CS = new ClientSend(4011);
CS.start();
}
}
import java.net.;
import java.io.;
public class ClientReceive implements Runnable
{
private Thread t;
public ClientReceive()
{
}
public void run()
{
try {
// DatagramSocket socket = new DatagramSocket(null);
MulticastSocket socket = new MulticastSocket(4011);
InetAddress group = InetAddress.getByName("10.10.222.120");
socket.joinGroup(group);
//socket.setReuseAddress(true);
//socket.bind(new InetSocketAddress("10.10.222.120", 4011));
while(true)
{
byte receivingData[] = new byte[1024];
DatagramPacket receivingPacket = new DatagramPacket(receivingData, receivingData.length);
socket.receive(receivingPacket);
String receivingMessage = new String(receivingPacket.getData(), 0, receivingPacket.getLength());
System.out.println("Received: " + receivingMessage);
}
} catch (IOException e) {
e.printStackTrace();
}
}
public void start()
{
t = new Thread(this);
t.start();
}
public static void main(String args[]) throws Exception
{
ClientReceive CR = new ClientReceive();
CR.start();
}
}
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();
}
}
}
}