I'm trying to implement a server-client socket program in Java that can support multiple clients, but my class that performs the multithreading always crashes whenever my client connects to my server.
import java.io.*;
import java.net.*;
public class ClientWorker extends Thread{
Socket cwsocket=null;
public ClientWorker(Socket cwsocket){
super("ClientWorker");
cwsocket=cwsocket;
}
public void run(){
try {
PrintWriter out = new PrintWriter(cwsocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(cwsocket.getInputStream()));
String serverinput, serveroutput="";
out.println(serveroutput);
while ((serverinput = in.readLine()) != null) {
out.println(serveroutput);
if (serveroutput.equals("Terminate"))
break;
}
out.close();
in.close();
cwsocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Whenever I create a PrintWriter object, a NullPointerException exception is thrown, and I'm not sure why it continues to happen. Below are my server and client classes. What am I doing wrong?
import java.io.*;
import java.net.*;
public class Server {
public static void main(String[]args)throws IOException{
ServerSocket serversocket=null;
final int PORT_NUM=4444;
boolean flag=true;
try{
System.out.println("Listening for connection");
serversocket=new ServerSocket(PORT_NUM);
}catch(IOException e){
System.out.println("Could not listen to port: "+PORT_NUM);
System.exit(-1);
}
while(flag){
new ClientWorker(serversocket.accept()).start();
}
System.out.println("Terminating server...");
serversocket.close();
}
}
import java.io.*;
import java.net.*;
public class Client {
public static void main(String[] args){
Socket socket=null;
PrintWriter out=null;
BufferedReader in=null;
BufferedReader userInputStream=null;
String IP="127.0.0.1";
try{
socket = new Socket(IP, 4444);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
} catch (UnknownHostException e) {
System.out.println("Unknown host:" + IP);
System.exit(1);
} catch (IOException e) {
System.out.println("Cannot connect to server...");
System.exit(1);
}
String userInput, fromServer;
try{
userInputStream = new BufferedReader(new InputStreamReader(System.in));
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("Terminate"))
break;
userInput = userInputStream.readLine();
if (userInput != null) {
System.out.println("> " + userInput);
out.println(userInput);
}
}
}catch(IOException e){
System.out.println("Bad I/O");
System.exit(1);
}
try{
out.close();
in.close();
userInputStream.close();
socket.close();
System.out.println("Terminating client...");
}catch(IOException e){
System.out.println("Bad I/O");
System.exit(1);
}catch(Exception e){
System.out.println("Bad I/O");
System.exit(1);
}
}
}
In
public ClientWorker(Socket cwsocket){
super("ClientWorker");
cwsocket=cwsocket;
}
You need to do
this.cwsocket=cwsocket;
Or rename the parameter so it doesn't shadow the member of the same name.
Related
I'm creating an "echo" server that upon receiving a message simply sends it back. I have managed to get multi-client working, but I want to make some kind of disconnect detection. I tried to get it working through sending a single character from the server, then replying with another character from the client. I couldn't get this to work, though.
How would you suggest I go about disconnect detection?
MessageServer.java
import java.net.*;
import java.io.*;
public class MessageServer {
static int clientCount = 0;
public static void main(String[] args) throws IOException {
try(ServerSocket servSocket = new ServerSocket(16384)){
while(true){
Socket socket = servSocket.accept();
addClient();
new ServerThread(socket, clientCount).start();
}
} catch(IOException e) {
System.out.println("Exception caught when trying to listen on port 16384 or listening for a connection");
System.out.println(e.getMessage());
}
}
public static void addClient(){
clientCount++;
}
}
ServerThread.java
import java.net.*;
import java.io.*;
public class ServerThread extends Thread {
private Socket cltSocket;
private BufferedReader in;
private PrintWriter out;
private int num;
public ServerThread(Socket clientSocket, int count) {
cltSocket = clientSocket;
num = count;
}
public void run() {
String input;
try {
out = new PrintWriter(cltSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(cltSocket.getInputStream()));
System.out.println("Client " + num + " connected!");
while(cltSocket.isConnected() && !cltSocket.isClosed()){
if(in.ready()){
input = in.readLine();
if(input != null && !(input.equalsIgnoreCase("exit"))){
System.out.print("New input: ");
System.out.println(input);
out.println(input);
out.flush();
} else if(input.equalsIgnoreCase("exit")){
disconnect();
}
}
}
} catch(SocketException e) {
disconnect();
} catch (IOException e) {
e.printStackTrace();
return;
}
}
public void disconnect(){
System.out.println("Client " + num + " disconnected!");
out.close();
try {
in.close();
cltSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
MessageClient.java
import java.net.*;
import java.io.*;
public class MessageClient {
public static void main(String[] args) {
if(args.length != 2) {
System.out.println("Invalid parameters! Format as: (hostname) (port)");
System.exit(1);
}
String hostname = args[0];
int port = Integer.parseInt(args[1]);
try {
Socket socket = new Socket(hostname, port);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
BufferedReader con = new BufferedReader(new InputStreamReader(System.in));
System.out.println("Connected!");
while(socket.isConnected() && !socket.isClosed()){
String output;
if(con.ready()) {
output = con.readLine();
out.println(output);
if(output.equalsIgnoreCase("exit")) {
socket.close();
}
}
if(in.ready()){
String li = in.readLine();
if(li != null) {
System.out.println(li);
}
}
}
System.out.println("Disconnected!");
con.close();
out.close();
in.close();
System.exit(0);
} catch(SocketException e) {
System.err.println("Socket error:" + e);
} catch(UnknownHostException e) {
System.err.println("Invalid host");
} catch(IOException e) {
System.err.println("IO Error: " + e);
}
}
}
There is a way to do that:
if you read the BufferedReader by calling BufferedReader.getLine() and the other side socket is gone, then you get an SocketException... that is a way to check a lost connection
I am making 2 classes for Chat server client for a project I am working on. The problem is server can see the message that sent to it(from client) and it can send those messages out to every clients BUT each client has to type in some input first if he wants to see the message from other users. I have no clue what I did wrong. Please help me out. Thanks in advance :)
Server Class
import java.net.*;
import java.util.ArrayList;
import java.io.*;
public class TestServer extends Thread
{
protected Socket clientSocket;
public static ArrayList<Socket> ConnectionArray = new ArrayList<Socket>();
public static ArrayList<String> CurrentUsers = new ArrayList<String>();
final static int PORT = 22;
public static void main(String[] args) throws IOException
{
ServerSocket serverSocket = null;
try
{
serverSocket = new ServerSocket(PORT);
System.out.println ("Connection Socket Created");
try
{
while (true)
{
System.out.println ("Waiting for Connection");
Socket sock = serverSocket.accept();
ConnectionArray.add(sock);
System.out.println("Client connected from: " + sock.getLocalAddress().getHostName());
new TestServer (sock);
}
}
catch (IOException e)
{
System.err.println("Accept failed.");
System.exit(1);
}
}
catch (IOException e)
{
System.err.println("Could not listen on port: " + PORT);
System.exit(1);
}
finally
{
try {
serverSocket.close();
}
catch (IOException e)
{
System.err.println("Could not close port: 10008.");
System.exit(1);
}
}
}
private TestServer (Socket inSock)
{
clientSocket = inSock;
start();
}
public void run()
{
System.out.println ("New Communication Thread Started");
//System.out.println ("Client connected from: " + sock.getLocalAddress().getHostName());
try {
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(),true);
BufferedReader in = new BufferedReader(new InputStreamReader( clientSocket.getInputStream()));
String inputLine;
while (true)
{
inputLine = in.readLine();
System.out.println ("Server: " + inputLine);
for(int i = 1; i <= TestServer.ConnectionArray.size(); i++)
{
System.out.println("Total Connection: " + ConnectionArray.size());
Socket TEMP_SOCK = (Socket) TestServer.ConnectionArray.get(i-1);
if (clientSocket != TEMP_SOCK)
{
PrintWriter TEMP_OUT = new PrintWriter(TEMP_SOCK.getOutputStream(), true);
TEMP_OUT.println(inputLine);
TEMP_OUT.flush();
System.out.println("Sending to: " + TEMP_SOCK.getLocalAddress().getHostName());
}
}
if (inputLine.equals("Bye."))
break;
}
out.close();
in.close();
clientSocket.close();
}
catch (IOException e)
{
System.err.println("Problem with Communication Server");
System.exit(1);
}
}
}
Client Class
import java.io.*;
import java.net.*;
public class TestClient {
public static void main(String[] args) throws IOException {
String serverHostname = new String ("127.0.0.1");
if (args.length > 0)
serverHostname = args[0];
System.out.println ("Attemping to connect to host " +
serverHostname);
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
echoSocket = new Socket(serverHostname, 22);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: " + serverHostname);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for "
+ "the connection to: " + serverHostname);
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String userInput;
System.out.println ("Type Message (\"Bye.\" to quit)");
while ((userInput = stdIn.readLine()) != null)
{
out.println(userInput);
if (userInput.equals("Bye."))
break;
System.out.println("Other user: " + in.readLine());
}
out.close();
in.close();
stdIn.close();
echoSocket.close();
}
}
You need a separate thread in the client for reading from the server without blocking on System.in;
Thread t = new Thread(() -> {
try {
while (!Thread.currentThread().isInterrupted()) {
System.out.println("Other user: " + in.readLine());
}
} catch (Exception e) {
e.printStackTrace();
}
});
t.start();
while ((userInput = stdIn.readLine()) != null)
{
out.println(userInput);
if (userInput.equals("Bye."))
break;
}
t.interrupt();
Server application and client application are running in different computers. I want to send some message from client to server. The server should receive it and display. But in my case it's not happening. Nothing happens in server computer when something is sent.
This is my client program:
import java.io.*;
import java.net.*;
public class EchoClient {
//private static final String IP="194.47.46.36";
public EchoClient() {
}
public void establish() {
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
//echoSocket = new Socket(InetAddress.getLocalHost(), 8080);
echoSocket = new Socket("195.47.46.76", 4444);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(
echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O");
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(
new InputStreamReader(System.in));
String userInput;
try {
while ((userInput = stdIn.readLine()) != null) {
out.println(userInput);
if (userInput.equals("Bye."))
break;
System.out.println("echo: " + in.readLine());
}
out.close();
in.close();
stdIn.close();
echoSocket.close();
} catch (IOException ioe) {
System.out.println("Failed");
System.exit(
-1);
}
}
}
I am using Socket and ServerSocket classes to communicate on local host
client sends a no. to server and server computes square of no. and sends back to the client
// Client Class
import java.net.*;
import java.io.*;
class SocketDemo
{
public static void main(String...arga) throws Exception
{
Socket s = null;
PrintWriter pw = null;
BufferedReader br = null;
System.out.println("Enter a number one digit");
int i=(System.in.read()-48); // will read only one character
System.out.println("Input number is "+i);
try
{
s = new Socket("127.0.0.1",10101);
pw = new PrintWriter(s.getOutputStream());
br = new BufferedReader(new InputStreamReader(s.getInputStream()));
System.out.println("Connection established, streams created");
}
catch(Exception e)
{
System.out.println("Exception in Client "+e);
}
pw.println(i);
System.out.println("Data sent to server");
String str = br.readLine();
System.out.println("The square of "+i+" is "+str);
}
}
// Server Side
import java.io.*;
import java.net.*;
class ServerSocketDemo
{
public static void main(String...args)
{
ServerSocket ss=null;
PrintWriter pw = null;
BufferedReader br = null;
int i=0;
try
{
ss = new ServerSocket(10101);
}
catch(Exception e)
{
System.out.println("Exception in Server while creating connection"+e);
}
System.out.print("Server is ready");
while (true)
{
System.out.println (" Waiting for connection....");
Socket s=null;
try
{
s = ss.accept();
System.out.println("Connection established with client");
pw = new PrintWriter(s.getOutputStream());
br = new BufferedReader(new InputStreamReader(s.getInputStream()));
i = new Integer(br.readLine());
System.out.println("i is "+i);
}
catch(Exception e)
{
System.out.println("Exception in Server "+e);
}
System.out.println("Connection established with "+s);
i*=i;
pw.println(i);
try
{
pw.close();
br.close();
}
catch(Exception e)
{
System.out.println("Exception while closing streams");
}
}
}
}
Please Help
On client side do this after sending data to server
pw.println(i);
pw.flush();
I'm having problems with broadcasting the messages sent by each client. The server can receive each message from multiple clients but it cannot broadcast it. Error message says connection refused
Client:
public void initializeConnection(){
try {
host = InetAddress.getLocalHost();
try{
// Create file
FileWriter fstream = new FileWriter("src/out.txt", true);
BufferedWriter out = new BufferedWriter(fstream);
out.write(host.getHostAddress()+'\n');
//Close the output stream
out.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
}
clientSocket = new Socket(host.getHostAddress(), port);
outToServer = new PrintWriter(clientSocket.getOutputStream(), true);
inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
}
catch(IOException ioEx) {
ioEx.printStackTrace();
}
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==quit){
try {
outToServer.close();
clientSocket.close();
System.exit(1);
} catch (IOException e1) {
e1.printStackTrace();
}
}
else if(e.getSource()==button){
if(outMsgArea.getText()!=null || !outMsgArea.getText().equals("")){
String message = outMsgArea.getText();
outToServer.println(clientName+": "+message);
outMsgArea.setText("");
}
}
}
public void run(){
try {
while(true){
String message = inFromServer.readLine();
System.out.println(message);
inMsgArea.append(message+'\n');
}
} catch (IOException e) {
e.printStackTrace();
}
}
Server:
import java.io.*;
import java.net.*;
import java.util.*;
public class RelayChatServer {
public static int port = 44442;
ServerSocket server;
public void listenSocket(){
try{
server = new ServerSocket(port);
} catch (IOException e) {
System.out.println("Could not listen on port 4444");
System.exit(-1);
}
while(true){
ClientWorker w;
try{
//server.accept returns a client connection
w = new ClientWorker(server.accept());
Thread t = new Thread(w);
t.start();
} catch (IOException e) {
System.out.println("Accept failed: 4444");
System.exit(-1);
}
}
}
protected void finalize(){
//Objects created in run method are finalized when
//program terminates and thread exits
try{
server.close();
} catch (IOException e) {
System.out.println("Could not close socket");
System.exit(-1);
}
}
public static void main(String[] args) {
new RelayChatServer().listenSocket();
}
}
class ClientWorker implements Runnable {
private Socket client;
//Constructor
ClientWorker(Socket client) {
this.client = client;
}
public void run(){
String line;
BufferedReader in = null;
PrintWriter out = null;
try{
in = new BufferedReader(new
InputStreamReader(client.getInputStream()));
//out = new
// PrintWriter(client.getOutputStream(), true);
} catch (IOException e) {
System.out.println("in or out failed");
System.exit(-1);
}
while(true){
try{
line = in.readLine();
//Send data back to client
//out.println(line);
//Append data to text area
if(line!=null && line!=""){
System.out.println(line);
try{
// Open the file that is the first
// command line parameter
FileInputStream fstream = new FileInputStream("out.txt");
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
String strLine;
//Read File Line By Line
Socket s;
PrintWriter prnt;
while ((strLine = br.readLine()) != null && (strLine = br.readLine()) != "") {
// Print the content on the console
s = new Socket(strLine, 44441);
prnt = new PrintWriter(s.getOutputStream(),true);
prnt.println(line);
System.out.println(strLine);
prnt.close();
s.close();
}
//Close the input stream
//inp.close();
}catch (Exception e){//Catch exception if any
System.err.println("Error: " + e.getMessage());
}
}
}catch (IOException e) {
System.out.println("Read failed");
e.printStackTrace();
System.exit(-1);
}
}
}
}
The Exception starts:
java.net.ConnectException: Connection refused: connect
The expanded output looks like:
I'm somewhat confused as to why you attempt to open a new socket (do you intend for this to be sent back to the client?) based on a string you read from a file. Perhaps
s = new Socket(strLine, 44441);
prnt = new PrintWriter(s.getOutputStream(),true);
should be:
prnt = new PrintWriter(client.getOutputStream(),true);
As currently I don't see where you are sending anything back to the client.
Edit: ok try something like the following:
static final ArrayList<ClientWorker> connectedClients = new ArrayList<ClientWorker>();
class ClientWorker implements Runnable {
private Socket socket;
private PrintWriter writer;
ClientWorker(Socket socket) {
this.socket = socket;
try {
this.writer = new PrintWriter(socket.getOutputStream(), true);
} catch (IOException ex) { /* do something sensible */ }
}
public void run() {
synchronized(connectedClients) {
connectedClients.add(this);
}
BufferedReader in = null;
try {
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
} catch (IOException e) { /* do something sensible */ }
while (true) {
try {
String line = in.readLine();
if (line != null && line != "") {
synchronized (connectedClients) {
for (int i = 0; i < connectedClients.size(); ++i){
ClientWorker client = connectedClients.get(i);
client.writer.println(line);
}
}
}
} catch (IOException e) { /* do something sensible */ }
}
}
}