Develop Reference

Chat server client sometimes cannot see message from other clients on the same server

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-client communication by using IP address doesn't work

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);
}
}
}

iterative dictionary server in java

what it do..
1. an iterative dictionary server that is listening clients requests..
2. connection will be established..
3. server will accept input string from client..
4. then server will search meaning of string from a file..
5. then server will return meaning to the client..
problem is with the while loop of server.. if it finds word it will send that word's meaning to client..fine.. but if word is not found... this
if(d.equals(null)){
input="No knowledge";
out.println(input);
out.flush();
}
doesn't execute... client says null and server says null exception...
what i am doing wrong here... i'm not getting it...!!
i have tried to changed this code...
client-server online dictionary program in java
client:
import java.io.;
import java.net.;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;
public class DCC1 {
public static void main(String[] args) throws IOException {
final int PORT = 8888;
Socket s = null;
PrintWriter out = null;
try {
s = new Socket("localhost", PORT);
out = new PrintWriter(s.getOutputStream()); // Output stream to the server
}
catch (UnknownHostException ex) {
System.err.println("Unknown host: " + PORT);
System.err.println("Exception: " + ex.getMessage());
System.exit(1);
}
catch (IOException ex) {
System.err.println("Cannot get I/O for " + PORT);
System.err.println("Exception: " + ex.getMessage());
System.exit(1);
}
Scanner user = new Scanner(System.in); // Scanning for user input
System.out.print("Enter String: ");
String input;
input = user.next(); // Hold the input from the user
out.println(input); // Send it to the server
out.flush();
BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream( )));
System.out.println(br.readLine());
out.close();
s.close();
}
}
server:
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Scanner;
public class DSC1
{
public static void main(String[] args) throws IOException
{
final int PORT = 8888;
final String FILE_NAME = "dictionary.dat";
ServerSocket server = new ServerSocket(PORT);
Socket s = null;
PrintWriter out = null;
Scanner in = null;
FileInputStream fin = null;
ObjectInputStream oin = null;
while (true)
{
try
{
s = server.accept();
}
catch (IOException ex)
{
System.err.println("Accept failed");
System.err.println("Exception: " + ex.getMessage());
System.exit(1);
}
System.out.println("Accepted connection from client");
try
{
in = new Scanner(s.getInputStream()); // Input stream from the client
out = new PrintWriter(s.getOutputStream()); // Output stream to the client
String temp = in.next(); // String holding the word sent from the client
System.out.println("From the client " + temp);
String input = null;
fin = new FileInputStream(FILE_NAME);// The dictionary file
oin = new ObjectInputStream(fin);
dictionary d = (dictionary)oin.readObject();
while(d!= null)
{
System.out.println("in loop...");
if(d.name.equals(temp)){
input=d.meaning;
d.printDic();
out.println(input);
out.flush();
break;
}
d = (dictionary)oin.readObject();
if(d.equals(null))
{
input="No knowledge";
out.println(input);
out.flush();
}
}
}
catch (ClassNotFoundException|IOException ex)
{
System.err.println("Exception: " + ex.getMessage());
System.out.println("Closing connection with client");
in.close();
System.exit(1);
}
in.close();
}
}
}

Don't use d.equals(null). If you want to check if d is null, just do if (d==null).
Why? There's no way this can return true, so probably that's the reason why this code never executes and you don't get what you expect.

Cannot send commands via Sockets

I'm new to the world of Java and now I'm trying to create a socket program. I created a server and a client, but they didn't seem to work. Now I post the code.
This is the server:
import java.net.*;
import java.io.*;
public class TCPCmdServer
{
public int port;
public ServerSocket server;
TCPCmdServer (int port)
{
this.port = port;
if(!createServer())
System.out.println("Cannot start the server");
else System.out.println("Server running on port " + port);
}
public boolean createServer ()
{
try
{
server = new ServerSocket(port);
}
catch (IOException e)
{
e.printStackTrace();
return false;
}
return true;
}
public static void main (String [] args)
{
TCPCmdServer tcp = new TCPCmdServer(5000);
boolean flag = true;
while (flag)
{
try
{
Socket socket = tcp.server.accept();
System.out.println("A client has connected");
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
out.write("Welcome on the server... type the commands you like, type END to close me\n");
out.flush();
String cmd = in.readLine();
System.out.println("Recieved: " + cmd);
if (cmd.equals("END"))
{
System.out.println("Shutting down server...");
socket.close();
in.close();
out.close();
flag = false;
}
else
{
Process p = Runtime.getRuntime().exec(cmd);
BufferedReader pRead = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line;
while ((line = pRead.readLine()) != null)
{
System.out.println(line);
out.write(line + "\n");
out.flush();
}
}
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}
}
And this is the client:
import java.net.*;
import java.io.*;
public class TCPCmdClient
{
public Socket socket;
public int port;
public String ip;
TCPCmdClient (String ip, int port)
{
this.ip = ip;
this.port = port;
if (!createSocket())
System.out.println("Cannot connect to the server. IP: " + ip + " PORT: " + port);
else System.out.println("Connected to " + ip + ":" + port);
}
public boolean createSocket ()
{
try
{
socket = new Socket(ip, port);
}
catch (IOException e)
{
e.printStackTrace();
return false;
}
return true;
}
public static void main (String [] args)
{
TCPCmdClient client = new TCPCmdClient("127.0.0.1", 5000);
try
{
BufferedReader sysRead = new BufferedReader(new InputStreamReader(System.in));
BufferedReader in = new BufferedReader(new InputStreamReader(client.socket.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(client.socket.getOutputStream()));
String response = in.readLine();
System.out.println("Server: " + response);
boolean flag = true;
while (flag)
{
System.out.println("Type a command... type END to close the server");
String cmd = sysRead.readLine();
out.write(cmd + "\n");
out.flush();
if (cmd.equals("END"))
{
client.socket.close();
sysRead.close();
in.close();
out.close();
flag = false;
} else
{
String outputline;
while ((outputline = in.readLine()) != null)
System.out.println(outputline);
}
}
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}
[old]
I believe the problem is with the input and output streams, but I can't understand why they don't work.
The expected behavior is as follows: The client connects to the server then the server send response. The client asks the user to insert a MS-DOS command (or a "END" command), the command is then sent to the server. The server executes the command on the computer where it is running (in case the command is END it closes the connection). Then the server sends the result of the command to the client, and the client displays it to the user.
[/old]
Now the only problem is that I have to close and re-open a client any time I like to execute a new command

In your server code, you are creating a new socket for every command you received from the client. That is why you have to open a new client every time you want to send a command to the server. To correct this, first you need to remove the while(flag) loop in server code. Then you can use the following to establish the connection to the client and send and receive command and output between them.
Socket socket = tcp.server.accept();
System.out.println("A client has connected");
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
out.write("Welcome on the server... type the commands you like, type END to close me\n");
out.flush();
try {
while(!(cmd = in.readLine()).equals("END")) {
System.out.println("Recieved: " + cmd);
Process p = Runtime.getRuntime().exec(cmd);
BufferedReader pRead = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line;
while ((line = pRead.readLine()) != null) {
System.out.println(line);
out.write(line + "\n");
out.flush();
}
}
} catch (IOException ex) {
ex.printStackTrace();
} finally {
System.out.println("Shutting down server...");
socket.close();
in.close();
out.close();
}

In TCPCmdServer.java, try changing
out.write("Welcome on the server... type the commands you like, type END to close me");
to
out.write("Welcome on the server... type the commands you like, type END to close me\n");
out.flush();
Also, change
out.write(buffer.toString());
to
out.write(buffer.toString() + "\n");
out.flush();
In TCPCmdClient.java
change
out.write(cmd);
to
out.write(cmd + "\n");
out.flush();
response = in.readLine();
System.out.println("Server: " + response);

Socket Timeout Issue: android client reading data from pc server

I'm new to android, java and socket programming so of course I'm trying to merge all three!
I'm creating a desktop based java server which will simply send a short string to an android app(client).
I have the android app running fine and it sends strings to the server which are read with no problems.
I have the server running and it recieves the strings with no problems.
The app(client) however has a socket timeout whenever I try to read the strings returned from the server. I'm using the same code so I can't understand the problem.
Anyway here's the code:
//SERVER//
import java.io.*;
import java.net.*;
import java.util.*;
public class GpsServer {
ServerSocket serversocket = null;
Socket socket = null;
public GpsServer()
{
try
{
serversocket = new ServerSocket(8189);
}
catch (UnknownHostException unhe)
{
System.out.println("UnknownHostException: " + unhe.getMessage());
}
catch (InterruptedIOException intioe)
{
System.out.println("Timeout while attempting to establish socket connection.");
} catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
}
public void refreshServer() {
try
{
socket = serversocket.accept();
InputStreamReader inputstreamreader = new InputStreamReader(socket.getInputStream());
BufferedReader bufferedreader = new BufferedReader(inputstreamreader);
PrintWriter printwriter = new PrintWriter(socket.getOutputStream(),true);
System.out.println("socket read successful");
printwriter.println("Send Bye to disconnect.");
String lineread = "";
boolean done = false;
while (((lineread = bufferedreader.readLine()) != null) && (!done)){
System.out.println("Received from Client: " + lineread);
printwriter.println("You sent: " + lineread);
if (lineread.compareToIgnoreCase("Bye") == 0) done = true;
}
System.out.println("Closing connection");
socket.close();
bufferedreader.close();
inputstreamreader.close();
printwriter.close();
}
catch (UnknownHostException unhe)
{
System.out.println("UnknownHostException: " + unhe.getMessage());
}
catch (InterruptedIOException intioe)
{
System.out
.println("Timeout while attempting to establish socket connection.");
}
catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
}
public void nullify() {
try
{
socket.close();
serversocket.close();
}
catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
}
}
and the client...
//CLIENT
import java.io.*;
import java.net.*;
import java.util.*;
public class GpsClient {
public String lastMessage;
Socket socket = null;
String serverurl;
int serverport;
public GpsClient() {
lastMessage = "";
serverport = 8189;
serverurl = "192.168.10.4";
try
{
socket = new Socket(serverurl, serverport);
socket.setSoTimeout(10000);
}
catch (UnknownHostException unhe)
{
System.out.println("UnknownHostException: " + unhe.getMessage());
}
catch (InterruptedIOException intioe)
{
System.out.println("Timeout while attempting to establish socket connection.");
}
catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
}
public void retrieveNew() {
try {
socket = new Socket(serverurl, serverport);
socket.setSoTimeout(10000);
lastMessage = "connected!";
InputStreamReader inputstreamreader = new InputStreamReader(socket.getInputStream());
BufferedReader bufferedreader = new BufferedReader(inputstreamreader);
PrintWriter printwriter = new PrintWriter(socket.getOutputStream(),true);
printwriter.println("Request");
lastMessage = "Request sent";
// Get error when I uncomment this block, i.e. try to read the response from the server
// "Timeout while attempting to establish socket connection."
// String lineread = "";
// while ((lineread = bufferedreader.readLine()) != null) {
// System.out.println("Received from Server: " + lineread);
// lastMessage = "Received from Server: " + lineread;
// }
lastMessage = "closing connection!";
bufferedreader.close();
inputstreamreader.close();
printwriter.close();
socket.close();
}
catch (UnknownHostException unhe)
{
System.out.println("UnknownHostException: " + unhe.getMessage());
}
catch (InterruptedIOException intioe)
{
System.out.println("Timeout while attempting to establish socket connection.");
}
catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
finally
{
try
{
socket.close();
}
catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
}
}
public void nullify() {
try
{
PrintWriter printwriter = new PrintWriter(socket.getOutputStream(),true);
printwriter.println("Bye");
printwriter.close();
socket.close();
}
catch (IOException ioe)
{
System.out.println("IOException: " + ioe.getMessage());
}
}
}
Thanks in advance!
Josh

Apart from all the issues noted in my comment, you are creating two sockets in the client, and your server is only written to process one connection. So it writes to the first one and tries to read from it, meanwhile your client is writing to the second one and trying to read from that.
When you fix that you will then hit a deadlock, as both sides are trying to read from each other.
Also you shouldn't use PrintWriter or PrintStream over the network, as they swallow exceptions you need to know about. Use BufferedWriter.

Try putting something at the end of the server message, like ETX or something like <end> or wrap the message in <msg>...</msg>.
Then on Android in the while loop check if you received it instead of checking (lineread = bufferedreader.readLine()) != null.