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Java Sockets - Client message not reaching Server

currently I am trying to send multiple messages from a client to a server and echo them on the server but somehow my message is not arriving at the server until i press CTRL+Z(D) and hit enter.
My loop runs as long as the user does not enter "quit" but altough I write my message to the OutputStream and flush it my message does not show on the Server side as if my Client still reads input.
(I do not want to use BufferedReaders or Threads at the moment it's purely for learning reasons.)
Would be nice if someone could tell me where my mistake/error lies.
Read also the javadocs but still can not find my mistake.
Client.java
public class Client {
//class members
private String msg = null;
private Scanner scn = null;
public Client(String ip, int port) throws IOException {
//Connect to Server
try(Socket socket = new Socket(ip,port))
{
//Initialize class members
scn = new Scanner(System.in); //Init Scanner
msg="";
System.out.println("Enter message:");
//Write to Socket
OutputStream out = socket.getOutputStream();
while(!msg.equals("quit"))
{
msg=scn.nextLine();
out.write(msg.getBytes(), 0, msg.length());
out.flush();
}
}
catch (IOException ex)
{
System.err.println(ex);
}
}
Server.java
public class Server {
//class members
private String msg = null;
public Server(int port) throws IOException {
//Setup ServerSocket.
ServerSocket server = new ServerSocket(port);
System.out.println("SERVER: Launched service.");
//Accept incoming connection requests.
while(true) {
try(Socket connection = server.accept())
{
System.out.println("SERVER: Client connection accepted.");
//Read Input
StringBuilder line = new StringBuilder();
InputStream in = connection.getInputStream();
for(int c=in.read(); c!=-1; c=in.read())
{
line.append((char) c);
}
System.out.println(line);
}
catch (IOException ex)
{
System.out.println("SERVER: Client disconnected!");
}
}
}
sincerely,
rhyleigh

Your server prints nothing until read() returns -1.
read() returns -1 at end of stream.
Over a TCP socket, end of stream is only caused by the peer closing the connection.
Your server's peer, i.e. the client, doesn't close the connection until you type ^Z at the terminal. which causes an unstated exception to be thrown.
Your program is working as designed.

Can't send multiple messages via socket

I'm trying to make a little chat system. I have a console and a client. Right now only the client need to send messages to the console. I can connect successfully to the server, and i can send one message from client to console. The trouble begins after sending the first message. When the first message i can't send any other messages.
I don't know if it's the console that won't read the message or the client that won't send the message. In this case how could i troubleshoot this?
public class ClientMainClass {
private static Socket socket;
public static void main(String args[]) {
try {
String host = "localhost";
int port = 25000;
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);
Scanner scanner = new Scanner(System.in);
System.out.println("Skriv dit username:");
String name = scanner.nextLine();
System.out.println("Du er logget ind som: " + name);
String input;
do{
input = scanner.nextLine();
if (input.equalsIgnoreCase("exit")) {
System.out.println("Du forlod serveren");
socket.close();
continue;
}else {
/*OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);*/
PrintWriter printWriter = new PrintWriter(socket.getOutputStream(),true);
Date date = new Date();
String time = date.getDate()+"/"+date.getMonth()+":"+date.getHours()+":"+date.getMinutes();
//Send the message to the server
String message = time+ " - " + name + ": "+input;
printWriter.println(message);
System.out.println(message);
continue;
}
}while (!(input.equals("exit")));
} catch (Exception exception) {
exception.printStackTrace();
} finally {
//Closing the socket
try {
socket.close();
} catch(Exception e) {
e.printStackTrace();
}
}
}
}
My server:
public class Main{
private static Socket socket;
public static void main(String[] args) {
try {
int port = 25000;
ServerSocket serverSocket = new ServerSocket(port);
System.out.println("Server Started and listening to the port 25000");
while(true) {
//Reading the message from the client
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
System.out.println(br.readLine());
}
}
catch (Exception e) {
e.printStackTrace();
} finally {
try {
socket.close();
} catch(Exception e){}
}
}
}
To be clear. I can connect to the server. I can send one message from client to console, but no more than one message.

You never read a second line. Your Server accepts a connection, reads one line from that connection and then waits for a new connection, discarding everything that might arrive at the first connection.
Your client however sends all input using the first (and only) connection, which is absolutely correct.
This specific problem can be solved like this:
while(true) {
//Reading the message from the client
socket = serverSocket.accept();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
while(true){
System.out.println(br.readLine());
}
}
This will cause your program to print everything arriving on that first connection, but it will never accept a second connection.
In order to handle multiple clients, you need a Thread to deal with each one.

java Simple Server Client program

I'm trying to build a simple server client program, I'm trying to figure a way how to prompt the CLIENT if the server is down, or if the server is up and loses connection
Question: How can I prompt the client that he's disconnected because the Server shuts down or loses connection
SERVER
public class Server{
private static Socket socket;
public static void main(String[] args)
{
try
{
int port = 25000;
ServerSocket serverSocket = new ServerSocket(port);
//Server is running always. This is done using this while(true) loop
while(true)
{
//Reading the message from the client
socket = serverSocket.accept();
System.out.println("Client has connected!");
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String number = br.readLine();
System.out.println("Message received from client is "+number);
//Multiplying the number by 2 and forming the return message
String returnMessage;
try
{
int numberInIntFormat = Integer.parseInt(number);
int returnValue = numberInIntFormat*2;
returnMessage = String.valueOf(returnValue) + "\n";
}
catch(NumberFormatException e)
{
//Input was not a number. Sending proper message back to client.
returnMessage = "Please send a proper number\n";
}
//Sending the response back to the client.
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
bw.write(returnMessage);
System.out.println("Message sent to the client is "+returnMessage);
bw.flush();
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
CLIENT
public class Client{
private static Socket socket;
public static void main(String args[])
{
Scanner input=new Scanner(System.in);
while(true)
{
try
{
String host = "localhost";
int port = 25000;
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);
//System.out.println("You're now connected to the Server"); /*this should only print once */
//Send the message to the server
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
String number;
number=input.next();
String sendMessage = number + "\n";
bw.write(sendMessage);
bw.flush();
System.out.println("Message sent to the server : "+sendMessage);
//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " +message);
}
catch (IOException exception)
{
//System.out.println("Server is still offline");/*This should only print once*/
}

How can I prompt the client that he's disconnected because the Server shuts down or loses connection?
You can use the catch block to prompt the client in Client class which will be executed when IOException occurs
} catch (ConnectException e) { //When the connection is refused upon connecting to the server
//promt the user here
System.out.println("Connection refused");
break; //to quit the infinite loop
} catch (IOException e) { //when connection drops, server closed, loses connection
//promt the user here
System.out.println("Disconnected from server");
break; //to quit the infinite loop
}

How to use UDP with multiple Clients in Java

I have the following Situation.
I have a Server class.
I have a Client class.
I have a MultiServerThread class.
When a Client connects to a Server, the Server creates a new MultiServerThread, which is processing the Input from the Client. That way I can have multiple Clients. So far so good.
The connection goes via TCP.
A short example:
Server class:
...
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
boolean listening = true;
try {
serverSocket = new ServerSocket(9999);
} catch (IOException e) {
System.err.println("Could not listen on port: " + serverSocket.getLocalPort() + ".");
System.exit(-1);
}
while (listening) {
new MultiServerThread(serverSocket.accept()).start();
}
serverSocket.close();
}
...
Client class:
...
public static void main(String[] args) throws IOException {
socket = new Socket(hostname, port);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("Bye.")) {
break;
}
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
out.close();
in.close();
stdIn.close();
socket.close();
}
...
MultiServerThread class:
...
public MultiServerThread(Socket socket) throws SocketException {
super("MultiServerThread");
this.socket = socket;
// dSocket = new DatagramSocket(4445);
}
public void run() {
try {
PrintWriter myOutput = new PrintWriter(socket.getOutputStream(), true);
BufferedReader myInput = new BufferedReader(new InputStreamReader(socket.getInputStream()));
myOutput.println("Connected to client and ready to accept commands.");
while ((clientInput = myInput.readLine()) != null) {
//A SIMPLE LOGIN A USER
if (clientInput.contains("!login")) {
//save some string given by client into loggedUser
String loggedUser = clientInput.substring(7);
}
myOutput.close();
myInput.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
What I need is:
I need to implement a notification that comes from a Server when for example the Username is "Bob". If the username is "Bob", the server should give a notification to the Client "Bob is here again!". In my project/homework this should be done with datagrams in Java.
So if the clientinput is "!login bob" then a datagram packet with the message ("Bob is here again!") should be sent to the client.
Question: Where exactly should I put the code of the Datagram request in? Can I put the datagram packet request into the MultiServerThread or into the Client?
It would be easier in the MultiServerThread because it already handles the !login.
Here:
if (clientInput.contains("!login")) {
//save some string given by client into loggedUser
String loggedUser = clientInput.substring(7);
//send datagram request to Server???
}
But this is going against the principle of networking?

you need to send the UDP port number to your client through the initial TCP connection. Then you start listening for UDP datagrams on your client on that port number. All other communications from server -> client will be on this udp socket. This is what your assignment suggests

I got it working ;-)
I definied a udp port in the thread and client class...
the client class got his port with arguments... it gave the udp Port to the thread... so both had the udp ports ;)

Cannot communicate with server in Java

I am trying to write server to client program but I cannot communicate with the server in Java.
Here is the code block in my main.
InetAddress addr = InetAddress.getLocalHost();
ipAddress = "78.162.206.164";
ServerSocket serverSocket = new ServerSocket(0);
String randomStringForPlayerName = RandomStringGenerator.generateRandomString();
baseForReqOpp += ipAddress + " " + serverSocket + " " + randomStringForPlayerName;
Socket socket = new Socket(host,2050);
socket.setSoTimeout(100);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out = new PrintWriter(socket.getOutputStream());
out.write(baseForReqOpp);
out.flush();
System.out.println(in.read());
I know that there is no problem in the server code and all the communication ports are ok.
But I cannot read anything from the server.
What can be the problem?

you have to create an output stream before the input stream

Here is some working code with communicating client and server sockets. Hopefully you can adapt it for your specific problem.
public class SocketTest {
public void runTest() {
try {
// create the server
new SimpleServer().start();
// connect and send a message
InetAddress addr = InetAddress.getLocalHost();
Socket sock = new Socket(addr, 9090);
ObjectOutputStream out = new ObjectOutputStream(sock.getOutputStream());
out.writeObject("Hello server");
out.flush();
ObjectInputStream in = new ObjectInputStream(sock.getInputStream());
System.out.println("from server: " + in.readObject());
sock.close();
} catch (Exception e) {
e.printStackTrace();
}
}
// server has to run in a separate thread so the code doesn't block
private class SimpleServer extends Thread {
#Override
public void run() {
try {
ServerSocket sock = new ServerSocket(9090);
Socket conn = sock.accept();
// the code blocks here until a client connects to the server
ObjectInputStream in = new ObjectInputStream(conn.getInputStream());
System.out.println("from client: " + in.readObject());
ObjectOutputStream out = new ObjectOutputStream(conn.getOutputStream());
out.writeObject("Hello client");
out.flush();
sock.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
To run it:
new SocketTest().runTest();

Your code will never work because you don't use threads. In order to start the server, you need to call accept at some point in your code
myServerSocket.accept();
this is a blocking call, ie the code flow stops until a client connects. But since you can't execute any statement (remember accept is blocking?) how can a client connect? This chicken and egg problem is resolved through threads. See Howard's answer for a code sample.
I don't see any call to accept(), so I wonder what your client connects to...