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.
Related
I am playing around with networking and trying to send a simple message over my network using sockets in Java.
Here is the server code:
public class Server {
public static void main(String[] args) throws IOException {
String clientSentence;
String uppercaseSentence;
ServerSocket welcomeSocket = new ServerSocket(6789);
System.out.println("Server Running.");
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
clientSentence = inFromClient.readLine();
System.out.println("Client message received: " + clientSentence);
}
Here is the client code:
public class Client {
public static void main(String[] args) throws IOException {
String originalSentence;
String modifiedSentence;
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("localhost", 6789);
System.out.println("Please enter a sentence: ");
originalSentence = inFromUser.readLine();
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
outToServer.writeBytes(originalSentence);
System.out.println("Message Sent");
}
When I run them both and input a message into the client side, there is no confirmation on the side of the server in the console, however there is confirmation on the client side that a message has been sent. If I then end the client and stop it running, the server will output the sent message to the console them immediately throw an error.
I think it has something to do with the actual BufferedReader not actually getting the message or something?
Again I am very new to networking so any help would be much appreciated
Make sure that there is symmetry in how one connection sends data and how the other side receives the data. So, if the client is sending data via a DataOutputStream, then best to read the data in as a DataInputStream. If OTOH, you're only sending Strings, I would use a Writer such as a PrintWriter and then read with a Reader. I would send each line via println(...) and would call .flush() on the PrintWriter to ensure that the buffer sends the line when desired. For example, a simple client could look like so:
import java.util.*;
import java.net.*;
import java.io.*;
public class Client {
public static final String EXIT = "exit";
public static final int HOST_ID = 6789;
public static void main(String[] args) {
// using try-with-resources so that I close all streams when done
try (
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("localhost", HOST_ID);
PrintWriter out = new PrintWriter(clientSocket.getOutputStream());
) {
String input = "";
do {
System.out.print("Please enter a sentence, or \"exit\" to exit: ");
input = inFromUser.readLine();
out.println(input);
// flush the output stream to send all pending bites:
out.flush();
} while (!input.equalsIgnoreCase(EXIT));
System.out.println("All Done");
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
and the Server could look like:
import java.util.*;
import java.net.*;
import java.io.*;
public class Server {
public static void main(String[] args) {
// using try-with-resources so that I close all streams when done
try (
ServerSocket welcomeSocket = new ServerSocket(6789);
Scanner scanner = new Scanner(welcomeSocket.accept().getInputStream());
) {
System.out.println("Server Running.");
System.out.println("socket accepted");
while (scanner.hasNextLine()) {
String text = scanner.nextLine();
System.out.println("text: " + text);
System.out.println("uppercase: " + text.toUpperCase());
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
I'm trying to program a Server Client program where the CLIENT will be prompt if the SERVER closes or loses connection. What happens is once I connect the server and the client then disconnects the server it doesn't go to the ConnectException part
example: I opened the Server and Client connects, in the Client it will show that "You are connected to the Server", then if the Server disconnects there should be a "Server is disconnected". and when the Server reopens it will prompt the Client that he's connected to the Server
How can I continuously check if the Server is open or disconnected
here's my code:
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);
try
{
String host = "localhost";
int port = 25000;
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);
System.out.println("Connected to the Server");
}
catch (ConnectException exception)
{
System.out.println("Server is still offline");
}
catch(IOException ex)
{
System.out.println("Server got disconnected");
}
}
}
Well, the best way to tell if your connection is interrupted is to try to read/write from the socket. If the operation fails, then you have lost your connection sometime.
So, all you need to do is to try reading at some interval, and if the read fails try reconnecting.
The important events for you will be when a read fails - you lost connection, and when a new socket is connected - you regained connection.
That way you can keep track of up time and down time.
you can do like this
try
{
Socket s = new Socket("address",port);
DataOutputStream os = new DataOutputStream(s.getOutputStream());
DataInputStream is = new DataInputStream(s.getInputStream());
while (true)
{
os.writeBytes("GET /index.html HTTP/1.0\n\n");
is.available();
Thread.sleep(1000);
}
}
catch (IOException e)
{
System.out.println("connection probably lost");
e.printStackTrace();
}
or you can simply et connection time out like this socket.setSoTimeout(timeout); to check connectivity
or you can use
socket.getInputStream().read()
makes the thread wait for input as long as the server is connected and therefore makes your program not do anything - except if you get some input and
returns -1 if the client disconnected
or what you can do is structure your code in this way
while(isConnected())
{
// do stuffs here
}
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
}
I'm learning java. I'm trying to make a simple client/server chat system. What I have so far is a program where the server accepts multiple client connections by giving them each a seperate thread.
My problem now, is that I can't figure out how to get an input from one client, and then have it be sent amongst all of the clients, thus essentially have a very very simple chat mechanic. How would I go about accomplishing this? What would be the simpler way?
My code so far is here;
class Client {
public static void main(String argv[]) throws Exception {
String sentMessage; //variable for input
String receivedMessage; //variable for output
String status;
boolean running;
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("127.0.0.1", 5622); //name of computer to connect with and port number to use
DataOutputStream outToServer =
new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer =
new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
System.out.println("Client Side\n");
running = true;
while(running)
{
sentMessage = inFromUser.readLine(); //user inputs text to variable 'xInput'
outToServer.writeBytes(sentMessage + '\n'); //the variable is sent to the server
status = inFromServer.readLine();
System.out.println("FROM SERVER: " + status); //display to user
}
clientSocket.close();
}
}
The server code.
class Server {
public static void main(String argv[]) throws Exception {
String clientMessage;
boolean listening = true;
int portNumber = 5622;
try (ServerSocket serverSocket = new ServerSocket(portNumber)) {
while (listening) {
new ServerThread(serverSocket.accept()).start();
}
} catch (IOException e) {
System.err.println("Could not listen on port " + portNumber);
System.exit(-1);
}
}
}
The thread that handles the client connections.
public class ServerThread extends Thread {
private Socket socket = null;
public ServerThread(Socket socket) {
super("ServerThread");
this.socket = socket;
}
public void run () {
int msgCnt = 0;
try (
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(
socket.getInputStream()));
) {
//something needs to go here
} catch (IOException e) {
e.printStackTrace();
}
}
If you are looking for a simple client-server communication samples then please have a look at below posts where I have described it step by step.
Multiple clients access the server concurrently
Java Server with Multiclient communication.
So I did this client server program in java for my college mini project. Note that this is just a small module of a big project I'm working on. I need a string to be sent from the client to the server. The server will return back the string as it is back to the client. (The code will be modified later such that the string is processed before sending back). The client will send a string whenever needed to the server. Thus it means it is compulsory for the server to be running for indefinite time.
The problem I face here is that my server works perfectly only for the first time when the client sends a string. If I run the client the second time with a different string, I get back the same string I sent to the server previously!
Here is my server program:
public class Server {
public static boolean x = true;
public static String reply;
public static void main(String a[]) throws Exception {
System.out.println("Entered server console..");
Socket echoSocket = null;
ServerSocket serverSocket = null;
PrintWriter out = null;
BufferedReader in = null;
System.out.println("Initializing Connection..");
boolean runFlag = true;
try {
serverSocket = new ServerSocket(77);
while (runFlag) {
echoSocket = serverSocket.accept();
out = new PrintWriter(echoSocket.getOutputStream(), true);
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
while (x) {
in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
reply = in.readLine();
if (reply != null) {
x = false;
}
}
System.out.println("received: " + reply);
out.println(reply);
System.out.println("sent back: " + reply);
stdIn.close();
}
} catch (Exception e) {
System.out.println("Exception in starting server: " + e.getMessage());
} finally {
out.close();
in.close();
echoSocket.close();
}
}
}
Here is my Client program:
public class Client {
public static String reply,temp;
public static boolean x=true;
public Client()
{
temp="lala";
}
public Client(String t)
{
temp=t;
}
public static void main(String[] args) throws IOException {
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
echoSocket = new Socket("localhost", 77);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: localhost.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: localhost.");
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
temp="lala"; //this is the string to be sent
out.println(temp);
while (x) {
reply= in.readLine();
if(reply!=null)
{
x=false;
}
}
System.out.println("reply: "+reply);
out.close();
in.close();
stdIn.close();
echoSocket.close();
}
}
Can anyone help me find what the problem here is?
while (x) {
in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
reply = in.readLine();
if (reply != null) {
x = false;
}
}
Your server enters this loop the first time a client connects, and it sets the reply String to some input from the client. However, it never enters this loop again, as x's value never changes back to true.
When you accept a request, the x will be set false and never become true.
Please initial the x when you enter the loop.
What's more,if you use a socket between client and server, please move the
echoSocket = serverSocket.accept();
out of the first loop.And you can use echoSocket to communicate.Then you will
keep the long connection.