Hello programmers on the internet. I am currently stepping through an operating systems book and there are some exercises that involve the following pieces of code.
This is the server code
import java.net.*;
import java.io.*;
public class DateServer{
public static void main(String[] args) {
try {
ServerSocket sock = new ServerSocket(6013);
// now listen for connections
while (true) {
Socket client = sock.accept();
PrintWriter pout = new
PrintWriter(client.getOutputStream(), true);
// write the Date to the socket
pout.println(new java.util.Date().toString());
// close the socket and resume
// listening for connections
client.close();
}
}
catch (IOException ioe) {
System.err.println(ioe);
}
}
}
This is the client code
import java.net.*;
import java.io.*;
public class DateClient{
public static void main(String[] args) {
try {
//make connection to server socket
Socket sock = new Socket("127.0.0.1",6013);
InputStream in = sock.getInputStream();
BufferedReader bin = new
BufferedReader(new InputStreamReader(in));
// read the date from the socket
String line;
while ( (line = bin.readLine()) != null)
System.out.println(line);
// close the socket connection
sock.close();
}
catch (IOException ioe) {
System.err.println(ioe);
}
}
}
So to my understanding the server is creating a socket and writing a date value to it. The client is then coming a long and connecting to the server and writing out the value in that socket. Am I interpreting this code correctly? This is my first experience with sockets.
Now for my actual question. I want to have the client connect to the server (and print out a message saying you are connected) and then be able to send a value over to the server so that the server can process it. How would I go about doing this? I have tried tinkering with DataOutputStream and DataInputStream but I have never used either before. Any help would be GREATLY appreciated.
You are correct. You have the server writing to the socket and the client reading from the socket. You want to reverse that.
Server Should look like:
ServerSocket sock = new ServerSocket(6013);
// now listen for connections
while (true)
{
Socket client = sock.accept();
InputStream in = client.getInputStream();
BufferedReader bin = new BufferedReader(new InputStreamReader(in));
// read the date from the client socket
String line;
while ((line = bin.readLine()) != null)
System.out.println(line);
// close the socket connection
client.close();
}
The client should look like:
try
{
// make connection to server socket
Socket sock = new Socket("127.0.0.1", 6013);
PrintWriter out = new PrintWriter(sock.getOutputStream(), true);
// send a date to the server
out.println("1985");
sock.close();
}
catch (IOException ioe)
{
System.err.println(ioe);
}
Related
I have written a simple Java TCP Server and a Client (See below).
The idea is quite simple: the Client sends a message to the Server the Server reads it, modify it and sends it back to the client.
import java.io.*;
import java.net.*;
public class ServerTest2 {
public static void main(String[] argv) {
try {
ServerSocket serverSocket = new ServerSocket(2000); // Create Socket and bind to port 2000
System.out.println("Created");
Socket clientSocket = serverSocket.accept(); //Wait for client and if possible accept
System.out.println("Connection accepted");
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream())); // for outputs
BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); // for inputs
String request; // requst/input of client
String answer; // the answer for the client
System.out.println("Start Waiting");
request = br.readLine(); //Wait for input from client
answer = "answer to "+request;
bw.write(answer); // Send answer to client
System.out.println("send");
bw.newLine();
bw.flush();
//Shut everything down
bw.close();
br.close();
clientSocket.close();
serverSocket.close();
}
catch (Exception e) {
System.out.println(e);
}
}
}
The Client Implementation
import java.io.*;
import java.net.*;
public class ClientTest2 {
public static void main(String[] argv) {
try {
String host = "185.75.149.8"; //public ip of router
Socket clientSocket = new Socket(host,2000); //Create and connect Socket to the host on port 2000
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream())); // for outputs
BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); // for inputs
String answer;
String request = "HelloWorld";
bw.write(request); //Write to server
bw.newLine();
bw.flush();
System.out.println("Waiting");
answer = br.readLine(); //Wait for answer
System.out.println("Host = "+host);
System.out.println("Echo = "+answer);
//Shut eveything down
bw.close();
br.close();
clientSocket.close();
}
catch (Exception e) {
System.out.println(e);
}
}
}
It works perfectly on my local network.
Now I want to use it via the Internet so I installed Port Forwarding on Port 2000 in my Router which sends it to Port 2000 of my PC.
My PC is directly connected to my Router without any Subnets in between.
The Problem is that the Server does not accept the connection(Stops at serverSocket.accept()).
It does not throw an Exception it just waits forever.
The Client does also not throw an Exception (If the Port isn't open it would throw a Connection refused Exception)
This means that the Port Forwarding should work (I have also tested whether the port is open with a Webtool (its open)).
But strangely the Client stops waiting after about 10 seconds and continues with the program.
Since the Port Forwarding should work and my Code works fine in my local Network I absolutely don't know how or where I could find the problem.
I appreciate any help.
Thank you very much!
EDIT: A poorly researched question, written when I was in a rush-it has nothing to do with socket.accept()-see below for accepted answer.Please no more downvoting.
I'm new to socket programming and in my toy 'Server' class I'm not getting any lines from the peer:
public class Server {
private ServerSocket myServerSocket;
String messageFromClient=null;
private void startServer(){
try{
myServerSocket=new ServerSocket(2000);
int portUsed= myServerSocket.getLocalPort();
System.out.println(portUsed);
Socket mySocket=myServerSocket.accept();
System.out.println("accepted");
InputStreamReader streamFromClient = new InputStreamReader(mySocket.getInputStream());
BufferedReader streamReader= new BufferedReader(streamFromClient);
messageFromClient=streamReader.readLine();
System.out.println("current message:"+messageFromClient);
if(messageFromClient!=null){
PrintStream ps = new PrintStream(mySocket.getOutputStream());
ps.print("Thank you client, I gratefully received from your message-hi from server!");
}
}
catch(Exception e){
e.printStackTrace();
}
}
for completeness, here is the client class:
public class Client {
#SuppressWarnings("resource")
private void startClient(){
try{
Socket socket = new Socket("localhost",2000);
PrintStream ps = new PrintStream(socket.getOutputStream());
ps.print("hi from client");
InputStreamReader inputStreamReader=new InputStreamReader(socket.getInputStream());
BufferedReader reader=new BufferedReader(inputStreamReader);
System.out.println("From Server:"+reader.readLine());
}
catch(Exception e){
e.printStackTrace();
}
}
They both have main methods. Any help would be very much appreciated thanks you!
You need to use println instead of all prints. As an explanation, while your server is waiting for an end of line character your client never sends. And it is same for when your server sends a message.
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 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 ;)
I have a question, I'm currently working on a little project of mine and stumbled upon a dead end. I have a Java Server :
import java.io.*;
import java.net.*;
class TCPServer
{
public static void main(String argv[]) throws Exception
{
ServerSocket welcomeSocket = new ServerSocket(3443);
Socket clientSocket =null;
ClientHandler ch;
while(true)
{
try{
clientSocket = welcomeSocket.accept();
System.out.println("Client connected on port :"+clientSocket.getPort());
ch = new ClientHandler (clientSocket);
Thread t = new Thread(ch);
t.start();
}catch (Exception e){
System.out.println("SERVER CRASH");
}
}
}
}
Then the client connects through the port 3443, a new thread is created with ClientHandler. Now is the problem, in the client side the socket used to connect is still on port 3443, but on the server side the thread is on an arbitrary port, let's say 5433, so the server can communicate with the thread but not the client, because it has no knowledge of what port the thread is using... I'm a bit confused with all this, does the client class is only needed to make the initial connection, then all the communication is done through the ClientHandler class, if so should i also instantiate an object of ClientHandler in the client class?
Here's my client class :
import java.io.*;
import java.net.*;
class TCPClient
{
static Socket clientSocket = null;
public static void main(String argv[]) throws Exception
{
BufferedReader k = new BufferedReader(new InputStreamReader(System.in));
BufferedReader ine = null;
DataOutputStream oute = null;
try{
clientSocket = new Socket("localhost", 3443);
oute = new DataOutputStream(clientSocket.getOutputStream());
ine = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
} catch (UnknownHostException e) {
System.out.println("Unknown host");
System.exit(1);
} catch (IOException e) {
System.out.println("No I/O");
System.exit(1);
}
try{
//send
oute.writeBytes(k.readLine());
//recieve
String line = ine.readLine();
System.out.println("Text received: " + line);
} catch (IOException e){
System.out.println("Read failed");
System.exit(1);
}
}
}
The problem is the socket created in client is still connected to Port 3443, and the server is listening to this port, so I won't recieve anything from the server (infinite loop). The clientHandler is on another port. Am i doing it wrong?
You’re calling accept() twice. Call it only once and store the resulting Socket in a variable that you can then hand in to new ClientHandler().
Oh, also, the Socket knows both sides of the communication so it won’t be confused by whatever port the client uses.