Develop Reference

TCP client and server, cmd prompt using objectstreams

I have one client file clientRPC.java and server file serverRPC.java. Both communicate using TCP protocol and use objectinput and output stream to transfer data.
my client file:
public class clientRPC {
public static void main(String args[]) {
Socket s = null;
try {
int serverPort = 8888;
s = new Socket("localhost", serverPort);// server name is local host
//initializing input and output streams object and referencing them to get input and output
ObjectInputStream in = null;
ObjectOutputStream out = null;
out = new ObjectOutputStream(s.getOutputStream());
in = new ObjectInputStream(s.getInputStream());
MathsTutor mt = new MathsTutor();
out.writeObject(mt);
out.flush();
System.out.println("Welcome to Maths Tutor Service. The available maths exercises are:\n"
+ "Addition: Enter 'A' or 'a'\n"
+ "Subtraction: Enter 'S' or 's'\n"
+ "Multiplication: Enter 'M' or 'm'\n"
+ "Division: Enter 'D' or 'd'\n"
+ "Enter 'Q' or 'q' to quit");
//System.out.println();
MathsTutor mt1 = (MathsTutor) in.readObject();
String response = in.readUTF();
System.out.println(response);
} catch (UnknownHostException e) {
System.out.println("Socket:" + e.getMessage());
} catch (EOFException e) {
System.out.println("EOF:" + e.getMessage());
} catch (IOException e) {
System.out.println("readline:" + e.getMessage());
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
} finally {
if (s != null) {
try {
s.close();
} catch (IOException e) {
System.out.println("close:" + e.getMessage());
}
}
}
}
}
and my server file :
public class serverRPC extends Thread {
String request;
String response;
public static void main(String args[]) {
try {
int serverPort = 8888;
ServerSocket listen_socket = new ServerSocket(serverPort);
while (true) {
Socket clientSocket = listen_socket.accept();
Connection c = new Connection(clientSocket);
}
} catch (IOException e) {
System.out.println("Listen socket:" + e.getMessage());
}
public serverRPC(String s) {
request = s;
}
}
class Connection extends Thread {
ObjectInputStream in;
ObjectOutputStream out;
Socket clientSocket;
public Connection(Socket aClientSocket) {
try {
clientSocket = aClientSocket;
in = new ObjectInputStream(clientSocket.getInputStream());
out = new ObjectOutputStream(clientSocket.getOutputStream());
this.start();
} catch (IOException e) {
System.out.println("Connection:" + e.getMessage());
}
}
public void run() {
try {
MathsTutor mt = (MathsTutor) in.readObject();
InetAddress ip = clientSocket.getInetAddress();
System.out.println("The Received Message from Client at address:/" + ip.getHostAddress());
System.out.println("====================================");
MathsTutor mt1 = new MathsTutor();
out.writeObject(mt1);
while(true) {
// Read from input
String command = in.readUTF();
System.out.println(command);
}
//System.out.println();
} catch (EOFException e) {
System.out.println("EOF:" + e.getMessage());
} catch (IOException e) {
System.out.println("readline:" + e.getMessage());
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
} finally {
try {
clientSocket.close();
} catch (IOException e) {/*close failed*/
}
}
}
}
The problem is when I run server and then client on cmd, the client side displays the welcome msg and puts cursor on another line for user input but, I can't type anything, the cursor just blinks... I know this might be simple but it has taken already 3 hours for me and I'm stuck in the same thing.
The cursor marked with red keeps blinking but doesn't let me type anything.

You're writing an object with writeObject() and trying to read it with readUTF(). Illogical.
objects written with writeObject() must be read with readObject().
strings written with writeUTF() must be read with readUTF().
primitives written with writeXXX() must be read with readXXX(), for most values of X.

client creates new socket object everytime the server is on

i've done a socket programming with client residing on android and server residing on the desktop ....... whenever server is down as we know client lost the connection.....so it undergoes a looping until it connects to server.......
here the problem is in the below code
tabletclient = new Socket(SERVER_IP, TAB_SERVER_PORT);
in the while loop in the case of lost connection.........but when the connection is on it again creates a new object........
can anyone please tell me how to solve this problem..........
In the client side
while(true){
try {
tabletclient = new Socket(SERVER_IP, TAB_SERVER_PORT);
tabletout = new PrintWriter(tabletclient.getOutputStream());
in = new Scanner(tabletclient.getInputStream());
try
{
if((line = in.nextLine())!=null)
{
// my task to be done
}
}catch(Exception d){
System.out.println("Connection from server has lost.........tabletclient.isConnected()----->"+tabletclient.isConnected());
}
} catch (UnknownHostException e) { System.out.println("Entered 2.........");
} catch (IOException e) { System.out.println("Entered 3.........");e.printStackTrace();
}
}
In in the Server side
:
:
private Set <Socket> TABhs=new HashSet<Socket>();
:
:
new Thread(new TABServerThread()).start(); // runs in background
:
:
:
class ServerThread implements Runnable {
private ServerSocket server;
#Override
public void run() {
try {
server = new ServerSocket(SERVER_PORT);
System.out.println("Server Start the server at port " + SERVER_PORT
+ " and waiting for clients...");
while (true) {
Socket socket = server.accept();
System.out.println("Server Accept socket connection: "
+ socket.getLocalAddress());
new Thread(new ClientHandler(socket)).start();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
private static PrintWriter out;
class ClientHandler implements Runnable {
private Socket clientSocket;
private Scanner in;
public ClientHandler(Socket clietSocket) {
this.clientSocket = clietSocket;
}
#Override
public void run() {
try {
out = new PrintWriter(clientSocket.getOutputStream());
in = new Scanner(clientSocket.getInputStream());
String line;
System.out.println("ClientHandlerThread Start communication with : "+ clientSocket.getLocalAddress());
try{
while((line = in.nextLine()) != null) {
System.out.println("ClientHandlerThread Client says: " + line);
String dat[]=line.split("#");
String query="insert into table_orders (tableno,kotno, orders,status) values('"+dat[1]+"','"+dat[0]+"','"+dat[2]+"','pending')";
try {
int i= dbGetDet.insertDetails(query);
if(i>0)
{
fillTable();
filtercomboBox();
out.print("success");
out.flush();
for(Socket so:TABhs)
{
PrintWriter ot = new PrintWriter(so.getOutputStream());
ot.println("tableallocation#"+dat[1]);
ot.flush();
}
System.out.println("SENDED 'SUCCESS' TO CLIENT");
}
} catch (Exception ex) {
Logger.getLogger(MYClientclass.class.getName()).log(Level.SEVERE, null, ex);
}
// }
}
}catch(Exception r){}
} catch (IOException e) {
e.printStackTrace();
}
}
}
In the Button click of server
String stat=status_combo.getSelectedItem().toString();
String tables=tableno_combo.getSelectedItem().toString();
String kotno=kotno_combo.getSelectedItem().toString();
if(stat.equals("Processing"))
{
try {
TABhs = new CopyOnWriteArraySet(TABhs);
int soint=1;
System.out.println("TABhs Processing--------------------->"+TABhs.size());
for(Iterator <Socket> it=TABhs.iterator();it.hasNext();)
{
Socket so=it.next();
System.out.println("SEEE SOCKET Processing"+soint+"----->"+so.isClosed());
PrintWriter ot = new PrintWriter(so.getOutputStream());
ot.println("tableupdate#"+tables+"#"+kotno+"#processing");
ot.flush();
JOptionPane.showMessageDialog(rootPane, "<html><body>Table Kot Status Changed to <b>Processing</b></body></html>");
soint++;
}
System.out.println("TABhs Processing--------------------->"+TABhs.size());
}
catch (Exception ex) {
Logger.getLogger(MYClientclass.class.getName()).log(Level.SEVERE, null, ex);
}
}
NOW EACH TIME WHEN BUTTON IS CLICKED THE OUTPUT IS AS GIVEN BELOW
FISRT CLICK
SEEE SOCKET Ready 1----->false
Server Accept socket connection: /192.168.1.74
SEEE SOCKET Ready 2----->false
TABhs--------------------->2
SECOND CLICK
SEEE SOCKET Ready 1----->false
SEEE SOCKET Ready 2----->false
Server Accept socket connection: /192.168.1.74
SEEE SOCKET Ready 3----->false
TABhs--------------------->4
FOURTH CLICK
SEEE SOCKET Ready 1----->false
SEEE SOCKET Ready 2----->false
SEEE SOCKET Ready 3----->false
Server Accept socket connection: /192.168.1.74
SEEE SOCKET Ready 4----->false
TABhs--------------------->5

I think the problem is at the client's side you read a line and then create a new connection.
I think you must keep reading the socket until it's closed or an error occurs.
For example:
while (true)
{
tabletclient = null;
int loop = 0;
// loop until a connection is established
while (tabletclient == null)
{
try
{
tabletclient = new Socket(SERVER_IP, TAB_SERVER_PORT);
}
catch (Exception e)
{
e.printStackTrace();
// set the value to quit when no connection could be established
if (loop++ > 100)
return;
}
}
try
{
tabletout = new PrintWriter(tabletclient.getOutputStream());
in = new Scanner(tabletclient.getInputStream());
// read the socket until it's closed or an error occurs
try
{
while ((line = in.nextLine()) != null)
{
// my task to be done
}
}
catch (Exception d)
{
System.out.println("Connection from server has lost.........tabletclient.isConnected()----->"
+ tabletclient.isConnected());
}
tabletsocket.close();
}
catch (UnknownHostException e)
{
System.out.println("Entered 2.........");
}
catch (IOException e)
{
System.out.println("Entered 3.........");
e.printStackTrace();
}
}
Also, you must close the server side when the transfer from the server to the client is completed.

Using a ServerSocket without port forwarding?

This may be a stupid question, but here goes.
Im writing this chat program, where there is a server, and clients that can connect to it. I want to implement private messaging into the program, but I don't know how to get the clients to directly connect to eachother. For the server, I used a ServerSocket, which runs on a single port. To get that to work, I needed to forward a port to the server. Is there a way to get the clients to wait for connections, without forwarding a port to them?
Thanks

The whole point of TCP/IP is that a single client connects to a predefined port on a server. So yes, you'll also need to have a ServerSocket on the client that's going to accept the direct connection. You'll almost always run into trouble with port forwarding and the like, which is why UPnP was invented one day.
What you are trying to do is 'peer to peer' connectivity, aka P2P, which is always, by its very definition, plagued by firewalling problems. As such it's usually, especially for a chat, easier to use the central server as 'switchboard' server and relay the private messages as well.

I've written not long time ago a template for multiple client - server application, that might help you to solve your problem. The rest of your question was already answerd by #Niels, I think ;)
import java.net.*;
import java.io.*;
class ServeConnection extends Thread {
private Socket socket = null;
private BufferedReader in = null;
private PrintWriter out = null;
public ServeConnection(Socket s) throws IOException {
// init connection with client
socket = s;
try {
in = new BufferedReader(new InputStreamReader(
this.socket.getInputStream()));
out = new PrintWriter(this.socket.getOutputStream(), true);
} catch (IOException e) {
System.err.println("Couldn't get I/O.");
System.exit(1);
}
start();
}
public void run() {
System.out.println("client accepted from: " + socket.getInetAddress()
+ ":" + socket.getPort());
// get commands from client, until is he communicating or until no error
// occurs
String inputLine, outputLine;
try {
while ((inputLine = in.readLine()) != null) {
System.out.println("request: " + inputLine);
outputLine = inputLine;
out.println("I've recived "+outputLine);
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("server ending");
out.close();
try {
in.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
class Server {
public static void svr_main(int port) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(port);
} catch (IOException e) {
System.err.println("Could not listen on port: " + port);
System.exit(1);
}
System.out.println("Server ready");
try {
while (true) {
Socket socket = serverSocket.accept();
try {
new ServeConnection(socket);
} catch (IOException e) {
System.err.println("IO Exception");
}
}
} finally {
serverSocket.close();
}
}
}
class Client {
static Socket echoSocket = null;
static PrintWriter out = null;
static BufferedReader in = null;
public static void cli_main(int port, String servername) throws
IOException {
try {
echoSocket = new Socket(servername, port);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(
echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: " + servername);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for " + servername);
System.exit(1);
}
System.out.println("Client ready!");
while (true) {
inputLine = (in.readLine().toString());
if (inputLine == null) {
System.out.println("Client closing!");
break;
}
// get the input and tokenize it
String[] tokens = inputLine.split(" ");
}
out.close();
in.close();
echoSocket.close();
System.out.println("Client closing");
}
}
public class MyClientServerSnippet{
public static void main(String[] args) throws IOException {
if (args.length == 0) {
System.err.println("Client: java snippet.MyClientServerSnippet<hostname> <port>");
System.err.println("Server: java snippet.MyClientServerSnippet<port>");
System.exit(1);
}
else if (args.length > 1) {
System.out.println("Starting client...\n");
Client client = new Client();
client.cli_main(3049, "127.0.0.1");
} else {
System.out.println("Starting server...\n");
Server server = new Server();
server.svr_main(3049);
}
}
}

communication between groovy and java programs through sockets

I am trying to write a small socket program with client side in groovy and the server side in Java. Below is the code I wrote
client:
def s = new Socket("localhost", 4444);
s << "Server before withStreams\n";
s.withStreams { input, output ->
println"Sending message1"
output << "server message1\n"
}
s.close();
server:
import java.io.*;
import java.net.*;
public class Logger{
ServerSocket providerSocket;
Socket connection = null;
BufferedReader in;
String message="InitialMessage";
Logger(){}
void run()
{
try{
providerSocket = new ServerSocket(4444, 10);
try{
Thread.sleep(1000);
}
catch(InterruptedException ie)
{
System.out.println("Sleep Interrupted");
}
System.out.println("Waiting for connection");
connection = providerSocket.accept();
System.out.println("Connection received from " + connection.getInetAddress().getHostName());
in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
do{
if(in.ready())
{
try{
System.out.println(in.read());
message = in.readLine();
System.out.println("client>" + message);
}
catch(IOException e)
{
System.out.println(e);
e.printStackTrace();
break;
}
}
} while(!message.equals("bye"));
}
catch(IOException ioException){
ioException.printStackTrace();
}
finally{
//4: Closing connection
try{
in.close();
providerSocket.close();
}
catch(IOException ioException){
ioException.printStackTrace();
}
}
}
public static void main(String args[])
{
Logger server = new Logger();
while(true){
server.run();
}
}
}
When I execute both programs, Socket communication is established. But I get a IOException in server code when it reads from the socket (message = in.readLine();)
I guess there is some format problem in writing into socket in client. But not able to figure out the exact problem. Can anybody help?

You generally don't want to close your ServetSocket for each client connection. You want to do this once (or every time you start the server) then on each accept() handle the client connection and close the socket for that connection but keep the ServerSocket open until you want to stop the server.
Here's a rewritten version of your example server that also creates a new Thread for each client request to handle multiple concurrent requests. Note that since the test client doesn't send the terminating string "bye" the connection and socket stays open.
import java.io.*;
import java.net.*;
public class Logger {
private ServerSocket providerSocket;
Logger() {
}
public void start() {
try {
providerSocket = new ServerSocket(4444, 10);
while (true) {
System.out.println("Waiting for connection");
Socket connection = providerSocket.accept();
new Thread(new Job(connection)).start();
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (providerSocket != null) {
System.out.println("Stopping server");
try {
providerSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
static class Job implements Runnable {
final Socket connection;
private static int id;
private int clientId = ++id;
public Job(Socket connection) {
this.connection = connection;
}
public void run() {
BufferedReader in = null;
try {
System.out.println("Connection " + clientId + " received from " + connection.getInetAddress().getHostName());
in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String message = "InitialMessage";
do {
if (in.ready()) {
try {
// not sure why want to read one character then read the line
//int ch = in.read();
//System.out.println(ch);
// -1 if the end of the stream has been reached
//if (ch == -1) break;
message = in.readLine();
// null if the end of the stream has been reached
if (message == null) break;
System.out.println("client>" + message);
} catch (IOException e) {
System.out.println(e);
e.printStackTrace();
break;
}
}
} while (!message.equals("bye"));
} catch (IOException e) {
e.printStackTrace();
} finally {
//4: Closing connection
System.out.println("Close connection " + clientId);
if (in != null)
try {
in.close();
} catch (IOException ioException) {
ioException.printStackTrace();
}
try {
connection.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
public static void main(String args[]) {
Logger server = new Logger();
server.start();
}
}

Java, problem sending a message with socket connection

I have a problem with my Java program. It has a socket connection between a server and many client. Here is the server (the part which concerns the problem):
private static ArrayList<ParallelServer> clientConnected = new ArrayList<ParallelServer>();
public Server(int port) {
this.port = port;
if (!startServer())
JOptionPane.showMessageDialog(new JFrame(""),
"Error!", "ERROR!",
JOptionPane.ERROR_MESSAGE);
}
private boolean startServer() {
try {
server = new ServerSocket(port);
loadDatabase();
} catch (IOException ex) {
ex.printStackTrace();
return false;
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
return true;
}
public void runServer() {
while (true) {
try {
client = server.accept();
ParallelServer pServer = new ParallelServer(client);
clientConnected.add(pServer);
Thread thread = new Thread(pServer);
thread.start();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
public static void sendBroadcast(String username) throws IOException {
for(int i = 0; i < clientConnected.size(); i++)
clientConnected.get(i).sendAnswer("#change," + username);
}
The parallel server is:
private Socket client;
private InputStreamReader inputstreamreader;
private BufferedReader bufferedreader;
private PrintWriter printwriter;
public ParallelServer(Socket client) {
this.client = client;
}
public void run() {
try {
inputstreamreader = new InputStreamReader(client.getInputStream());
bufferedreader = new BufferedReader(inputstreamreader);
printwriter = new PrintWriter(client.getOutputStream(), true);
String lineread = "";
while (client.isConnected()) {
lineread = bufferedreader.readLine();
doCommand(lineread);
}
} catch (UnknownHostException unhe) {
} catch (InterruptedIOException intioe) {
} catch (IOException ioe) {
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public void sendAnswer(String answer) throws IOException {
printwriter = new PrintWriter(client.getOutputStream(), true);
printwriter.println(answer);
printwriter.flush();
}
And here is the client:
private String serverurl = "localhost";
private int serverport = 7777;
private PrintWriter printwriter;
private InputStreamReader inputstreamreader;
private BufferedReader bufferedreader;
private Socket server;
public Client() {
server = null;
try {
server = new Socket(serverurl, serverport);
server.setSoTimeout(5000);
} 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) {
JOptionPane.showMessageDialog(new JFrame(),"Unable to reach the server!","ERROE!",JOptionPane.ERROR_MESSAGE);
}
}
public String sendCommand(String command) throws IOException {
if(server == null) {
try {
server = new Socket(serverurl, serverport);
server.setSoTimeout(5000);
} 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) {
JOptionPane.showMessageDialog(new JFrame(),"Unable to reach the server!","ERROR!",JOptionPane.ERROR_MESSAGE);
}
}
if(server != null) {
printwriter = new PrintWriter(server.getOutputStream(), true);
printwriter.println(command);
printwriter.flush();
inputstreamreader = new InputStreamReader(server.getInputStream());
bufferedreader = new BufferedReader(inputstreamreader);
return bufferedreader.readLine();
}
else
return "#serverProblem";
}
The program is a simple online game with turns. Players' turns are created with a queue and when a player passes his turn, the server send a broadcast message which say "Now it is 'Player 1' turn." (for instance). My problem is that when a client receive the message, its like it add the answer "Now it is 'Player 1' turn." to the next message it will receive. In my case: when a player passes his turn, he sends "#passTurn,username". The ParallelServer class polls it from the queue, puts it at the bottom of the queue, sends the client "#ok" to tell it that the turn has changed successfully and tells the Server class to send the broadcast message. Then, when the same client will try do do a further action, it will consider "Now it is 'Player 1' turn." as the answer the server has given to it. Instead, I would like that the server and the clients work as always and when the broadcast message is cought, the client is notified without any collateral effect.
What can I do?
Thanks.

Your bi-directional message passing mechanism should look something like this:
Server:
Wait on any client InputStream
if (broadcast)
broadcast_message()
else
process_message()
Client:
Receiving Thread:
Wait on server broadcast
Sending Thread:
Wait on messages to be sent to server from the User Input
This should do the trick :)
Hope it helps. Cheers!