We Keep Coding

ObjectInputStream is not able to recognize my Object Data format

I am getting EOFException from the following code:
if (!(in.read() == -1))
{
CANDataInfo canData = (CANDataInfo) in.readObject();
System.out.println(canData.toString());
bw.write(canData.toString());
}
else
{
System.out.println("in.read() == -1 "+in.readObject());
jLab0x28.setText("No more bytes to read ");
}
I am doing an Socket programming where server is sending continuos data to client at some interval. The Data whichis passed from server to client in via socket is of type CANDataInfo object which i have developed. At client side while i am printing the data i am getting exception. Since object's read is always -1 i am not able to log the data on some file.
Server Side Code:
private ServerSocket server = null;
private Socket client = null;
private ObjectOutputStream out;
public static final String TAG = "APP1";
private void structureData(CANDataInfo canDataInfo)
{
try
{
if(server == null)
{
server = new ServerSocket(38301);
server.setSoTimeout(0);
}
client = server.accept();
Log.e("Server ", ""+client.isConnected());
Log.e("Data ", ""+canDataInfo.toString());
if(!client.isConnected())
{
Log.e("Server ", "client.isConnected() "+client.isConnected());
server.close();
}
out = new ObjectOutputStream(client.getOutputStream());
out.writeObject(canDataInfo);
out.close();
}
catch (Exception ex)
{
Log.e(CANManagerSetUp.TAG, "" + ex);
}
}
Client Side Code {Not a clean solution, Refer Answer from EJP}
package com.cnh.socket.client;
import java.io.BufferedWriter;
import java.io.EOFException;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.net.Socket;
import javax.swing.JLabel;
import cantest.setup.CANDataInfo;
public class ThreadListener
{
Socket client = null;
ObjectInputStream in = null;
ListenFor0X28 runnableListenFor0X28 = null;
boolean continueMe;
public class ListenFor0X28 implements Runnable
{
JLabel jLab0x28;
public ListenFor0X28(){}
public ListenFor0X28(boolean stop, JLabel jLab0x28)
{
continueMe = stop;
this.jLab0x28 = jLab0x28;
}
public void run()
{
while(continueMe)
{
try
{
client = new Socket("localhost", 38301);
in = new ObjectInputStream(client.getInputStream());
if(client.isConnected())
{
jLab0x28.setText("Connected to Server");
appendFile(continueMe, jLab0x28, client);
}
else
{
System.out.println("Client is trying to connect");
jLab0x28.setText("Client is trying to connect");
}
}
catch(Exception ex)
{
ex.printStackTrace();
System.err.println("Before Append "+ex.toString());
}
}
}
}
BufferedWriter file = getFile("C:\\ISSUE124_Resolved.txt");
private void appendFile(boolean continueMe, JLabel jLab0x28, Socket client)
{
try
{
if(!client.isClosed())
{
try
{
CANDataInfo canData = (CANDataInfo) in.readObject();
System.out.println(canData.toString());
file.write(canData.toString());
file.flush();
}
catch (EOFException exp)
{
continueMe = true;
System.out.println("A Stream has finished "+exp.toString()+"\n");
}
catch (ClassNotFoundException exp)
{
exp.printStackTrace();
System.err.println(exp.toString());
continueMe = false;
}
}
if(!continueMe)
{
file.close();
client.close();
in.close();
jLab0x28.setText("Socket is closed "+client.isClosed());
}
}
catch(IOException exp)
{
exp.printStackTrace();
System.err.println("Exception "+exp.toString());
jLab0x28.setText(exp.getMessage());
continueMe = false;
}
}
public BufferedWriter getFile(String path)
{
try
{
File file = new File(path);
if (!file.exists())
{
file.createNewFile();
}
FileWriter fw = new FileWriter(file.getAbsoluteFile());
return new BufferedWriter(fw);
}
catch (IOException e)
{
e.printStackTrace();
}
return null;
}
}
Exception Stack: {Before Resolving}
java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at com.cnh.socket.client.ThreadListener.appendFile(ThreadListener.java:73)
at com.cnh.socket.client.ThreadListener.access$0(ThreadListener.java:65)
at com.cnh.socket.client.ThreadListener$ListenFor0X28.run(ThreadListener.java:48)
at java.lang.Thread.run(Unknown Source)
Data received in unknown format java.io.EOFException

In the client
if (!(in.read() == -1))
{
CANDataInfo canData = (CANDataInfo) in.readObject();
System.out.println(canData.toString());
bw.write(canData.toString());
}
The first line reads one byte from the input stream. This is actually the first byte of the object that was written by the server. Thus the stream is no longer aligned correctly so the following readObject() fails.

You should remove the pointless and erroneous read() call, which is getting your object streams out of sync.
While you're at it, you can also remove all the redundant calls to isConnected(). They aren't doing anything. You seem to have a mania for calling extra methods which mostly don't do anything, or which try to predict the future. Try to taper off.
EDIT As requested I am critiquing not only your client but your server code.
Server:
private void structureData(CANDataInfo canDataInfo)
{
try
{
if(server == null)
The ServerSocket should have been created and configured in the constructor.
{
server = new ServerSocket(38301);
server.setSoTimeout(0);
Zero is the default. Don't assert defaults. Remove.
}
client = server.accept();
Log.e("Server ", ""+client.isConnected());
Logging isConnected() is redundant. Remove. This will always print true. The socket is connected. You just accepted it. If you want to log something useful, log the client socket's remote address.
Log.e("Data ", ""+canDataInfo.toString());
How can there be any data when you haven't read any yet? If this is invariant server-side data, why log it on every accept?
if(!client.isConnected())
{
Log.e("Server ", "client.isConnected() "+client.isConnected());
server.close();
}
This test can never pass, and the code block can never be entered, and if by some miracle it was entered, closing the server socket is a ridiculous response. Remove all this.
out = new ObjectOutputStream(client.getOutputStream());
out.writeObject(canDataInfo);
out.close();
}
catch (Exception ex)
Don't catch Exception. Catch IOException.
{
Log.e(CANManagerSetUp.TAG, "" + ex);
You should log the exception class, its message, and the stack trace. ""+ex does not accomplish that.
}
}
Client:
public class ThreadListener
{
Socket client = null;
ObjectInputStream in = null;
ListenFor0X28 runnableListenFor0X28 = null;
boolean continueMe;
public class ListenFor0X28 implements Runnable
{
JLabel jLab0x28;
public ListenFor0X28(){}
public ListenFor0X28(boolean stop, JLabel jLab0x28)
{
continueMe = stop;
this.jLab0x28 = jLab0x28;
}
public void run()
{
while(continueMe)
{
try
{
client = new Socket("localhost", 38301);
in = new ObjectInputStream(client.getInputStream());
if(client.isConnected())
The client is connected. You just connected it, when you constructed the Socket. And if by some miracle it wasn't connected, calling getInputStream() would already have failed with a SocketException. Remove this test. In general there is far too much testing of things that can't be true or can't be false in your code.
{
jLab0x28.setText("Connected to Server");
appendFile(continueMe, jLab0x28, client);
}
else
{
System.out.println("Client is trying to connect");
jLab0x28.setText("Client is trying to connect");
}
}
The else block is unreachable, and the log message 'Client is trying to connect' is incorrect. Remove the entire block and the else.
catch(Exception ex)
See above. Don't catch Exception. Catch the exceptions the compiler tells you to catch: in this case IOException and the DNS-related ones.
{
ex.printStackTrace();
System.err.println("Before Append "+ex.toString());
See above about how to log exceptions.
}
}
}
}
BufferedWriter file = getFile("C:\\ISSUE124_Resolved.txt");
private void appendFile(boolean continueMe, JLabel jLab0x28, Socket client)
{
try
{
if(!client.isClosed())
{
try
{
CANDataInfo canData = (CANDataInfo) in.readObject();
System.out.println(canData.toString());
file.write(canData.toString());
file.flush();
}
catch (EOFException exp)
{
continueMe = true;
System.out.println("A Stream has finished "+exp.toString()+"\n");
}
catch (ClassNotFoundException exp)
{
exp.printStackTrace();
System.err.println(exp.toString());
continueMe = false;
}
}
if(!continueMe)
{
file.close();
client.close();
in.close();
You don't need to close both the input stream and the socket. Either will do. General practice is to close the outermost writer/output stream if there is one, otherwise the input stream.
jLab0x28.setText("Socket is closed "+client.isClosed());
}
}
catch(IOException exp)
{
exp.printStackTrace();
System.err.println("Exception "+exp.toString());
jLab0x28.setText(exp.getMessage());
continueMe = false;
}
}
public BufferedWriter getFile(String path)
{
try
{
File file = new File(path);
if (!file.exists())
{
file.createNewFile();
}
Here you are (1) testing for file existence and (2) creating a new file.
FileWriter fw = new FileWriter(file.getAbsoluteFile());
Here the operating system will create a new file regardless of what you did above. The exists()/createNewFile() part is therefore a complete waste of time: two system calls that accomplish precisely nothing. Remove them.
return new BufferedWriter(fw);
}
catch (IOException e)
{
e.printStackTrace();
}
return null;
Poor practice. You should let this method throw IOException and not catch it internally, or return null. At present, if this method fails, you will get an instrutable NullPointerException when you go to use its return value.
}
}

Android: DataOutputStream doesn't throw Exception

I have a server that accept more then one Client. Every Client is stored inside an ArrayList of Sockets. If a Client, for some reason, disconnects from my server, this should understand which client has been disconnected, close the client and delete it from the List.
Reading other question here I have understood that the only way to understand which client is disconnected is this: try to send data through all socket connected and the first one which throws Exception has to be closed.
The problem is that if the client is a simple Java-Application it works perfectly. But when the Client is an Android-Application, the data is sent through the (supposed) disconnected Socket. In this way my Server's algorithm doesn't throw Exceptions and it keeps sending data to all Sockets Causing a disaster. The code of clients (java and android) is Exactly the same but the results are different:
Server Code:
List<Socket> sList = new ArrayList<>();
Socket s;
int i = 0;
int whichSocket;
try
{
ServerSocket ss = new ServerSocket(7000);
while (true)
{
System.out.println("Server is Listening");
s = ss.accept();
sList.add(s);
System.out.println("Server Accepted Client --- " +s.toString());
Thread t2 = new Thread(new Runnable() {
public void run() {
try
{
DataInputStream dis = new DataInputStream(s.getInputStream());
while (true)
{
// For every message received from one client, it iterate through list sending that dat to ALL CLIENTS in the list of Socket
String test = dis.readUTF();
System.out.println("Message Sent By -- " + s.toString());
System.out.println(test);
while(i < sList.size()){
DataOutputStream dos = new DataOutputStream(sList.get(i).getOutputStream());
dos.writeUTF(test);
System.out.println("Messaggio Sent To -- " + sList.get(i).toString());
dos.flush();
++i;
}
i=0;
}
} catch (IOException e)
{
System.out.println("First Exception");
e.printStackTrace();
} finally
{
try
{
// An exception has been thrown. This means that one client is disconnected.Which One? Let's send data to all Clients in the list.
whichSocket = -1;
for(Socket temp : sList)
{
System.out.println("PENEEEE inviato a -- " + temp.toString());
whichSocket ++;
DataOutputStream dosser = new DataOutputStream(temp.getOutputStream());
dosser.write(1);
System.out.println("Message Sent To -- " + temp.toString());
dosser.flush();
}
}
catch (IOException e)
{
System.out.println("Second Exception");
e.printStackTrace();
}finally
{
try
{
sList.get(whichSocket).close();
System.out.println("Socket Closed --- " + sList.get(whichSocket).toString());
sList.remove(whichSocket);
} catch (IOException e) {
System.out.println("Third Exception");
e.printStackTrace();
}
}
}
}
});
t2.start();
}
} catch (IOException e) {
System.out.println("General Exception");
e.printStackTrace();
}
Client Code:
while(flag) {
if(!isConnected) {
try {
s = new Socket("192.168.1.69", 7000);
isConnected = true;
DataInputStream dis = new DataInputStream(s.getInputStream());
DataOutputStream dos = new DataOutputStream(s.getOutputStream());
while (flag) {
String result = dis.readUTF();
Log.d("InputStreammmm", result);
}
} catch (IOException e) {
Log.d("THIS IS", "THE EXCEPTIONN");
e.printStackTrace();
} finally {
isConnected = false;
}
}
}

Socket closed before able to read from ObjectInputStream(BufferedInputStream(Socket.getInputStream))

I have written a small Client/Server Program which already worked once but after adding Threads and some real input Data to it, i always get a closed Socket before being able to read the Object (the String). The Program always Prints "Client has already closed Connection!" from Function handleConnection in the ProcessDataThread.
ClientCode:
synchronized private static void sendToServer(){
Socket clientSocket = null;
BufferedOutputStream socketOut = null;
ObjectOutputStream out = null;
try{
String xmlToSend = "<startTag>\n<someOtherTag id=\"5555\">\n12345\n</someOtherTag>\n</startTag>\n";
Log.d(TAG, "Trying to send the following to the Server:" + xmlToSend);
//TODO load these from file
clientSocket = new Socket( "10.0.2.2", 7777);
socketOut = new BufferedOutputStream(clientSocket.getOutputStream());
out = new ObjectOutputStream(socketOut);
out.writeObject(xmlToSend);
out.flush();
}catch(Exception ex){
Log.e(TAG, "Could not write File to Server.", ex);
}
finally{
try{
if(clientSocket != null){
clientSocket.close();
}
if(out != null){
out.close();
}
}catch(IOException ex){
Log.e(TAG, "Could not close Socket.");
}
}
}
ServerCode:
ReceiverThread:
public void run()
{
try {
ServerSocket server = new ServerSocket(port);
//Only block for 10 Seconds and try again
server.setSoTimeout(10000);
while(!server.isClosed() && !stopped){
//Run
Socket client = null;
try
{
client = server.accept();
System.out.println("Accepted ClientConnection from " + client.getRemoteSocketAddress());
new ProcessDataThread(client).start();
}
catch( SocketTimeoutException tx){
//nothing
}
catch ( IOException e ) {
e.printStackTrace();
}
finally {
if ( client != null )
try { client.close(); } catch ( IOException e ) { e.printStackTrace(); }
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
ProcessDataThread:
public class ProcessDataThread extends Thread {
Socket client;
public ProcessDataThread(Socket sock) {
// xmlToProcess = xmlString;
this.client = sock;
}
private String handleConnection() {
BufferedInputStream socketIn = null;
ObjectInputStream in = null;
String xmlToProcess = null;
try {
if(!client.isClosed()){
System.out.println("Trying to read from Stream;");
socketIn = new BufferedInputStream(client.getInputStream());
in = new ObjectInputStream(socketIn);
Object xmlString = in.readObject();
System.out.println("Read some Object from Stream:" + xmlString.toString());
if (xmlString instanceof String) {
xmlToProcess = (String) xmlString;
System.out.println("Received the following XML:\n" + xmlToProcess);
}
}else{
System.out.println("Client has already closed Connection!");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (EOFException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (socketIn != null) {
socketIn.close();
}
if(client != null){
client.close();
}
} catch (IOException ioex) {
ioex.printStackTrace();
}
}
return xmlToProcess;
}
#Override
public void run() {
String xmlToProcess = handleConnection();
if (xmlToProcess == null || xmlToProcess.isEmpty()) {
// Es konnte kein String vom Client gelesen werden.
return;
}
System.out.println(xmlToProcess);
}
}
I made some changes with jboi's Suggestions. This is what i got now. The error stays the same. I don't even get to reading the Stream in the Server because client.getClosed()
is always true!
In the Client Code:
clientSocket = new Socket( "10.0.2.2", 7777);
clientSocket.setTcpNoDelay(true);
socketOut = new BufferedOutputStream(clientSocket.getOutputStream());
out = new ObjectOutputStream(socketOut);
out.writeObject(xmlToSend);
out.flush();
socketOut.flush();
//Close Output on Socket to signalize the Server that we finished writing!
clientSocket.shutdownOutput();
in = clientSocket.getInputStream();
byte[] receivedData = new byte[8192];
while(in.read(receivedData) != -1) {
//Wait for the Server to Close the Connection
}
In the Server Code
socketIn = new BufferedInputStream(client.getInputStream());
in = new ObjectInputStream(socketIn);
Object xmlString = in.readObject();
System.out.println("Read some Object from Stream:" + xmlString.toString());
if (xmlString instanceof String) {
xmlToProcess = (String) xmlString;
System.out.println("Received the following XML:\n" + xmlToProcess);
}
out = client.getOutputStream();
out.write(1);
//Signalize the Client that we have read everything
client.shutdownOutput();

It is very probable that your client has closed the socket in the finally block before the server was able to read the data.
In your clients finally block you should use socket.shutdownOutput, then read on the client all incoming data till EOF and then close the socket.
On your server you read till EOF and then send an object as kind of acknowledge, e.g. Number of bytes in the message. You also end the send with socket.shutdownOutput() as you've done at the client. This puts again an EOF at the end of the data. This EOF is received by the client and it will finally close the socket.

The issue seems to be the client and server are unable to identify each others state:
Client sending data to server, where server has closed the connection
Server sending/reading data to client , where client has closed the connection
Either are unable to coordinate with each other, solutions could be to establish a proper state machine. Some examples in Google if you search for (client and server state machine) gives mathematically definite state machine examples for your application: hope this comment helps.
Hence it's not useful to look into this problem in solution perspective and probably start using protocols in place like : telnet etc .

Ok now i'm feeling stupid.
I closed the Socket inside the Server Code myself.
After accepting a connection the following is executed inside the finally Block:
try {
client.close();
} catch (IOException e) {
e.printStackTrace();
}
The reason that there is this finally Block was because i didn't use Threads before so the ReceiverThread also did handle the Connection and therefore close the socket after using it.
I then moved the code to the new Thread and forgot to remove that finally block!

You can't use a buffered input stream and another kind of stream on the same socket. The buffered stream will steal data from the other one. Make up your mind. The ObjectInputStream will do everything you need. Just use that.
EDIT Re your edit, 'socket closed' means that you closed your socket and then continued to use it.

Exception with ObjectInputStream

I have three classes, the client, the server and the handler (which is going to handle the server connections) as I show below:
// The Client
public void sendSomePackage() {
try {
socket = new Socket("localhost", 54321);
sos = socket.getOutputStream();
oos = new ObjectOutputStream(sockOutput);
} catch (IOException e) {
e.printStackTrace(System.err);
return;
}
// About to start reading/writing to/from socket
try {
Package package = new Package(100);
oos.writeObject(pacote);
} catch (IOException e) {
e.printStackTrace(System.err);
}
try {
Thread.sleep(50);
} catch (Exception e) {
e.printStackTrace();
}
// Done reading/writing to/from socket, closing socket.
try {
sock.close();
} catch (IOException e) {
System.err.println("Exception closing socket.");
e.printStackTrace(System.err);
}
//Exiting
}
Now the server class:
// The Server - with a method that just wait for connections
public void waitForConnections() {
while (true) {
try {
socket = serverSocket.accept();
// Server:Accepted new socket, creating new handler for it
SimpleHandler handler = new SimpleHandler(socket);
handler.start();
// Server:Finished with socket, waiting for next connection
}
catch (IOException e){
e.printStackTrace(System.err);
}
}
}
My handler, which just handle the server connections:
#Override
public void run() {
//Handler: Handler run() starting
while (true) {
try {
package = (Package) ois.readObject();
if (pacote != null) {
System.out.println("Package received " + pacote.getSourceid());
}
} catch (Exception e) {
e.printStackTrace(System.err);
break;
}
}
try {
// SimpleHandler:Closing socket
sock.close();
ois.close();
} catch (Exception e) {
// Handler: Exception while closing socket, e=" + e);
e.printStackTrace(System.err);
}
}
The idea is the client send some 'package' object to my server which is going to keep running receiving the 'package' object any time.
The connection works fine, but in the end of the program an exception is launched, this is the one:
Package received 100
java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at br.ufscar.socket.SimpleHandler.run(SimpleHandler.java:45)
at java.lang.Thread.run(Unknown Source)
I already search for something on Google but nothing so far.
Any idea ?

This is working exactly as you want it to (probably). It reads the 100 then goes through the loop again (while(true) never stops looping until a break statement) and throws an exception because no more data has been sent and it goes to the catch statement and prints the error before exiting your while loop.

EOFException ist an IOException that indicates the end of an stream.

Here we say that if there aren't any more bytes to read then we should break out of the while loop before trying to read the object, etc.
while (true) {
if (ois.read() == -1) break;
//...rest of the code
}

Ok, this is how object streams work and the solution that works everywhere.
Object stream data is preceded by a 4 byte 'magical' sequence AC ED 00 05. An ObjectInputStream will peek for this data at construction time rather than before the first read. And that's logical: one wants to be sure it is a proper stream before being too far in an application. The sequence is buffered by the ObjectOutputStream at construction time so that it is pushed on the stream at the first write.
This method gives rise to complexities in buffered situations or transferring via sockets.
Fortunately there is a just as simple as effective solution to all these problems:
Flush the ObjectOutputStream immediately after construction!
ObjectOutputStream myStream = new ObjectOutputStream ( anotherStream );
myStream.flush();

ServerSocket java-server reads input only once?

I have written a java server and here is the code:
try
{
ss = new ServerSocket(8080);
while (true)
{
socket = ss.accept();
System.out.println("Acess given");
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
//out = new PrintWriter(socket.getOutputStream(),true);
line = in.readLine();
System.out.println("you input is :" + in.readLine());
}
}
And an iphone application is the client and there is the code for it:
- (void)viewDidLoad {
[super viewDidLoad];
socket = [[LXSocket alloc]init];
if ([socket connect:#"10.211.55.2" port:8080]) {
NSLog(#"socket has been created");
}
else {
NSLog(#"socket couldn't be created created");
}
#try {
}#catch (NSException * e) {
NSLog(#"Unable to send data");
}
[super viewDidLoad];
}
-(IBAction)sendData{
[socket sendString:#"A\n"];
}
I am having 2 problems here: first is that the server is only reading the input once. The second is that when ever I try to output the data it doesn't output until I have called the method twice (clicked on the uibutton twice). Not sure what is happening here. What am I doing wrong?

You are creating a new reader everytime in your while loop. Instead move the code outside the while loop and block on the readLine() call.
socket = ss.accept();
in = new BufferedReader(new InputStreamReader(socket.getInputStream());
String line = "";
while ( true) {
line = in.readLine();
System.out.println("you input is :" + line);
if ( "Bye".equals(line) )
break;
}
Here is an example server side program.

Since alphazero posted the pattern, I will post a brief stripped down implementation:
This is the Server:
try {
ServerSocket ss = new ServerSocket(portNumber);
logger.info("Server successfully started on port " + portNumber);
// infinite loop that waits for connections
while (true) {
SocketThread rst = new SocketThread(ss.accept());
rst.start();
}
} catch (IOException e) {
logger.info("Error: unable to bind to port " + portNumber);
System.exit(-1);
}
The SocketThread is something like:
public class SocketThread extends Thread {
private Socket communicationSocket = null;
public SocketThread(Socket clientSocket) {
communicationSocket = clientSocket;
try {
input = new ObjectInputStream(communicationSocket.getInputStream());
} catch (IOException e) {
logger.info("Error getting communication streams to transfer data.");
try {
communicationSocket.close();
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
public void run() {
boolean listening=true;
DataObject command = null;
while (listening) {
try {
Object currentObject = input.readObject();
if (currentObject != null
&& currentObject instanceof DataObject) {
command = (DataObject) currentObject;
}
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
// If we got to this point is because we received a request from
// the client
// we can exit the loop
listening = false;
}
}
}
}
Note: "DataObject" is just a custom class which could be more practical since you can read the Dataobject itself from the socket without worrying about how many bytes you are reading, etc. Only condition is that DataObject is flagged as Serializable.
Hope it helps.

Tushar,
The general pattern is this (almost java but pseudo-code):
while (server-socket is accepting new connections)
{
// The server-socket's job is to listen for connection requests
// It does this typically in a loop (until you issue server-shutdown)
// on accept the server-socket returns a Socket to the newly connected client
//
socket s = server-socket.accept-connection();
// various options here:
//
// typically fire off a dedicated thread to servie this client
// but also review NIO or (home-grown) connection-map/handler patterns
// the general pattern:
// create a dedicated thread per connection accepted.
// pass Socket (s) to the handler method (a Runnable) and start it off
// and that is it.
// Here we use the general pattern and create a dedicated
// handler thread and pass of the new connections' socket reference
//
Thread handler-thread = new Thread (handler-routine-as-runnable, s);
handler-thread.start();
}