perlsufi perlsufi - 6 months ago 21
Java Question

Multithreading with client server program

I am trying to implement multi threading with a client/server program I have been working on. I need to allow multiple clients to connect to the server at the same time. I currently have 4 classes: a Client, a Server, a Protocol and a Worker to handle the threads. The following code is what I have for those classes:

SocketServer Class:

public class SocketServer {


public static void main(String[] args) throws IOException {

int portNumber = 9987;

try (
ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));

) {
Thread thread = new Thread(new ClientWorker(clientSocket));
thread.start(); //start thread

String inputLine, outputLine;

// Initiate conversation with client
Protocol prot = new Protocol();
outputLine = prot.processInput(null);
out.println(outputLine);

while ((inputLine = in.readLine()) != null) {
outputLine = prot.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("quit"))
break;
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
}


SocketClient Class:

public class SocketClient {
public static void main(String[] args) throws IOException
{

String hostName = "localhost";
int portNumber = 9987;

try (
Socket socket = new Socket(hostName, portNumber);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
) {
BufferedReader stdIn =
new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;

while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("quit"))
break;

fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
} catch (UnknownHostException e) {
System.err.println("Don't know about host " + hostName);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to " +
hostName);
System.exit(1);
}
}
}


Protocol Class:

public class Protocol {

private static final int waiting = 0;
private static final int sentPrompt = 1;


private int status = waiting;

public String processInput(String theInput) {
String theOutput = null;

if (status == waiting) {
theOutput = "Please enter what you would like to retrieve: 'customer' or 'product' ";
status = sentPrompt;
}
else if ( status == sentPrompt ) {
if ( theInput.equalsIgnoreCase("product")) {
File f = new File("product.txt");
Scanner sc = null;
try {
sc = new Scanner(f);
} catch (FileNotFoundException ex) {
Logger.getLogger(Protocol.class.getName()).log(Level.SEVERE, null, ex);
}

while ( sc.hasNextLine() ) {
String line = sc.nextLine();
theOutput = "The current product entries are : " + line;
}
return theOutput;
}
else if ( theInput.equalsIgnoreCase("customer")) {
File f = new File("customer.txt");
Scanner sc = null;
try {
sc = new Scanner(f);
} catch (FileNotFoundException ex) {
Logger.getLogger(Protocol.class.getName()).log(Level.SEVERE, null, ex);
}

while ( sc.hasNextLine() ) {
String line = sc.nextLine();
theOutput = "The current customer entries are : " + line;
}
return theOutput;

}
else if ( theInput.equalsIgnoreCase("quit")) {
return "quit";
}
else {
return "quit";
}
}
return theOutput;
}
}


The ClientWorker Class:

public class ClientWorker implements Runnable {
private final Socket client;

public ClientWorker( Socket client ) {
this.client = client;
}

@Override
public void run() {
String line;
BufferedReader in = null;
PrintWriter out = null;
try {
System.out.println("Thread started with name:"+Thread.currentThread().getName());
in = new BufferedReader(new InputStreamReader(client.getInputStream()));
out = new PrintWriter(client.getOutputStream(), true);
} catch (IOException e) {
System.out.println("in or out failed");
System.exit(-1);
}

while (true) {
try {
System.out.println("Thread running with name:"+Thread.currentThread().getName());
line = in.readLine();
//Send data back to client
out.println(line);
//Append data to text area
} catch (IOException e) {
System.out.println("Read failed");
System.exit(-1);
}
}
}
}


When I run the server and client, everything works fine as expected. Then when I try to run another client, it just hangs there and does not prompt the client to give a response. Any insight into what I am missing is greatly appreciated!

Answer

Your server code should address implement below functionalities.

  1. Keep accepting socket from ServerSocket in a while loop

  2. Create new thread after accept() call by passing client socket i.e Socket

  3. Do IO processing in client socket thread e.g ClientWorker in your case.

Have a look at this article

Your code should be

ServerSocket serverSocket = new ServerSocket(portNumber);
while(true){
  try{
    Socket clientSocket = serverSocket.accept();
    Thread thread = new ClientWorker(clientSocket);
    thread.start(); //start thread
  }catch(Exception err){
     err.printStackTrace();
  }
}
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