new thread is created, but doesn't run (java)

Question

here's a little code I wrote. This next class waits for a connection and creates a new thread upon receiving one:

    ServerSocket serverSocket = null;
    ExecutorService serv = Executors.newCachedThreadPool();
    serv.execute(new UserThread());
    try {
        serverSocket = new ServerSocket(FMDataManager.getPort());
        serverSocket.setSoTimeout(0);
        while (_listening){
            System.out.println("Listening on port "+FMDataManager.getPort());
            System.out.println("Waiting for connections.");
            serv.execute(new UploadThread(serverSocket.accept()));          
        }
    } catch (IOException e) {
        System.err.println("Could not listen on port: "+FMDataManager.getPort()+".");
        System.exit(-1);
    }

as you can see i am using ServerSocket.accept() method to wait for a connection. The thread is indeed created, but it won't run. I put a little "thread created" in its constructor and another message "starting thread" in run(), but I only got the first message. After that it didn't do anything, I didn't even get "thread created". Any ideas please?

I've add the implementation of the UploadThread I am trying to start, maybe It'll help

public class UploadThread extends Thread{

Socket _socket;

public UploadThread(Socket socket) {
    super("UserThread");
    _socket = socket;
}
public void run(Socket socket) {
    System.out.println("entred upload thread");
    DataOutputStream out = null;
    DataInputStream in = null;
    try {
        out = new DataOutputStream(_socket.getOutputStream());
        in = new DataInputStream(_socket.getInputStream());
        FileMessage inputMessage;
        SendFile outputMessage;
        inputMessage = (FileMessage) CommandEnum.readMessage(in);
        System.out.println("F: "+inputMessage.getCaption());
        File file = null;
        Iterator<File> itr = FMDataManager.getFiles().iterator();
        while (itr.hasNext()){
            File temp = itr.next();
            if (temp.getName().equals(inputMessage.getFile()))
                file = temp;
        }
        outputMessage = new SendFile(file);
        outputMessage.send(out);
    } catch (IOException e) {
        e.printStackTrace();
    } finally{
        try {
            _socket.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}
}

Answer 1

Try serv.submit instead of serv.execute .

EDIT

Looks like UploadThread isn't overriding run() correctly. That being said, your run method declaration should look like this:

@Override
public void run(){
    //do stuff
}

There's no need to pass socket as an argument.

Answer 2

As indicated by sthupahsmaht's comment your UploadThread implementation is wrong. The signature for the run() method is public void run() . Currently you are creating a new method with the signature public void run(Socket) . As run() doesn't take any arguments you have to pass all parameters via the constructor or setters.

There are two best practices that can help you avoid such mistakes in the future:

• Whenever you implement or override a method, annotate it with @Override . If you create a new method with @Override , the compiler signals an error.
• Don't extend Thread but implement Runnable . Thread has a default implementation for run() which does nothing. This is what happens with your code currently.

Answer 3

Without seeing the part of the code that actually constructs the thread, I'll guess you're NOT calling the 'start()' method on the thread object.

Needs to be something like this:

Thread thr = new Thread(new Runnable() { void run() { /* do stuff */ }) ;

thr.start() // GO!