如何在run方法之外发送对象？

Question

I want to be able to use my sendMessage() method to send something to my client while also waiting for client messages at the same time (the client should be able to do the same). I tried to define the Socket and Streamobjects everywhere but I think I don't really understand how they work.

    public class Server extends Thread{
private ObjectOutputStream oos;

public void sendMessage(String message){
    try
    {
        oos.writeObject(message);
    } catch (IOException e)
    {
        e.printStackTrace();
    }
}




public void run() {
    try {
        ServerSocket server = new ServerSocket(4444);
        Socket socket = server.accept();
        ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
        this.oos = oos;
        while(true) {
            ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
            String message = (String) ois.readObject();
            System.out.println("Server Received: " + message);
            ois.close();
            socket.close();
        }
    } catch (Exception e) {
    }
}


public class Main {

public static void main(String[] args)
{
   Server s =  new Server();
   s.start();
   new Client().start();
   s.sendMessage("test");

}

EDIT

Ok i tried to create a thread for each client but I still have the problem that I can't access the objectoutputstream...

public class SuperServer {
    private Server s = new Server();

    public void startServer(){
        s.setDaemon(true);
        s.start();

        if(s.isAlive()){
            System.out.println("server started");
        }
    }

    public void sendMessage(String message) throws IOException
    {
        s.handler.sendMessage(message);
    }
}

public class Server extends Thread {
    ServerSocket server;
    Socket socket;


    ServerHandler handler;



    public void run()
    {
        try {
            server = new ServerSocket(4444);


            while (true)
            {
                socket = server.accept();
                ServerHandler serverHandler = new ServerHandler(socket);
                handler = serverHandler;

            }
        } catch (IOException e)
        {
            e.printStackTrace();
        }
    }        
}

public class ServerHandler extends Thread {

    protected Socket socket;
    private ObjectOutputStream oos;
    private ObjectInputStream ois;

    public ServerHandler(Socket socket){
        this.socket = socket;
    }

    public void sendMessage(String message) throws IOException
    {
        oos.writeObject(message);
    }

    public void run()
    {
        try(
                ServerSocket server = new ServerSocket(4444);
                Socket socket = server.accept();
                ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
                ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
        )
        {
            this.socket = socket;
            this.oos = oos;
            while (true)
            {
                String message = (String) ois.readObject();
                System.out.println("Server Received: " + message);
            }
        } catch (IOException e)
        {
            e.printStackTrace();
        } catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }
    }


}

public class Main {



    public static void main(String[] args) throws IOException
    {
       SuperServer s = new SuperServer();
       s.startServer();

       SuperClient c = new SuperClient();
       c.clientStart();

       Scanner sc = new Scanner(System.in);
        System.out.println("input 1:");
        int a = Integer.parseInt(sc.nextLine());
        if(a == 1) s.sendMessage("test");


    }
}

Answer 1

You use incorrectly Thread and Socket.

1) In the server side, generally you want to create a new Thread for each new connection with a client to parallelize the communication between the server and its clients.
Here you create a Thread for the whole server processing...

2)That creates another issue because Threads.start() doesn't make run necessarily right now the thread. So here :

Server s =  new Server();
s.start();
new Client().start();
s.sendMessage("test");

The s.sendMessage("test"); may be invoked before Server and Client Threads are executed and terminated. So the ObjectOutputStream field could be still null .

3) You close the ServerSocket once a first message is read.
So even if s.sendMessage("test"); was invoked at the right time (by luck), ois will be not null but closed this time.

So in summarize :

• perform events at the correct time.
• create new Threads only when required. These are not details.
• don't close sockets if you want still to send/receive messages.