CODEWITHSUNDEEP
javasocketsconcurrencyclientserver
Jonny
Jonny

Reputation: 67

Java Socketing: My server class constantly takes in input but my client doesn't?

Try to do some concurrent messaging between the server and the client. When they first connect to eachother and the Server sends the test string, the client gets it perfectly fine the first time. And the client can SEND messages just fine to the Server. But my Client class cant constantly check for messages like my Server can and idk what's wrong. Any suggestions?

Server class code:

import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.Random;
import java.util.concurrent.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Server {

String testMessage = "You are now connected and can begin chatting!";
boolean connected = false;
int port;


public Server(int port) {
    this.port = port;
}

public void Open() {

    //creates Threadpool for multiple instances of chatting
    final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
    Runnable serverTask = new Runnable() {

        @Override
        public void run() {
            try {
                System.out.println("Opening...");

                ServerSocket srvr = new ServerSocket(port);
                while (true) {
                    Socket skt = srvr.accept();
                    clientProcessingPool.submit(new ClientTask(skt));
                }
            } catch (Exception e) {
                try {
                    System.out.println(e);
                    System.out.print("You're opening too many servers in the same location, fool!\n");
                    ServerSocket srvr = new ServerSocket(port);
                    while (true) {
                        Socket skt = srvr.accept();
                        clientProcessingPool.submit(new ClientTask(skt));
                    }
                } catch (IOException ex) {
                    Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
    };
    Thread serverThread = new Thread(serverTask);
    serverThread.start();
}

private class ClientTask implements Runnable {

    private final Socket skt;

    private ClientTask(Socket skt) {
        this.skt = skt;
    }

    @Override
    public void run() {
        //for sending messages
        if (connected == false) {
            System.out.println("======================");
            System.out.println("Server has connected!");
            processMessage(testMessage);
        }
        //for receiving messages
        while (true) {
            try {
                // Read one line and output it
                BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
                String incomingMessage = br.readLine();
                if (incomingMessage != null) {
                    System.out.println("Server: Received message: " + incomingMessage);
                    processMessage(incomingMessage);
                }
                //br.close();
                //skt.close(); //maybe delete
            } catch (Exception e) {
                System.out.println("Server had error receiving message.");
                System.out.println("Error: " + e);
            }
        }
    }

    //for processing a message once it is received
    public void processMessage(String message) {
        PrintWriter out = null;
        try {
            out = new PrintWriter(skt.getOutputStream(), true);
        } catch (IOException ex) {
            System.out.println(ex);
            System.out.println("Server had error sending message.");
        }
        System.out.print("Server: Sending message: " + message + "\n");
        out.print(message);
        out.flush();
        connected = true;
        try {
            skt.shutdownOutput();
            //out.close();
        } catch (IOException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}
}

Client class code:

import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JOptionPane;

class Client {

public String message;
Socket skt;
public int port;

public Client(int port) {
    this.port = port;
}

//for receiving messages from Server
public void receiveMessage() {
    final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
    Runnable serverTask = new Runnable() {
        @Override
        public void run() {
            try {
                skt = new Socket(InetAddress.getLocalHost().getHostName(), port);
                while (true) {

                    clientProcessingPool.submit(new Client.ClientTask(skt));
                }
            } catch (IOException ex) {
                Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
            }

        }
    };
    Thread serverThread = new Thread(serverTask);
    serverThread.start();
}

//for sending messages to Server
public void sendMessage(String outgoingMessage) throws IOException {
    try {
        skt = new Socket(InetAddress.getLocalHost().getHostName(), port);
        PrintWriter pw = new PrintWriter(skt.getOutputStream());
        System.out.println("Client: Sending message: " + outgoingMessage);
        pw.print(outgoingMessage);
        pw.flush();
        skt.shutdownOutput();
        //skt.close(); //maybe delete
    } catch (Exception e) {
        System.out.println(e);
        System.out.print("Client had error sending message.\n");
        JOptionPane.showMessageDialog(null, "That User is not currently online.", "ERROR!!", JOptionPane.INFORMATION_MESSAGE);
    }

}

private class ClientTask implements Runnable {

    private final Socket skt;

    private ClientTask(Socket skt) {
        this.skt = skt;
    }

    @Override
    public void run() {
        while (true) {
            try {
                BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));
                //while (!in.ready()) {}
                String incomingMessage = in.readLine();
                if (incomingMessage != null) {
                    System.out.println("Client: Received message: " + incomingMessage); // Read one line and output it
                    message = incomingMessage;
                }
                //skt.shutdownInput();
                //in.close();
                //skt.close(); //maybe delete
            } catch (Exception e) {
                System.out.print("Client had error receiving message.\n");
            }
        }
    }
}
}

Upvotes: 0

Views: 760

Answers (1)

Vince
Vince

Reputation: 15146

Streams cannot be re-wrapped. Once assigned to a wrapper, they must use that wrapper for the entire life-cycle of the stream. You also shouldn't close a stream until you are done using it, which in this case isn't until your client and server are done communicating.

In your current code, there are a few times where you re-initialize streams:

while (true) {
    try {
        //Each loop, this reader will attempt to re-wrap the input stream
        BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));

        String incomingMessage = br.readLine();
        if (incomingMessage != null) {
            System.out.println("Server: Received message: " + incomingMessage);
            processMessage(incomingMessage);
        }

        //don't close your stream and socket so early!
        br.close();
        skt.close();
    } catch (Exception e) {
        //...
    }

You get the idea; you can use this knowledge to find the stream problems in your client code as well.

With that said, servers are the middle-man between multiple clients. If you want to be able to type in the server's console to send a message to clients, it shouldn't go to only 1 client (unless you had a system that allowed you to specify a name). You need to store every connection in some kind of collection so when you type in the server's console, it goes to every client that's connected. This also helps when a client wants to send a message to every other client (global message). The server's main thread is primarily for accepting clients; I created another thread to allow you to type in the console.

As for your streams, you should create them whenever you start the ClientTask, both server side and client side:

public class Server {
    private ExecutorService executor = Executors.newFixedThreadPool(10);
    private Set<User> users = new HashSet<>();

    private boolean running;
    private int port;

    public Server(int port) {
        this.port = port;
    }

    public void start() {
        running = true;

        Runnable acceptor = () -> {
            try(ServerSocket ss = new ServerSocket(port)) {
                while(running) {
                     User client = new User(ss.accept());
                     users.add(client);
                     executor.execute(client);
                }
            } catch(IOException e) {
                //if a server is already running on this port;
                //if the port is not open;
                e.printStackTrace();
            }
        };

        Runnable userInputReader = () -> {
            try(Scanner scanner = new Scanner(System.in)) {
                while(running) {
                    String input = scanner.nextLine();

                    for(User user : users) {
                        user.send(input);
                    }
                }
            } catch(IOException e) {
                //problem sending data;
                e.printStackTrace();
            }

        };

        Thread acceptorThread = new Thread(acceptor);
        Thread userThread = new Thread(userInputReader);
        acceptorThread.start();
        userThread.start();
    }

    public void stop() {
        running = false;
    }

    public static void main(String[] args) {
        new Server(15180).start();
        System.out.println("Server started!");
    }
}

In the run() method is where the streams should be wrapped.

class User implements Runnable {
    private Socket socket;
    private boolean connected;

    private DataOutputStream out; //so we can access from the #send(String) method

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

    public void run() {
        connected = true;

        try(DataInputStream in = new DataInputStream(socket.getInputStream())) {
            out = new DataOutputStream(socket.getOutputStream());

             while(connected) {
                 String data = in.readUTF();
                 System.out.println("From client: "+data);
                 //send to all clients
             }
         } catch(IOException e) {
             //if there's a problem initializing streams;
             //if socket closes while attempting to read from it;
             e.printStackTrace();
         }
    }

    public void send(String message) throws IOException {
        if(connected) {
            out.writeUTF(message);
            out.flush();
        }
    }
}

It's pretty much the same idea with the client: 1. Connect to Server 2. Create "communication" thread 3. Create "user input" thread (to receive input from console) 4. Start threads

public class Client {
    private final String host;
    private final int port;

    private boolean connected;
    private Socket socket;

    public Client(String host, int port) {
        this.host = host;
        this.port = port;
    }

    public void start() throws IOException {
        connected = true;
        socket = new Socket(host, port);

        Runnable serverInputReader = () -> {
            try (DataInputStream in = new DataInputStream(socket.getInputStream())) {
                while (connected) {
                    String data = in.readUTF();
                    System.out.println(data);
                }
            } catch (IOException e) {
                // problem connecting to server; problem wrapping stream; problem receiving data from server;
                e.printStackTrace();
            }
        };

        Runnable userInputReader = () -> {
            try (DataOutputStream out = new DataOutputStream(socket.getOutputStream());
                    Scanner scanner = new Scanner(System.in)) {
                while (connected) {
                    String input = scanner.nextLine();
                    out.writeUTF(input);
                }
            } catch (IOException e) {
                //problem wrapping stream; problem sending data;
                e.printStackTrace();
            }
        };

        Thread communicateThread = new Thread(serverInputReader);
        Thread userThread = new Thread(userInputReader);
        communicateThread.start();
        userThread.start();
    }

    public static void main(String[] args) throws IOException {
        new Client("localhost", 15180).start();
    }
}

There are a few things I used in the code above that you may not be familiar with. They help simplify the syntax for your code:

  • Lambda Expressions - Prevents the need to create an anonymous class (or subclass) to declare a method
  • Try-With-Resources - Closes the resources specified automatically once the try block as ended

EDIT When a user connects, you should store their connection by name or id. That way, you can send data to specific users. Even if your client is running on the same machine as the server, it's still the same idea: client connects to server, server sends message to client based on name or id:

            while(running) {
                 User client = new User(ss.accept());
                 users.add(client); //add to set
                 executor.execute(client);
            }

Right now, you are simply adding users to a Set. There is currently no way to grab a specific value from this set. What you need to do is give it some kind of "key". To give you an idea, here's an old algorithm I used to use. I have an array full of empty slots. When someone connects, I look for the first empty slot. Once an empty slot is found, I pass the user the index of the array it's being stored at (that will be the user's id), then store the user in the array at the specified index. When you need to send a message to someone, you can use the id to access that specific array index, grab the user you want and send a message:

class Server {
    private int maxConnections = 10;
    private ExecutorService executor = Executors.newFixedThreadPool(maxConnections);
    private User[] users = new User[maxConnections];

    //...

    while(running) {
        Socket socket = ss.accept();

        for(int i = 0; i < users.length; i++) {
            if(users[i] == null) {
                users[i] = new User(socket, i);
                executor.execute(users[i]);
                break;
            }
        }
    }

    //...

    public static void sendGlobalMessage(String message) throws IOException {
        for(User user : users)
            if(user != null)
                user.send(message);
    }

    public static void sendPrivateMessage(String message, int id) {
        User user = users[id];

        if(user != null) {
            user.send(message);
        }
    }
}

class User {
    private Socket socket;
    private int id;

    private DataOutputStream out;

    public User(Socket socket, int id) {
        this.socket = socket;
        this.id = id;
    }

    public void send(String message) throws IOException {
        out.writeUTF(message);
        out.flush();
    }

    public void run() {
        DataInputStream in;
        //wrap in and out streams

        while(connected) {
            String data = in.readUTF();

            //Server.sendGlobalMessage(data);
            //Server.sendPrivateMessage(data, ...);
            sendMessage(data); //sends message back to client
        }
    }
}

Upvotes: 1

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