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Chat (part 10)

Java Multithreading, Level 6, Lesson 15

Under discussion

I don't see the error. I think I have tried everything.

The third stage is the server's main message-processing loop.
Add a private void serverMainLoop(Connection connection, String userName) throws IOException, ClassNotFoundException
method, where the meaning of the parameters is the same as in the notifyUsers() method.

It must:
1) Receive client messages
2) If a received message is text (TEXT), then generate a new text message by concatenating the client name,
a colon, a space, and the text message. For example, if we received a message with the text
"Hi, everyone" from the user "Bob", then you would need to generate this message: "Bob: Hi, everyone".
3) Send the generated message to all clients using the sendBroadcastMessage() method.
4) If the received message is not text, display an error message
5) Create an infinite loop and move the functionality of steps 10.1-10.4 into the loop.

Requirements:

The Handler class should have a private void serverMainLoop(Connection connection, String userName) method.
The serverMainLoop method should receive messages from the client in an infinite loop (use the Connection class's receive method).
If the message received by the serverMainLoop method is a MessageType.TEXT, then a new message should be sent to all chat participants using the sendBroadcastMessage method (the formatting of the message is described in the task conditions).
If the message received by the serverMainLoop method is some type other than MessageType.TEXT, the sendBroadcastMessage method should not be called and an error message should be displayed.

package com.codegym.task.task30.task3008; import java.io.IOException; import java.net.ServerSocket; import java.net.Socket; import java.util.Iterator; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; public class Server { private static Map<String, Connection> connectionMap = new ConcurrentHashMap<>(); public static void main(String[] args) throws IOException { int port = ConsoleHelper.readInt(); ServerSocket serverSocket = null; try { serverSocket = new ServerSocket(port); System.out.println("The server is running."); while(true) { Socket socket = serverSocket.accept(); (new Handler(socket)).start(); } } catch(IOException e) { System.out.println("Error in data input/output."); serverSocket.close(); } } private static class Handler extends Thread { private Socket socket; public Handler(Socket socket) { this.socket = socket; } private String serverHandshake(Connection connection) throws IOException, ClassNotFoundException { while (true) { connection.send(new Message(MessageType.NAME_REQUEST)); Message request = connection.receive(); if (request.getType() != MessageType.USER_NAME || request.getData().isEmpty() || connectionMap.containsKey(request.getData())) { continue; } connectionMap.put(request.getData(), connection); connection.send(new Message(MessageType.NAME_ACCEPTED)); return request.getData(); } } public static void sendBroadcastMessage(Message message) { try { for (Map.Entry<String, Connection> pair : connectionMap.entrySet()) { pair.getValue().send(message); } } catch (IOException e) { System.out.println("The message could not be send."); } } private void notifyUsers(Connection connection, String userName) throws IOException { for(Map.Entry<String, Connection> pair : connectionMap.entrySet()) { if(!pair.getKey().equals(userName)) { connection.send(new Message(MessageType.USER_ADDED, pair.getKey())); } } } private void serverMainLoop(Connection connection, String userName) throws IOException, ClassNotFoundException { while(true) { Message message = connection.receive(); if (message.getType() == MessageType.TEXT) { String text = String.format("%s: %s", userName, message.getData()); sendBroadcastMessage(new Message(MessageType.TEXT, text)); } else { ConsoleHelper.writeMessage("Error, No text message received."); } } } } }

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Thomas

Level 41 , Bayreuth, Germany

1 April, 07:13

Looking over your code I didn't see any bigger problems (however if you implement Serializable you always should add a SerialVersionUID). So I suggest to take care of previous tasks requirements and replace all occurrences of System.out.println with the ConsoleHelper variant (if I'm not wrong that's three times the case).

FelixUjo

Level 35 , Gijón, Spain

1 April, 20:19

I replaced the System.out.println with ConsoleHelper.writeMessage() and added a serialVersionUID, something I was unaware of, but it is still not valid.

Thomas

Level 41 , Bayreuth, Germany

2 April, 16:35

The serialVersioniUID isn't critical just good practice. After looking a little bit closer I suggest to check your main method. You don't close the ServerSocket object. Just if there is an exception. Try using two try blocks. One to create the server socket and the second handling the loop. Here have a finally block that closes the server socket.

} finally {
    if (socket != null)
        socket.close();
}

PS: I do not see any problem with the code for this part. So if that is not the problem you should recheck all previous steps. I also had some validation problems with this task but I do not remember exactly anymore what it was.

FelixUjo

Level 35 , Gijón, Spain

2 April, 19:41

I don't see it. It's frustrating. Thank you.

Thomas

Level 41 , Bayreuth, Germany

2 April, 20:04

I'm not sure if I understand what you don't see? That the ServerSocket isn't closed? There is only one serverSocket.close() in your code and that's inside a catch block. So just in case an exception is thrown you try to close the socket. Usually you either use a) (preferrably) a try-with-resources b) a finally block. Here you usually want to make sure the object really exists before trying to close it (test for null). Otherwise there may be NullPointerException in your finally block that you need to take care of, too. And yes, these big tasks may be frustration at times. I had not just one task that I started from scratch because there was some problem I wasn't able to find and I was sure I had introduced it some parts before.

FelixUjo

Level 35 , Gijón, Spain

2 April, 20:23

I did that and it is still not valid, I give up.