CodeGym/Help with Java Tasks/2 conditions doesn't validate

Level 41

Provins

10.09.2019
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2 conditions doesn't validate

Question about the task

Chat (part 14)

Java Multithreading, Level 6, Lesson 15

Resolved

It seems easy in the condition so I don't really understand where is the problem :(

Let's start writing the main functionality of the Client class.

1) Add a public void run() method. It should create a helper SocketThread, wait until it establishes a connection with the server, and then in a loop, read messages from the console and send them to the server. The loop will terminate either when the client shuts down or the user enters the 'exit' command'.
To inform the main thread that the connection is established on the helper thread, use the Client object's wait() and notify() methods.

The implementation should:
a) Create a new socket thread using the getSocketThread() method.
b) Mark the created thread as a daemon. This is necessary so that the helper thread is automatically interrupted when the program exits.
c) Start the helper thread.
d) Make the current thread wait until it receives a notification from another thread.
Hint: use wait() and object level synchronization. If an exception occurs while waiting, notify the user and exit the program.
d) Once the thread receives a notification, check the value of clientConnected. If it is true, display "Connection established. To exit, enter 'exit'.". If it is false, display "An error occurred while working with the client.".
e) Read messages from the console until the client is connected. If 'exit' is entered, then exit the loop.
g) After each string is read, if the shouldSendTextFromConsole() method returns true, send the text using the sendTextMessage() method.

2) Add the public static void main(String[] args) method. It must create a new Client object and call its run() method.

Requirements:

The main() method should create a new Client object and call its run() method.
The run() method should create and start a new thread that is obtained using the getSocketThread() method.
The thread created using the getSocketThread() method should be marked as a daemon (setDaemon(true)).
After starting the new socketThread, the run() method should wait until it is awakened.
As long as the clientConnected flag is true, messages should be read from the console using the ConsoleHelper.readString() method.
If the "exit" command is entered, you should interrupt the message-reading loop.
If the shouldSentTextFromConsole() method returns true, the sendTextMessage() method should be called with the input text used as an argument.

package com.codegym.task.task30.task3008; import java.net.*; import java.util.*; import java.util.concurrent.ConcurrentHashMap; import java.io.IOException; public class Server { private static Map<String, Connection> connectionMap = new ConcurrentHashMap<String, Connection>(); public static void sendBroadcastMessage(Message message) { Iterator<Connection> valueIterator=connectionMap.values().iterator(); while(valueIterator.hasNext()){ try{ valueIterator.next().send(message); } catch (IOException e){ System.out.println("Message couldn't be sent"); } } } public static void main (String[] args){ int port = ConsoleHelper.readInt(); ServerSocket serverSocket = null; try{ serverSocket= new ServerSocket(port); System.out.println("Server is running"); while (true){ Socket s = serverSocket.accept(); Thread thread = new Handler(s); thread.start(); } } catch (Exception e){ System.out.println(e.getMessage()); try{ serverSocket.close(); }catch (Exception ex){ ex.printStackTrace(); } } } private static class Handler extends Thread{ private Socket socket; public Handler (Socket socket){ this.socket = socket; } private String serverHandshake(Connection connection) throws IOException, ClassNotFoundException { boolean nameRequestOk = true; boolean isAlreadyTaken = false; Message response = null; boolean isKeyPresent = false; while (nameRequestOk) { connection.send(new Message(MessageType.NAME_REQUEST)); response = connection.receive(); if (response.getType().equals(MessageType.USER_NAME)){ if (!response.getData().equals("")){ isKeyPresent = connectionMap.containsKey(response.getData()); if (!isKeyPresent){ connectionMap.put(response.getData(), connection); connection.send(new Message(MessageType.NAME_ACCEPTED)); nameRequestOk = false; } } } } return response.getData(); } private void notifyUsers(Connection connection, String userName) throws IOException { String name = userName; for (Map.Entry<String, Connection> entry : connectionMap.entrySet()){ if( entry.getKey() != userName) { connection.send(new Message(MessageType.USER_ADDED, entry.getKey())); } } } private void serverMainLoop(Connection connection, String userName) throws IOException, ClassNotFoundException { while (true) { try { Message received = connection.receive(); if (received.getType().equals(MessageType.TEXT)) { String m = userName + ": " + received.getData(); sendBroadcastMessage(new Message(MessageType.TEXT, m)); } else { String error = "not text error"; ConsoleHelper.writeMessage(error); } } catch (Exception e) { ConsoleHelper.writeMessage(e.getMessage()); } } } @Override public void run(){ ConsoleHelper.writeMessage("New connection using " +socket.getRemoteSocketAddress()+" is established."); String newClient=""; Connection connection=null; try { connection = new Connection(socket); newClient = serverHandshake(connection); sendBroadcastMessage(new Message(MessageType.USER_ADDED, newClient)); notifyUsers(connection, newClient); serverMainLoop(connection, newClient); connectionMap.remove(newClient); sendBroadcastMessage(new Message(MessageType.USER_REMOVED, newClient)); connection.close(); }catch (IOException i){ if(newClient != ""){ connectionMap.remove(newClient); sendBroadcastMessage(new Message(MessageType.USER_REMOVED, newClient)); try{ connection.close(); }catch (IOException y){ } } }catch (ClassNotFoundException c){ if(newClient != ""){ connectionMap.remove(newClient); sendBroadcastMessage(new Message(MessageType.USER_REMOVED, newClient)); try{ connection.close(); }catch (IOException y){ } } }catch (Exception e){ if(newClient != ""){ connectionMap.remove(newClient); sendBroadcastMessage(new Message(MessageType.USER_REMOVED, newClient)); try{ connection.close(); }catch (IOException y){ } } } } } }

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Roman

Level 41

11 September 2019, 08:50

solution

In the Client class: - don't use notify(); - don't use System.exit(0); - hint from Intellij IDEA: variable "isClientConnected" is not updated inside loop

Nicolas Huet

Level 41 , Provins, France

11 September 2019, 08:55

thank you i'll work on that. but you say that I should not use notify() but why is it written in the conditions :

To inform the main thread that the connection is established on the helper thread, use the Client object's wait() and notify() methods.

Nicolas Huet

Level 41 , Provins, France

11 September 2019, 09:37

I tried this for the moment but I'm not sur if heading in the right direction with this (I still used notify() because the conditions says to use it but i'll try with something else too)

public void run(){
        SocketThread socketThread = getSocketThread();
        socketThread.setDaemon(true);
        socketThread.start();

        try {

        synchronized (this) {
            wait();
            }
            notify();
            }catch (InterruptedException i) {
                ConsoleHelper.writeMessage("An error occurred during the wait of main method. Exiting the program.");
                return;
        }

        if ((clientConnected = socketThread.isAlive())){
            ConsoleHelper.writeMessage("Connection established. To exit, enter 'exit'.");
            while ((clientConnected = socketThread.isAlive())){
            String s = ConsoleHelper.readString();
            if (s.equals("exit")){
                break;
            }
            if (shouldSendTextFromConsole()) {
                sendTextMessage(s);
            }

        }
        }
        else {
            ConsoleHelper.writeMessage("An error occurred while working with the client.");
        }

    }

Nicolas Huet

Level 41 , Provins, France

11 September 2019, 17:17

I have tried a bunch of other ways.... I have no clues about what to do now... I completely don't see how doing it without notify, I can't see another way than that follow to update the clientConnected boolean, I don't really see how to not use System.exit(0), the only I found was with return but I'm sur it will not work like that. I tried to put all the logique after the notify it didn't help etc. I must be blind but I'm really really stuck here..

public void run(){
        SocketThread socketThread = getSocketThread();
        socketThread.setDaemon(true);
        socketThread.start();

        try {
        synchronized (this) {
            wait();
            if ((clientConnected = socketThread.isAlive())) {
                notify();
            }
        }
            }catch (InterruptedException i) {
                ConsoleHelper.writeMessage("An error occurred during the wait of main method. Exiting the program.");
                return;
        }

        if ((clientConnected = socketThread.isAlive())){
            ConsoleHelper.writeMessage("Connection established. To exit, enter 'exit'.");
            while ((clientConnected = socketThread.isAlive())){
                String s = ConsoleHelper.readString();
                if (s.equals("exit")){
                    break;
                }
                if (shouldSendTextFromConsole()) {
                    sendTextMessage(s);
                }
            }
        }
        else {
            ConsoleHelper.writeMessage("An error occurred while working with the client.");
        }


    }

Roman

Level 41

12 September 2019, 05:54

"- hint from Intellij IDEA: variable "isClientConnected" is not updated inside loop" I mean :

boolean isClientConnected = clientConnected;

Use clientConnected instead of isClientConnected

Nicolas Huet

Level 41 , Provins, France

12 September 2019, 07:55

Your solution to the task was better than 0% other students. You solved it in 114 attempts. The average number of attempts for this task is 12.52. This task has been completed by 21 students.

finally!.... Thank you! Perhaps the mention to the usage of "notify" should be removed from the conditions tasks since it clearly show a wrong path to follow.

jorge ives murillo paredes

Level 40 , New York City, United States

15 April 2020, 16:09

hi ,I been struggleling whit the same problem,can you help me?

jorge ives murillo paredes

Level 40 , New York City, United States

24 April 2020, 01:13

Hi romam ,im stuck in this task can you help me.