Многопоточность в Java. Часть 1

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("This program is running on: " + Thread.currentThread());
        System.out.println("Hello world");
    }
}

public class MyThread extends Thread {

    @Override
    public void run() {
        System.out.println("Executing code from: " + Thread.currentThread());
        System.out.println("Hello world");
    }
}

public class Playground {
    public static void main(String[] args) {
        System.out.println("Creating a new thread from : " + Thread.currentThread());
        var myThread = new MyThread();
        myThread.start();
        System.out.println("Leaving from: " + Thread.currentThread());
    }
}

public class MyRunnable implements Runnable {

    @Override
    public void run() {
        System.out.println("Using Runnable from: " +  Thread.currentThread());
        System.out.println("Hello world");
    }
}

public class Playground {
    public static void main(String[] args) {
        System.out.println("Creating a new thread from : " + Thread.currentThread());
        var myRunnable = new MyRunnable();
        var thread = new Thread(myRunnable);
        thread.start();
        System.out.println("Leaving from: " + Thread.currentThread());
   }
}

var thread = new Thread(new Runnable() {
    @Override
    public void run() {
        System.out.println("Using Runnable from: " + Thread.currentThread());
        System.out.println("Hello world");
    }
});
thread.start();

var thread = new Thread(() -> {
    System.out.println("Using Runnable from: " + Thread.currentThread());
    System.out.println("Hello world");
});
thread.start();

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.MalformedURLException;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.URL;
import java.util.stream.Collectors;

public class SingleThreadedServer {

    private final MostFrequentWordService mostFrequentWordService = new MostFrequentWordService();

    public SingleThreadedServer(int port) throws IOException {
        var serverSocket = new ServerSocket(port);
        while (true) {
            var socket = serverSocket.accept();
            handle(socket);
        }
    }

    public static void main(String[] args) throws IOException {
        new SingleThreadedServer(2222);
    }

    private void handle(Socket socket) {
        System.out.println("Client connected: " + socket);
        try (var in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
             var out = new PrintWriter(socket.getOutputStream(), true)) {
            out.println("Enter url:");
            String line;
            while ((line = in.readLine()) != null) {
                if (isValid(line)) {
                    var wordCount = mostFrequentWordService.mostFrequentWord(line)
                            .stream()
                            .map(counter -> counter.word() + ": " + counter.count())
                            .collect(Collectors.joining("\n"));
                    out.println(wordCount);
                } else if (line.contains("quit")) {
                    out.println("Goodbye!");
                    socket.close();
                } else {
                    out.println("Malformed URL");
                    out.println("Enter url:");
                }
            }
        } catch (IOException e) {
            System.out.println("Was unable to establish or communicate with client socket:" + e.getMessage());
        }
    }

    private static boolean isValid(String url) {
        try {
            new URL(url);
        } catch (MalformedURLException e) {
            System.out.println("invalid url: " + url);
            return false;
        }
        return true;
    }
}

import org.jsoup.Jsoup;

import java.io.IOException;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

record WordCount(String word, long count) {
}

public class MostFrequentWordService {

    public List<WordCount> mostFrequentWord(String url) throws IOException {
        var wordCount = Arrays.stream(getWords(url))
                .filter(value -> !value.isEmpty())
                .filter(value -> value.length() > 3)
                .map(String::toLowerCase)
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
        return wordCount.entrySet()
                .stream()
                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
                .limit(5)
                .map(entry -> new WordCount(entry.getKey(), entry.getValue()))
                .collect(Collectors.toList());
    }

    private String[] getWords(String url) throws IOException {
        var connect = Jsoup.connect(url);
        var document = connect.get();
        var content = document.body().text();
        return content.split("[^a-zA-Z]");
    }
}

public class MultiThreadedServer {
    private final MostFrequentWordService mostFrequentWordService = new MostFrequentWordService();

    public MultiThreadedServer(int port) throws IOException {
        var serverSocket = new ServerSocket(port);
        while (true) {
            var socket = serverSocket.accept();
            var thread = new Thread(() -> handle(socket));
            thread.start();
        }
    }
    
    // оставшийся код будет без изменений
}