09. User Logs

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class UserLogs {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        Map<String, LinkedHashMap<String, Integer>> usersWithIPsAndMessages = new TreeMap<>();
        String regex = "^IP=(?<IP>[0-9.A-Z:]+) message='(?<message>.*)' user=(?<user>.+){3,50}$";

        String input = scanner.nextLine();

        while (!"end".equals(input)) {
            Pattern pattern = Pattern.compile(regex);
            Matcher matcher = pattern.matcher(input);

            if (matcher.find()) {
                String IP = matcher.group("IP");
                int index = input.lastIndexOf("=");
                String user = input.substring(index + 1);

                if (!usersWithIPsAndMessages.containsKey(user)) {
                    usersWithIPsAndMessages.put(user, new LinkedHashMap<>());
                    usersWithIPsAndMessages.get(user).put(IP, 1);
                } else {
                    if (!usersWithIPsAndMessages.get(user).containsKey(IP)) {
                        usersWithIPsAndMessages.get(user).put(IP, 1);
                    } else {
                        usersWithIPsAndMessages.get(user).put(IP, usersWithIPsAndMessages.get(user).get(IP) + 1);
                    }
                }
            }

            input = scanner.nextLine();
        }

        if (!usersWithIPsAndMessages.isEmpty()) {
            usersWithIPsAndMessages.forEach((key, value) -> {
                System.out.printf("%s:%n", key);
                String result = convertWithStream(value) + ".";
                System.out.println(result);
            });
        }

    }

    public static String convertWithStream(Map<String, Integer> map) {
        return map.keySet().stream()
                .map(key -> key + " => " + map.get(key))
                .collect(Collectors.joining(", "));
    }
}