email-extractor.java

package ua.samosfator;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) throws Exception {
        final List<String> lines = new ArrayList<>();
        String result = "";
        Files.walk(Paths.get("")).forEach(filePath -> {
            if (Files.isRegularFile(filePath)) {
                String[] fileNameParts = filePath.toString().split("\\.");
                String fileExtension = fileNameParts[fileNameParts.length - 1];
                if (fileExtension.equals("txt")) {
                    try {
                        List<String> fileLines = Files.readAllLines(filePath);

                        fileLines = fileLines.stream()
                                .filter(line -> line.contains("From: ") || line.contains("E-mail"))
                                .collect(Collectors.toList());

                        lines.addAll(fileLines);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        });

        for (String line : lines) {
            String[] parts = line.split(": "); // "From", "[email protected]"

            parts[0] = parts[0].trim();
            parts[1] = parts[1].trim();

            if (parts[0].contains("From")) {
                if (!parts[1].contains("main-hosting.eu")) {
                    result += parts[1] + ":";
                }
            }

            if (parts[0].contains("E-mail")) {
                if (parts[0].length() < 10) {
                    result += parts[1] + ":";
                } else {
                    result += parts[1] + System.lineSeparator();
                }
            }
        }

        PrintWriter printWriter = new PrintWriter(new File("output.txt"));
        printWriter.println(result);
        printWriter.flush();
        printWriter.close();
        System.out.println(result);
    }
}