Versão utilizada no artigo de introdução ao profiler, com as otimizações finais

Main.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;
import java.util.regex.Pattern;

public class Main {

    private static final BufferedWriter WRITER = new BufferedWriter(new OutputStreamWriter(System.out));

    private static final Pattern PATTERN = 
        Pattern.compile("^(?=.{1,64}@)[A-Za-z0-9_-]+(\\.[A-Za-z0-9_-]+)*@[^-][A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*(\\.[A-Za-z]{2,})$");

    public static void main(String[] args) throws IOException {
        if (args.length != 1) {
            System.err.println("Deve-se passar o caminho do arquivo com os emails como parametro!");
            System.exit(1);
        }

        try (var fileReader = getFileReader(args[0])) {
            String line;
            while ((line = fileReader.readLine()) != null) {
                boolean isValidEmail = isValidEmail(line);

                printEmailLine(line, isValidEmail);
            }
        } catch (IOException e) {
            System.err.println("Erro enquanto inicializa o arquivo");
        } finally {
            WRITER.flush();
            WRITER.close();
        }
    }

    private static void printEmailLine(String line, boolean isValidEmail) throws IOException {
        if (isValidEmail) {
            WRITER.write("O email eh valido: " + line);
            WRITER.newLine();
        } else {
            WRITER.write("O email eh invalido: " + line);
            WRITER.newLine();
        }
    }

    private static boolean isValidEmail(String line) {
        return PATTERN
            .matcher(line)
            .matches();
    }

    public static BufferedReader getFileReader(String path) throws IOException {
        var file = new File(path);

        if (!file.exists() || !file.canRead() || file.isDirectory()) {
            System.err.println("Arquivo invalido: " + path);
            System.exit(1);
        }

        return new BufferedReader(new FileReader(file, StandardCharsets.UTF_16));
    }
}