Cipher / Decipher

Cipher.java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Cipher {


    static Map<String, Integer> numericCipherAssignments = new HashMap<>() {
        {
            put("A", 0);
            put("B", 1);
            put("C", 2);
            put("D", 3);
            put("E", 4);
            put("F", 5);
            put("G", 6);
            put("H", 7);
            put("I", 8);
            put("J", 9);
            put("K", 10);
            put("L", 11);
            put("M", 12);
            put("N", 13);
            put("O", 14);
            put("P", 15);
            put("Q", 16);
            put("R", 17);
            put("S", 18);
            put("T", 19);
            put("U", 20);
            put("V", 21);
            put("W", 22);
            put("X", 23);
            put("Y", 24);
            put("Z", 25);
        }
    };

    private static Map<Integer, String> cipherReversedAssignments;

    public static void main(String[] args) throws IOException {

        cipherReversedAssignments = numericCipherAssignments.entrySet()
                .stream()
                .collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));

        String keyFilePath = "src/key.txt";
        List<Integer> encodedKeyParts = readAndEncodeFile(keyFilePath);
        // Deciphering for exercise 2
        decodeMessageWithKey(encodedKeyParts);
        //Ciphering for exercise 3
        encodeMessageWithKey("OPERACION OVERLORD DIEZ JULIO CALAIS", encodedKeyParts);
    }

    private static void encodeMessageWithKey(String message, List<Integer> encodedKeyFragments) {
        List<Integer> messageEncoded = Arrays.stream(message.replaceAll("\\s+", "").split(""))
                .map(numericCipherAssignments::get).collect(Collectors.toList());

        StringBuilder cipheredMessage = new StringBuilder();
        for (int i = 0; i < messageEncoded.size() ; i++) {
            int messagePart = messageEncoded.get(i);
            int keyPart = encodedKeyFragments.get(i);
            int result = (messagePart + keyPart) % 26;
            cipheredMessage.append(cipherReversedAssignments.get(result));
        }
        System.out.println(String.format("The result of the ciphering is: %1s", cipheredMessage.toString()));
    }

    private static void decodeMessageWithKey(List<Integer> encodedKeyFragments) throws IOException {
        String messageFilePath = "src/message.txt";
        List<Integer> encodedMessageParts = readAndEncodeFile(messageFilePath);

        StringBuilder decipheredMessage = new StringBuilder();
        for (int i = 0; i < encodedMessageParts.size(); i++) {
            int messagePart = encodedMessageParts.get(i);
            int keyPart = encodedKeyFragments.get(i);
            int result = (messagePart - keyPart) % 26;
            decipheredMessage.append(cipherReversedAssignments.get(result < 0 ? 26 + result : result));
        }
        System.out.println(String.format("The result of the deciphering is: %1s", decipheredMessage.toString()));
    }

    private static List<Integer> readAndEncodeFile(String filePath) throws IOException {
        return Files.lines(Paths.get(filePath))
                .flatMap(line -> Stream.of(line.split("")))
                .map(numericCipherAssignments::get)
                .collect(Collectors.toList());
    }

}

key.txt

CIHJTUUHMLFRUGCZIBGDBQPNIPDNJGLPLLPYJYXM

message.txt

QXLATWCVZZAVLRQQLTKLTZJAQDQBASLCOTP