在java中输出文本文件的CaesarCipher程序

Question

我正在尝试构建一个程序，它接受一个文本文件，应用CaesarCipher方法并返回和输出文件。

import java.util.*;
import java.io.*;

class CaesarCipher
{
    public static void main (String [] args) throws FileNotFoundException {
        System.out.print("What is the input file name? ");
        Scanner keyboard = new Scanner(System.in);
        String fileName = keyboard.nextLine();
        Scanner inputFile = new Scanner (new File (fileName));
        String inputFileString = inputFile.toString();
        System.out.print("What is the input file name? ");
        int s = 4;
        System.out.println("Text  : " + inputFileString);
        System.out.println("Shift : " + s);
        System.out.println("Cipher: " + encrypt(inputFileString, s));
    }

    public static String encrypt(String inputFileString, int s) {
        StringBuilder result = new StringBuilder();

        for (int i=0; i< inputFileString.length(); i++) {
            if (Character.isUpperCase(inputFileString.charAt(i))) {
                char ch = (char)(((int)inputFileString.charAt(i) + s - 65) % 26 + 65);
                result.append(ch);
            }
            else {
                char ch = (char)(((int)inputFileString.charAt(i) + s - 97) % 26 + 97);
                result.append(ch);
            }
        }

        return result.toString();
    }
}

我有两个问题：1-程序正在编译，但是当我运行它并输入文本文件名时，我收到此错误：

什么是输入文件名？文本：java.util.Scanner [delimiters = \ p {javaWhitespace} +] [position = 0] [match valid = false] [need input = false] [source closed = false] [skipped = false] [group separator = \ ，] [decimal separator =。] [positive prefix =] [negative prefix = \ Q- \ E] [positive suffix =] [negative suffix =] [NaN string = \Q \ E] [infinity string = \Q∞ \ E]

2-如何构造包含编码文本的新outPut文件？

Answer 1

您现有的代码实际上并没有将输入文件读入String。您可以使用多种方法来实现，其中一种方法是Files.readAllLines(Path)，它返回文件行的List<String>。流式传输，并使用行分隔符收集它。喜欢，

String inputFileString = Files.readAllLines(new File(fileName).toPath()).stream()
            .collect(Collectors.joining(System.lineSeparator()));

至于写入文件，请查看PrintStream(File)构造函数。

Answer 2

它适用于StringBuilder

StringBuilder inputFileString = new StringBuilder();
        while (inputFile.hasNext()) {
            String x = inputFile.nextLine();
            inputFileString.append(x);
        }

Answer 3

完全回答你的问题：

1. 您并没有以正确的方式使用扫描仪。这是一个非常好的答案，显示了how to convert an InputStream to a String的几种方式。您唯一需要知道的是如何为文件获取InputStream（请参阅下面的代码）。作为旁注，您应该始终记得关闭资源。如果不再使用，请关闭FileInputStream（more details here）。

    File file = new File("your/file/path/file.ending");
    try (FileInputStream fis = new FileInputStream(file)) {
        // your code here
    } catch (FileNotFoundException e){
        e.printStackTrace();
    }

---

2. 创建文件和向文件写入内容也有多种可能性。看看：How do I save a String to a text file using Java?

---

总而言之，我创建了一个工作示例，使用稍微不同的方式来实现caesar加密，并使用Files.lines(...)读取文件内容，并使用Files.write(...)将加密内容写入新文件：

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.Scanner;
import java.util.stream.Stream;

public class CaesarCipher {

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

        System.out.print("What is the input file name? ");
        Path filePath = Paths.get(scanner.nextLine());

        System.out.print("What is the output file name? ");
        Path encodedFilePath = Paths.get(scanner.nextLine());

        System.out.print("Caesar cipher offset? ");
        final int offset = Integer.parseInt(scanner.nextLine());

        // Retrieve a a stream of the input file, where each line is mapped using the encrypt function
        Stream<String> mappedFileStream = Files.lines(filePath).map(msg -> CaesarCipher.encrypt(msg, offset));

        // Write encrypted content to a new file using our mapped stream as an iterable
        Files.write(
                encodedFilePath,
                (Iterable<String>) mappedFileStream::iterator,
                StandardCharsets.UTF_8,
                StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);

        // Decrypt the encoded file content and print it
        Files.lines(encodedFilePath)
                .map((fileLine) -> CaesarCipher.decrypt(fileLine, offset))
                .forEach(System.out::println);
    }

    public static String encrypt(String msg, int offset) {
        offset = offset % 26 + 26;
        StringBuilder encoded = new StringBuilder(msg.length());
        for (char i : msg.toCharArray()) {
            if (Character.isLetter(i)) {
                char base = Character.isUpperCase(i) ? 'A' : 'a';
                encoded.append((char) (base + (i - base + offset) % 26));
            } else {
                encoded.append(i);
            }
        }
        return encoded.toString();
    }

    public static String decrypt(String enc, int offset) {
        return encrypt(enc, 26 - offset);
    }
}