java主方法怎样实现文件加密解密

在Java中，可以使用多种算法实现文件的加密和解密。这里，我将向您展示如何使用Java内置的Cipher类来实现AES加密和解密。首先，确保已经将Java加密扩展（Java Cryptography Extension, JCE）添加到项目中。

以下是一个简单的示例，展示了如何使用AES算法对文件进行加密和解密：

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;

public class FileEncryptionDecryption {

    private static final String AES = "AES";
    private static final String CHARSET_NAME = "UTF-8";

    public static void main(String[] args) throws Exception {
        String inputFile = "input.txt";
        String encryptedFile = "encrypted.txt";
        String decryptedFile = "decrypted.txt";

        // 生成密钥
        SecretKey secretKey = generateSecretKey();

        // 加密文件
        encryptFile(inputFile, encryptedFile, secretKey);

        // 解密文件
        decryptFile(encryptedFile, decryptedFile, secretKey);
    }

    private static SecretKey generateSecretKey() throws Exception {
        KeyGenerator keyGenerator = KeyGenerator.getInstance(AES);
        keyGenerator.init(128);
        return keyGenerator.generateKey();
    }

    private static void encryptFile(String inputFile, String outputFile, SecretKey secretKey) throws Exception {
        try (FileInputStream inputStream = new FileInputStream(inputFile);
             FileOutputStream outputStream = new FileOutputStream(outputFile);
             Cipher cipher = Cipher.getInstance(AES)) {

            cipher.init(Cipher.ENCRYPT_MODE, secretKey);

            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                byte[] encryptedBytes = cipher.update(buffer, 0, bytesRead);
                if (encryptedBytes != null) {
                    outputStream.write(encryptedBytes);
                }
            }

            byte[] finalBytes = cipher.doFinal();
            if (finalBytes != null) {
                outputStream.write(finalBytes);
            }
        }
    }

    private static void decryptFile(String inputFile, String outputFile, SecretKey secretKey) throws Exception {
        try (FileInputStream inputStream = new FileInputStream(inputFile);
             FileOutputStream outputStream = new FileOutputStream(outputFile);
             Cipher cipher = Cipher.getInstance(AES)) {

            cipher.init(Cipher.DECRYPT_MODE, secretKey);

            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                byte[] decryptedBytes = cipher.update(buffer, 0, bytesRead);
                if (decryptedBytes != null) {
                    outputStream.write(decryptedBytes);
                }
            }

            byte[] finalBytes = cipher.doFinal();
            if (finalBytes != null) {
                outputStream.write(finalBytes);
            }
        }
    }
}

这个示例中，我们首先生成一个AES密钥，然后使用该密钥对文件进行加密和解密。请注意，这个示例仅用于演示目的，实际应用中可能需要更多的错误处理和功能。