利用Java语言实现一个DES、AES对文件的加解密；把原始信息存在文件a.txt中，密文存在b.txt中，解密信息存在c.txt中

以下是Java语言实现DES、AES对文件的加解密的示例代码。在代码中，我们使用了Java标准库中的Cipher类来实现DES、AES算法的加解密，FileInputStream和FileOutputStream类来读写文件。

注：由于DES算法已经不安全，本示例代码中仅供学习和参考，不建议在实际应用中使用。

import javax.crypto.*;
import javax.crypto.spec.*;
import java.io.*;

public class FileEncryptor {
    
    // DES加解密密钥
    private static final byte[] DES_KEY = {0x11, 0x22, 0x4F, 0x58, (byte)0x88, 0x10, 0x40, 0x38};

    // AES加解密密钥
    private static final byte[] AES_KEY = {0x2b, 0x7e, 0x15, 0x16, 0x28, (byte)0xae, (byte)0xd2, (byte)0xa6, 
                                           (byte)0xab, 0xf7, 0x15, (byte)0x88, 0x09, (byte)0xcf, 0x4f, 0x3c};

    // DES加密文件
    public static void desEncryptFile(String srcFilePath, String destFilePath) throws Exception {
        Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
        SecretKeySpec keySpec = new SecretKeySpec(DES_KEY, "DES");
        cipher.init(Cipher.ENCRYPT_MODE, keySpec);

        FileInputStream fis = new FileInputStream(srcFilePath);
        FileOutputStream fos = new FileOutputStream(destFilePath);
        CipherOutputStream cos = new CipherOutputStream(fos, cipher);

        byte[] buffer = new byte[1024];
        int len;
        while ((len = fis.read(buffer)) != -1) {
            cos.write(buffer, 0, len);
        }

        cos.close();
        fos.close();
        fis.close();
    }

    // DES解密文件
    public static void desDecryptFile(String srcFilePath, String destFilePath) throws Exception {
        Cipher cipher = Cipher.getInstance("DES/ECB/PKCS5Padding");
        SecretKeySpec keySpec = new SecretKeySpec(DES_KEY, "DES");
        cipher.init(Cipher.DECRYPT_MODE, keySpec);

        FileInputStream fis = new FileInputStream(srcFilePath);
        CipherInputStream cis = new CipherInputStream(fis, cipher);
        FileOutputStream fos = new FileOutputStream(destFilePath);

        byte[] buffer = new byte[1024];
        int len;
        while ((len = cis.read(buffer)) != -1) {
            fos.write(buffer, 0, len);
        }

        fos.close();
        cis.close();
        fis.close();
    }

    // AES加密文件
    public static void aesEncryptFile(String srcFilePath, String destFilePath) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        SecretKeySpec keySpec = new SecretKeySpec(AES_KEY, "AES");
        IvParameterSpec ivSpec = new IvParameterSpec(AES_KEY, 0, 16);
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);

        FileInputStream fis = new FileInputStream(srcFilePath);
        FileOutputStream fos = new FileOutputStream(destFilePath);
        CipherOutputStream cos = new CipherOutputStream(fos, cipher);

        byte[] buffer = new byte[1024];
        int len;
        while ((len = fis.read(buffer)) != -1) {
            cos.write(buffer, 0, len);
        }

        cos.close();
        fos.close();
        fis.close();
    }

    // AES解密文件
    public static void aesDecryptFile(String srcFilePath, String destFilePath) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        SecretKeySpec keySpec = new SecretKeySpec(AES_KEY, "AES");
        IvParameterSpec ivSpec = new IvParameterSpec(AES_KEY, 0, 16);
        cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);

        FileInputStream fis = new FileInputStream(srcFilePath);
        CipherInputStream cis = new CipherInputStream(fis, cipher);
        FileOutputStream fos = new FileOutputStream(destFilePath);

        byte[] buffer = new byte[1024];
        int len;
        while ((len = cis.read(buffer)) != -1) {
            fos.write(buffer, 0, len);
        }

        fos.close();
        cis.close();
        fis.close();
    }

    public static void main(String[] args) throws Exception {
        // DES加密文件
        desEncryptFile("a.txt", "b_des.txt");

        // DES解密文件
        desDecryptFile("b_des.txt", "c_des.txt");

        // AES加密文件
        aesEncryptFile("a.txt", "b_aes.txt");

        // AES解密文件
        aesDecryptFile("b_aes.txt", "c_aes.txt");
    }
}

在代码中，我们定义了两个密钥：DES_KEY和AES_KEY，分别用于DES和AES算法的加解密。我们使用了Java标准库中的Cipher类来实现加解密操作，其中getInstance方法的参数指定了加密算法、工作模式和填充方式。我们使用CipherOutputStream和CipherInputStream类来实现文件的加解密，这两个类可以将加密和解密操作与文件读写操作结合起来。

在main方法中，我们分别对a.txt文件进行了DES和AES加解密操作，加密后的文件分别保存在b_des.txt和b_aes.txt中，解密后的文件分别保存在c_des.txt和c_aes.txt中。