以下是一个使用AES算法加密和解密多个文件的示例代码：

加密文件：

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.SecretKeySpec;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileEncryption {
    private static final String KEY = "your_secret_key"; // 密钥，需要保密

    public static void encryptFiles(String[] filePaths, String outputFilePath) {
        try {
            SecretKeySpec secretKey = new SecretKeySpec(KEY.getBytes(), "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, secretKey);

            FileOutputStream outputStream = new FileOutputStream(outputFilePath);
            CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, cipher);

            for (String filePath : filePaths) {
                File inputFile = new File(filePath);
                FileInputStream inputStream = new FileInputStream(inputFile);

                byte[] inputBytes = new byte[(int) inputFile.length()];
                inputStream.read(inputBytes);

                byte[] outputBytes = cipher.update(inputBytes);
                cipherOutputStream.write(outputBytes);

                inputStream.close();
            }

            byte[] finalOutputBytes = cipher.doFinal();
            cipherOutputStream.write(finalOutputBytes);

            cipherOutputStream.close();
            outputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        String[] filePaths = {"file1.txt", "file2.txt", "file3.txt"};
        String outputFilePath = "encrypted_files.enc";

        encryptFiles(filePaths, outputFilePath);
    }
}

解密文件：

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.spec.SecretKeySpec;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

public class FileDecryption {
    private static final String KEY = "your_secret_key"; // 密钥，需要保密

    public static void decryptFile(String inputFilePath, String[] outputFilePaths) {
        try {
            SecretKeySpec secretKey = new SecretKeySpec(KEY.getBytes(), "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.DECRYPT_MODE, secretKey);

            FileInputStream inputStream = new FileInputStream(inputFilePath);
            CipherInputStream cipherInputStream = new CipherInputStream(inputStream, cipher);

            for (String outputFilePath : outputFilePaths) {
                FileOutputStream outputStream = new FileOutputStream(outputFilePath);

                byte[] inputBytes = new byte[1024];
                int bytesRead;
                while ((bytesRead = cipherInputStream.read(inputBytes)) != -1) {
                    byte[] outputBytes = cipher.update(inputBytes, 0, bytesRead);
                    outputStream.write(outputBytes);
                }

                outputStream.close();
            }

            byte[] finalOutputBytes = cipher.doFinal();
            FileOutputStream finalOutputStream = new FileOutputStream(outputFilePaths[outputFilePaths.length - 1]);
            finalOutputStream.write(finalOutputBytes);
            finalOutputStream.close();

            cipherInputStream.close();
            inputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        String inputFilePath = "encrypted_files.enc";
        String[] outputFilePaths = {"dec_file1.txt", "dec_file2.txt", "dec_file3.txt"};

        decryptFile(inputFilePath, outputFilePaths);
    }
}

请注意，在这些示例代码中，我们使用AES算法和预共享密钥对文件进行加密和解密。确保将your_secret_key替换为您自己的密钥，并且密钥是安全的。此外，为了简单起见，我们使用文件名字符串数组来表示要加密/解密的文件列表，并且将所有文件内容合并到一个输出文件中。您可以根据自己的需求进行相应的修改。