Example for Interface Implementations

Below is an example of the implementation of the interfaces.

Note: This example is meant for demonstration purposes only. To implement it in production, the processing should be appropriate.

@Component
 public class FileImportListenerImpl implements FileImportListener {
     @Override
     public void preProcessImportedFile(String path) throws FileProcessException {
         try {
             FileEncryptDecrypt.decryptFile(path);
         } catch (IOException | GeneralSecurityException e) {
             throw new FileProcessException(e);
         }
     }
 }

@Component
 public class FileExportListenerImpl implements FileExportListener {
     @Override
     public void postProcessExportedFile(String path) throws FileProcessException {
         try {
             FileEncryptDecrypt.encryptFile(path);
         } catch (IOException | GeneralSecurityException e) {
             throw new FileProcessException(e);
         }
     }
 }

public class FileEncryptDecrypt {


     private static final String PASS = "jS43kP77L3m2CoF";


     private static final byte[] SALT = {
             (byte) 0x43, (byte) 0x76, (byte) 0x95, (byte) 0xc7,
             (byte) 0x5b, (byte) 0xd7, (byte) 0x45, (byte) 0x17
     };


     private static final String TRANSFORMATION_ALGORITHM = "PBEWithMD5AndDES";


     private static Cipher makeCipher(boolean decryptMode) throws GeneralSecurityException {
         PBEKeySpec keySpec = new PBEKeySpec(PASS.toCharArray());
         SecretKeyFactory keyFactory = SecretKeyFactory.getInstance(TRANSFORMATION_ALGORITHM);
         SecretKey key = keyFactory.generateSecret(keySpec);
         PBEParameterSpec pbeParamSpec = new PBEParameterSpec(SALT, 42);


         Cipher cipher = Cipher.getInstance(TRANSFORMATION_ALGORITHM);
         cipher.init(decryptMode ? Cipher.DECRYPT_MODE : Cipher.ENCRYPT_MODE, key, pbeParamSpec);


         return cipher;
     }


     static void encryptFile(String fileName) throws IOException, GeneralSecurityException {
         byte[] decData;
         byte[] encData;
         File inFile = new File(fileName);
         Cipher cipher = makeCipher(false);


         try (FileInputStream inStream = new FileInputStream(inFile)) {
             int blockSize = 8;
             int paddedCount = blockSize - ((int) inFile.length() % blockSize);
             int padded = (int) inFile.length() + paddedCount;
             decData = new byte[padded];


             inStream.read(decData);


             for (int i = (int) inFile.length(); i < padded; ++i) {
                 decData[i] = (byte) paddedCount;
             }
         }


         encData = cipher.doFinal(decData);


         try (FileOutputStream outStream = new FileOutputStream(fileName)) {
             outStream.write(encData);
         }
     }


     static void decryptFile(String fileName) throws GeneralSecurityException, IOException {
         byte[] encData;
         byte[] decData;
         File inFile = new File(fileName);
         Cipher cipher = makeCipher(true);


         try (FileInputStream inStream = new FileInputStream(inFile)) {
             encData = new byte[(int) inFile.length()];
             inStream.read(encData);
             inStream.close();
             decData = cipher.doFinal(encData);


             int padCount = decData[decData.length - 1];


             if (padCount >= 1 && padCount <= 8) {
                 decData = Arrays.copyOfRange(decData, 0, decData.length - padCount);
             }
         }


         try (FileOutputStream target = new FileOutputStream(fileName)) {
             target.write(decData);
         }
     }
 }