ReadPrivateKey.java

// Read all bytes from the private key file
Path path = Paths.get(privateKeyFile);
byte[] bytes = Files.readAllBytes(path);

KeyFactory keyFactory = KeyFactory.getInstance("RSA");

// Generate private key object from bytes
PKCS8EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(bytes);
PrivateKey privateKey = keyFactory.generatePrivate(privateKeySpec);

// Print private key format
LOG.info(String.format("Private key format: %s", privateKey.getFormat()));