Yes you need to make changes in your code. You need to load your keystore(with keypair) and if required also load your truststore into your http client. Most of the http clients require a SSLContext, so this would be sufficient for you:
KeyStore keyStore = ...;
TrustStore trustStore = ...;
KeyManagerFactory keyManagerFactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
keyManagerFactory.init(keyStore, keyStorePassword);
TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
trustManagerFactory.init(trustStore);
SSLContext sslContext = SSLContext.getInstance("TLSv1.2");
sslContext.init(keyManagerFactory.getKeyManagers(), trustManagerFactory.getTrustManagers(), null);
// Spring provides by default RestTemplate as HTTP Client, this client is an Apache HTTP Client wrapper
// The setup would be:
HttpClient httpClient = HttpClient.newBuilder();
.sslContext(sslFactory.getSslContext());
.build();
HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory();
requestFactory.setHttpClient(httpClient);
RestTemplate restTemplate = new RestTemplate(requestFactory)