Why can't I find the truststore for an SSL handshake?

More specifically, calling this method will do the trick, so that any subsequent HttpClient calls will not care about SSL certificate validity:

public static void trustSelfSignedSSL() {
    try {
        SSLContext ctx = SSLContext.getInstance("TLS");
        X509TrustManager tm = new X509TrustManager() {

            public void checkClientTrusted(X509Certificate[] xcs, String string) throws CertificateException {
            }

            public void checkServerTrusted(X509Certificate[] xcs, String string) throws CertificateException {
            }

            public X509Certificate[] getAcceptedIssuers() {
                return null;
            }
        };
        ctx.init(null, new TrustManager[]{tm}, null);
        SSLContext.setDefault(ctx);
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

You need to properly configure the SSLContext which is done external to the RESTTemplate. This should get you started:

    String keystoreType = "JKS";
    InputStream keystoreLocation = null;
    char [] keystorePassword = null;
    char [] keyPassword = null;

    KeyStore keystore = KeyStore.getInstance(keystoreType);
    keystore.load(keystoreLocation, keystorePassword);
    KeyManagerFactory kmfactory = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());
    kmfactory.init(keystore, keyPassword);

    InputStream truststoreLocation = null;
    char [] truststorePassword = null;
    String truststoreType = "JKS";

    KeyStore truststore = KeyStore.getInstance(truststoreType);
    truststore.load(truststoreLocation, truststorePassword);
    TrustManagerFactory tmfactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());

    KeyManager [] keymanagers = kmfactory.getKeyManagers();
    TrustManager [] trustmanagers =  tmfactory.getTrustManagers();

    SSLContext sslContext = SSLContext.getInstance("TLS");
    sslContext.init(keymanagers, trustmanagers, new SecureRandom());
    SSLContext.setDefault(sslContext);