Construct your client as such
HostnameVerifier hostnameVerifier = HttpsURLConnection.getDefaultHostnameVerifier();
ClientConfig config = new DefaultClientConfig();
SSLContext ctx = SSLContext.getInstance("SSL");
ctx.init(null, myTrustManager, null);
config.getProperties().put(HTTPSProperties.PROPERTY_HTTPS_PROPERTIES, new HTTPSProperties(hostnameVerifier, ctx));
Client client = Client.create(config);
Ripped from this blog post with more details: http://blogs.oracle.com/enterprisetechtips/entry/consuming_restful_web_services_with
For information on setting up your certs, see this nicely answered SO question: Using HTTPS with REST in Java