One thing I don’t like about JDK is its lack of support for HTTP. Though you can make an HTTP connection using classes in the java.netpackage, it's not as easy or seamless to use open-source, third-party libraries like Apache HttpClient and HttpCore.

Though JDK 9 is bringing the support of HTTP 2.0 and better support for HTTP, I strongly suggest all Java developers get familiar with popular HTTP client libraries, including HttpClient and HttpCore.

You can also check out this post What’s New in Java 9 — Modules and More to learn more about JDK 9’s HTTP 2 support by Tim Buchalaka and his team on Udemy.