Using Oracle JDK instead of Open JDK

Almost all Java packages in nixpkgs use Open JDK in form of a jre dependency. If you use Oracle JDK and also want other applications to use it, you can simply tweak your .nixpkgs/config.nix so that your desired application uses Oracles JDK or JRE.

Example with UMLet with JRE 8:

{
  allowUnfree = true;
  packageOverrides = pkgs: rec {
    umlet = pkgs.umlet.override {
      jre = pkgs.oraclejre8;
    };
  };
}