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;
      };
   };
 }