CopyRemote::usage="CopyRemote[url, localfilename] copies a file from
an http location to localfilename.";

(* 
Example usage:
CopyRemote["http://www.mertig.com/mathdepot/buttons/ButtonTools.nb",      
ToFileName[{$UserAddOnsDirectory,"SystemFiles","FrontEnd","Palettes"},
"ButtonTools.nb"]]
*)

(* You need JLink 2.0 or higher.
 this code is based on the GetRemote example in the JLink
 documentation *)

Options[CopyRemote]={ProxyHost :> None, ProxyPort :> None};

CopyRemote[url_String /; StringMatchQ[url, "http://*.*", IgnoreCase-> True], 
localfile_:Automatic, opts___?OptionQ] :=(
Needs["JLink`"];
    JLink`JavaBlock[
        Module[{u, stream, numRead, outFile, buf, prxyHost, prxyPort},
            {prxyHost, prxyPort} = {ProxyHost, ProxyPort} /.
            Flatten[{opts}] /. Options[CopyRemote];
            JLink`StartJava[];
            If[StringQ[prxyHost],
                (* Set properties to force use of proxy. *)
                JLink`SetInternetProxy[prxyHost, prxyPort]
            ];
            u = JLink`JavaNew["java.net.URL", url];
            (* This is where the error will show up if the URL is not valid.
               A Java exception will be thrown during openStream, which
               causes the method to return $Failed.
            *)
            stream = u@openStream[];
            If[stream === $Failed, Return[$Failed]];
            buf = JLink`JavaNew["[B", 5000]; 
            (* 5000 is an arbitrary buffer size *)
            If[StringQ[localfile],
               outFile = OpenWrite[localfile, DOSTextFormat -> False],
               outFile = OpenTemporary[DOSTextFormat->False];
              ];
            While[(numRead = stream@read[buf]) > 0,
             WriteString[outFile, FromCharacterCode[If[# < 0, #+256, #]& /@
             Take[JLink`Val[buf], numRead]]]
            ];
            stream@close[];
            Close[outFile]   (* Close returns the filename *)
        ]
    ] );