Here's another potential stacking: Define an interface ByteSequence, similar to CharSequence, as a zero-copy reference to some stored bytes somewhere. (Give it a long length.) Define bulk methods on it like hash and mismatch and transferTo. Then make File and ByteBuffer implement it. Deal with the cross-product of source and destination types underneath the interface.
(Also I want ByteSequence as a way to encapsulate resource data for class files and condy, using zero-copy methods. The types byte[] and String don't scale and require copies.) — John On May 1, 2018, at 3:04 PM, [email protected] wrote: > > ----- Mail original ----- >> De: "Paul Sandoz" <[email protected]> >> À: "Remi Forax" <[email protected]> >> Cc: "Alan Bateman" <[email protected]>, "nio-dev" >> <[email protected]>, "core-libs-dev" >> <[email protected]> >> Envoyé: Mardi 1 Mai 2018 00:37:57 >> Objet: Hashing files/bytes <was> Re: RFR(JDK11/NIO) 8202285: (fs) Add a >> method to Files for comparing file contents > >> Thanks, better then i expected with the transferTo method we recently added, >> but >> i think we could do even better for the ease of use case of “give me the hash >> of this file contents or these bytes or this byte buffer". > > yes, it can be a nice addition to java.nio.file.Files and in that case the > method that compare content can have reference in its documentation to this > new method. > >> >> Paul. > > Rémi > >> >>> On Apr 30, 2018, at 3:23 PM, Remi Forax <[email protected]> wrote: >>> >>>> >>>> To Remi’s point this might dissuade/guide developers from using this >>>> method when >>>> there are other more efficient techniques available when operating at >>>> larger >>>> scales. However, it is unfortunately harder that it should be in Java to >>>> hash >>>> the contents of a file, a byte[] or ByteBuffer, according to some chosen >>>> algorithm (or a good default). >>> >>> it's 6 lines of code >>> >>> var digest = MessageDigest.getInstance("SHA1"); >>> try(var input = Files.newInputStream(Path.of("myfile.txt")); >>> var output = new DigestOutputStream(OutputStream.nullOutputStream(), >>> digest)) { >>> input.transferTo(output); >>> } >>> var hash = digest.digest(); >>> >>> or 3 lines if you don't mind to load the whole file in memory >>> >>> var digest = MessageDigest.getInstance("SHA1"); >>> digest.update(Files.readAllBytes(Path.of("myfile.txt"))); >>> var hash = digest.digest(); >>> >>>> >>>> Paul. >>> >>> Rémi
