Hashing files/bytes Re: RFR(JDK11/NIO) 8202285: (fs) Add a method to Files for comparing file contents (original) (raw)

forax at univ-mlv.fr forax at univ-mlv.fr
Tue May 1 22:04:14 UTC 2018

----- Mail original -----

De: "Paul Sandoz" <paul.sandoz at oracle.com> À: "Remi Forax" <forax at univ-mlv.fr> Cc: "Alan Bateman" <Alan.Bateman at oracle.com>, "nio-dev" <nio-dev at openjdk.java.net>, "core-libs-dev" <core-libs-dev at openjdk.java.net> Envoyé: Mardi 1 Mai 2018 00:37:57 Objet: Hashing files/bytes 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 <forax at univ-mlv.fr> 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

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