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

[forax at univ-mlv.fr]

----- 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 <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 <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