Re: Checksum with no creation date

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.help

Date:

Sat, 26 Feb 2011 15:39:41 -0500

Message-ID:

<ikbodq$mg7$2@news.albasani.net>

On 02/26/2011 01:43 PM, Daniel Pitts wrote:

On 2/24/2011 3:45 AM, David wrote:

Hi
I want to implement a jar comparation files application using a
checksum. Two jar files should be the same if both have the same
content (although the files have different date of creation).
Comparing bytes files takes too many time and I haven't assurance
comparing only files size. So I must use a checksum algorithm.
I have tried whith CRC32 and MD5 checksums but they use the creation
file date for make the calculation. Dou you know any checksum
algorithm for do it? Or may be there's another way for make the
comparation.

MD5 and CRC32 should be hashes of data only. In theory, they shouldn't even
/care/ that they are working on a file which has metadata. Perhaps you're
using them incorrectly?

He was encountering a difference in data, not metadata, because he was hashing
the JAR file. The JAR file includes file dates in its data. It was the
representation of those dates that differed between JARs, ergo the JARs were
not the same, ergo their hashes likely differed, and in the OP's particular
case, actually did.

Had the OP compared the file-by-file hashes of the files that were copied into
the JAR, they would have had the kind of comparison they wanted.

--
Lew
Honi soit qui mal y pense.