Question

We’re trying to avoid saving duplicate files. However, our md5 result is always different from BlobInfo.

How we calculate it:

    MessageDigest messageDigest = java.security.MessageDigest.getInstance("MD5");
    digest = messageDigest.digest(bytes);
    String digestString = DigestUtils.md5Hex(digest);

It doesn’t match:with (new BlobInfoFactory().loadBlobInfo(blobKey)).getMd5Hash();

Example mismatches:

google vs my own calculation:
8cdeb6db94bc4fd156e2975fd8ebbcf2 vs 9003b37afbf3637de96c35774069453f 
65a25dafcba58d16d58a9c7585cc3932 vs 52383159f7d27417d50121aaee2728b5 
5cccc2d690fdc0c254234d5526876b34 vs 8196da9b6733daa60e08d927693df483 

It is on production server. ( we didn’t test dev environment )

Answer 1

Sebastian Kreft is right in the above discussion in comments.

The code I copied is wrong. it should just be:

String digestString = DigestUtils.md5Hex(bytes);

Sebastian Kreft used the trick to verify empty file’s md5 which should always be d41d8cd98f00b204e9800998ecf8427e!