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https://issues.apache.org/jira/browse/NUTCH-835?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12884255#action_12884255
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Andrzej Bialecki commented on NUTCH-835:
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Yes, this is a bug. In fact the implementation makes things even worse by
appending the parsed text, contrary to its specification that says it should
use just the raw content... I'll fix this shortly.
> document deduplication (exact duplicates) failed using MD5Signature
> -------------------------------------------------------------------
>
> Key: NUTCH-835
> URL: https://issues.apache.org/jira/browse/NUTCH-835
> Project: Nutch
> Issue Type: Bug
> Affects Versions: 1.0.0, 1.1
> Environment: Linux, Ubuntu 10.04, Java 1.6.0_20
> Reporter: Sebastian Nagel
>
> The MD5Signature class calculates different signatures for identical
> documents.
> The reason is that
> byte[] data = content.getContent();
> ... StringBuilder().append(data) ...
> uses java.lang.Object.toString() to get a string representation of the
> (binary) content
> which results in unique hash codes (e.g., [...@30dc9065) even for two byte
> arrays
> with identical content.
> A solution would be to take the MD5 sum of the binary content as first part
> of the
> final signature calculation (the parsed content is the second part):
> ...
> .append(StringUtil.toHexString(MD5Hash.digest(data).getDigest())).append(parse.getText());
> Of course, there are many other solutions...
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