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https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12634998#action_12634998
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Doug Cutting commented on HADOOP-4044:
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> Many return types are changed to return this path information.
Note that only the return types in the impl methods are changed. The user
methods retain their original signatures.
> I think throwing the exception is enough [ ... ]
But a link is not an exceptional situation, it is a normal situation and should
thus be handled with normal control flow. It does not require the non-local
control flow that exceptions provide. The callee needs to pass specific
information directly back to the caller. Using a common base class is
appropriate here.
UnresolvedPathException is only used within HDFS, not in the FileSystem API.
My review has focussed on the changes to the changes to the public FileSystem
API, not to the HDFS implementation. Someone more familiar with HDFS should
review the HDFS portiions of this patch. On a cursory examination, it does
appear that this patch does use exceptions for control flow within HDFS, which
looks like a bad idea to me. Rather HDFS's internal APIs should be modified to
explicitly handle links as return values.
> Create symbolic links in HDFS
> -----------------------------
>
> Key: HADOOP-4044
> URL: https://issues.apache.org/jira/browse/HADOOP-4044
> Project: Hadoop Core
> Issue Type: New Feature
> Components: dfs
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: symLink1.patch, symLink1.patch, symLink4.patch,
> symLink5.patch, symLink6.patch
>
>
> HDFS should support symbolic links. A symbolic link is a special type of file
> that contains a reference to another file or directory in the form of an
> absolute or relative path and that affects pathname resolution. Programs
> which read or write to files named by a symbolic link will behave as if
> operating directly on the target file. However, archiving utilities can
> handle symbolic links specially and manipulate them directly.
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