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From "Shai Erera (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-2316) Define clear semantics for Directory.fileLength
Date Sat, 13 Mar 2010 14:11:27 GMT
Define clear semantics for Directory.fileLength
-----------------------------------------------

                 Key: LUCENE-2316
                 URL: https://issues.apache.org/jira/browse/LUCENE-2316
             Project: Lucene - Java
          Issue Type: Improvement
          Components: Index
            Reporter: Shai Erera
            Priority: Minor
             Fix For: 3.1


On this thread: http://mail-archives.apache.org/mod_mbox/lucene-java-dev/201003.mbox/%3C126142c1003121525v24499625u1589bbef4c0792e7@mail.gmail.com%3E
it was mentioned that Directory's fileLength behavior is not consistent between Directory
implementations if the given file name does not exist. FSDirectory returns a 0 length while
RAMDirectory throws FNFE.

The problem is that the semantics of fileLength() are not defined. As proposed in the thread,
we'll define the following semantics:

* Returns the length of the file denoted by <code>name</code> if the file exists.
The return value may be anything between 0 and Long.MAX_VALUE.
* Throws FileNotFoundException if the file does not exist. Note that you can call dir.fileExists(name)
if you are not sure whether the file exists or not.

For backwards we'll create a new method w/ clear semantics. Something like:

{code}
/**
 * @deprecated the method will become abstract when #fileLength(name) has been removed.
 */
public long getFileLength(String name) throws IOException {
  long len = fileLength(name);
  if (len == 0 && !fileExists(name)) {
    throw new FileNotFoundException(name);
  }
  return len;
}
{code}

The first line just calls the current impl. If it throws exception for a non-existing file,
we're ok. The second line verifies whether a 0 length is for an existing file or not and throws
an exception appropriately.

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