[LUCENE-2316] Define clear semantics for Directory.fileLength

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 3.1, 4.0-ALPHA
• Component/s: core/index
• Lucene Fields: New, Patch Available
• Assignee: Shai Erera
• Reporter: Shai Erera
• Created: 13/Mar/10 14:10
• Updated: 28/Aug/22 12:22
• Resolved: 05/May/10 20:25

Description

On this thread: http://mail-archives.apache.org/mod_mbox/lucene-java-dev/201003.mbox/[e-mail]%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:

/**
 * @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;
}

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.