为什么lucene 4.0为IndexWriter类删除了两个构造函数？

Question

there used to be three constructors, such as

IndexWriter(String, Analyzer, boolean)
IndexWriter(String, Analyzer, boolean)
IndexWriter(Directory,Analyzer, boolean)

but there is only one constructor now, which brings some inconvinence, so why the other two constructors are deleted?

is this kind of bad api design to delete the two constructors?

Answer 1

Short answer: The overall change in IndexWriter constructor strategy over time has largely been to deal with reducing the proliferation of constructor options and to better encapsulate the options being used so they could be shared & reused.

Longer Answer: The three arg constructors you are referring to (Directory/String/File, Analyzer, boolean) were deprecated in Lucene 2.4 which was released 2008-Oct-11 and then removed in Lucene 3.0 (2009-Nov-26)

Bottom Line: There was a full years notice that those constructors were eventually going away, and they were removed in a release that came out almost 3 years ago.

If you are interested in upgrading to a non-ancient version of Lucene, and your biggest complaint is that your three arg IndexWriter constructor no longer exists, then just change your code that looks like this...

IndexWriter w = new IndexWriter(dir, analyzer, true);

...so that it looks like this...

IndexWriterConfig c = new IndexWriterConfig(Version.LUCENE_36,analyzer).setOpenMode(CREATE_OR_APPEND)
IndexWriter w = new IndexWriter(dir, config);

...but i would suggest that instead of just blindly making that change, you actually look at the docs for the IndexWriterConfig and consider some of the various options that are now available.

Answer 2

Actually, there were 5 constructors (not 3) for IndexWriter in Lucene 3.0.3, the last GA release version before IndexWriterConfig came out. Here is the original ticket about the change (ie IndexWriterConfig and the deprecation for removal of the other constructors). The link to the discussion near the top of the ticket no longer works, but Nabble has a copy of it .

"Is this kind of bad api design to delete the two constructors?" That is an open-ended question that the SO FAQ says should not be asked on SO . In any case, if you want to know the Lucene developers' intentions in making a particular decision, there is no better way to find out than asking the Lucene developers directly, ie on the official Lucene mailing lists , or opening a ticket on the Lucene issue-tracking system .

If I am to speculate, here are some possibilities:

• They might have overlooked the matter or underestimated (relative to users like you because the importance is subjective) the importance of keeping the constructors.
• Keeping the constructors would have maintenance overhead. Besides making things not as "clean" (again this is subjective), the developers would have needed to maintain default settings in both IndexWriter (eg deletion policy) and IndexWriterConfig.
• Maintaining the constructor just so that users don't have to change their code has limited usefulness for the 3.0/4.0 transition. Because there are so many changes in 4.0, people cannot expect to just drop in the Lucene Core 4.0 code and expect their applications to still work.

And if you ask me, then no, I don't think it's "bad API design". It's unreasonable to expect them to keep every method call intact forever. They do have a backward compatibility policy, part of which I understand as they can deprecate whatever then want, but they won't remove or break things until the next major release. One of the worst? I think it's way better than some other popular projects that have no comparable policy and/or change behaviors (even when not fixing bugs) between point releases.