From Lucene 2 to Lucene 4

Question

I'm migrating my Java application from Lucene 2 to Lucene 4, and I cannot find any good way to convert my code. I also tried to go to http://lucene.apache.org/core/4_0_0-ALPHA/MIGRATE.html but the example code in it simply does not work (for example the method reader.termDocsEnum does not exist for IndexReader or DirectoryReader , but only for AtomicReader I never heard about).

Given an IndexReader called indexReader , the old code was:

Term find = new Term("field", "value");
TermDocs td = indexReader.termDocs(find);
while (termDocs.next()) {
    Document d = termDocs.doc();
    // do stuff
}

How can I convert that code? Thanks!

Answer 1

The following should be relevant to your case:

The docs/positions enums cannot seek to a term. Instead, TermsEnum is able to seek, and then you request the docs/positions enum from that TermsEnum.

I guess you need this:

TermsEnum termsEnum = atomicReader.terms("fieldName").iterator();
BytesRef text = new BytesRef("searchTerm");
if (termsEnum.seekExact(text, true)) {
  ...
}

The low-level API is now clearly oriented towards atomic (non-composite) readers because this is the only way to top performance. You might wrap te composite reader you acquire from Directory in a SlowCompositeReaderWrapper , but, as the classname already warns, it will be slow .