如何从 Lucene 中的文档术语向量中获取位置?

I need to iterate over all documents in a Lucene index, and obtain the positions at which each term occurs in each document. As far as I am able to understand from the Lucene javadoc, the way to do this is to do something like this:

IndexReader ir = obtainIndexReader();
Terms tv = ir.getTermVector( doc, field );
TermsEnum terms = tv.iterator();
PostingsEnum p = null;
while( terms.next() != null ) {
    p = terms.postings( p, PostingsEnum.ALL );
    while( p.nextDoc() != PostingsEnum.NO_MORE_DOCS ) {
        int freq = p.freq();
        for( int i = 0; i < freq; i++ ) {
            int pos = p.nextPosition();   // Always returns -1!!!
            BytesRef data = p.getPayload();
            doStuff( freq, pos, data ); // Fails miserably, of course.
        }
    }
}

但是，即使 (1) 索引确实包含相关字段上的位置，并且 (2) 术语向量声称具有位置(即:tv.hasPositions() == true)，我仍然得到-1" 适用于所有职位.

    FieldType ft = new FieldType();
    ft.setIndexOptions( IndexOptions.DOCS_AND_FREQS_AND_POSITIONS_AND_OFFSETS );
    ft.setStoreTermVectors( true );
    ft.setStoreTermVectorOffsets( true );
    ft.setStoreTermVectorPayloads( true );
    ft.setStoreTermVectorPositions( true );
    ft.setTokenized( true );
    return ft;