I noticed that this question has been asked but I could not find good answer
so I am posting again. Is there a good example of sorting and pagination
wtih Lucene 2.9. I have looked at Solr 1.4 source code for examples and put
together some code for testing but it's not quite working.
I have defined a collector similar to how Solr does it:
import org.apache.lucene.search.Collector;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.util.OpenBitSet;
import org.apache.lucene.index.IndexReader;
import org.apache.solr.search.BitDocSet;
import org.apache.solr.search.DocSet;
import org.apache.solr.search.SortedIntDocSet;
import java.io.IOException;
class DocSetCollector extends Collector {
private final int maxDoc;
private final int smallSetSize;
private int base;
private int numHits;
private OpenBitSet bits;
private float topscore = Float.NEGATIVE_INFINITY;
private Scorer scorer;
// in case there aren't that many hits, we may not want a very sparse
// bit array. Optimistically collect the first few docs in an array
// in case there are only a few.
final int[] scratch;
DocSetCollector(final int maxDoc) {
this(maxDoc >> 6, maxDoc);
}
DocSetCollector(final int smallSetSize, final int maxDoc) {
this.smallSetSize = smallSetSize;
this.maxDoc = maxDoc;
this.scratch = new int[smallSetSize];
}
public void collect(int doc) throws IOException {
doc += base;
if (numHits < scratch.length) {
scratch[numHits] = doc;
} else {
// this conditional could be removed if BitSet was preallocated,
but
// that
// would take up more memory, and add more GC time...
if (bits == null) {
bits = new OpenBitSet(maxDoc);
}
bits.fastSet(doc);
}
topscore = Math.max(scorer.score(), topscore);
numHits++;
}
public float getTopScore() {
return topscore;
}
public int getNumHits() {
return numHits;
}
public DocSet getDocSet() {
if (numHits <= scratch.length) {
// assumes docs were collected in sorted order!
return new SortedIntDocSet(scratch, numHits);
} else {
// set the bits for ids that were collected in the array
for (int i = 0; i < scratch.length; i++)
bits.fastSet(scratch[i]);
return new BitDocSet(bits, numHits);
}
}
public void setScorer(final Scorer scorer) throws IOException {
this.scorer = scorer;
}
public Scorer getScorer() {
return scorer;
}
public void setNextReader(IndexReader reader, int docBase)
throws IOException {
this.base = docBase;
}
public boolean acceptsDocsOutOfOrder() {
return true;
}
public int getSmallSetSize() {
return smallSetSize;
}
}
Then I defined following query methods:
private Tuple doQuery(final org.apache.lucene.search.Query query,
final Filter filter, final Sort sort, final int offset,
final int len) throws IOException {
final int maxDocRequested = Math.max(reader.maxDoc(), offset + len);
final DocSetCollector collector = new
DocSetCollector(maxDocRequested);
searcher.search(query.weight(searcher), filter, collector);
int sliceLen = collector.getNumHits(); // Math.min(maxDocRequested,
// collector.getNumHits());
if (sliceLen < 0) {
sliceLen = 0;
}
final DocList superset = sortDocSet(query, collector, sort,
sliceLen);
return new Tuple(collector.getNumHits(), superset.subset(offset,
len));
}
private DocList sortDocSet(final org.apache.lucene.search.Query query,
final DocSetCollector collector, final Sort sort, final int
nDocs)
throws IOException {
final DocSet set = collector.getDocSet();
// bit of a hack to tell if a set is sorted
boolean inOrder = set instanceof BitDocSet
|| set instanceof SortedIntDocSet;
final boolean needScores = true;
final TopDocsCollector topCollector = TopFieldCollector.create(sort,
nDocs, false, needScores, needScores, inOrder);
final int base = 0;
topCollector.setNextReader(reader, base);
DocIterator iter = set.iterator();
while (iter.hasNext()) {
int doc = iter.nextDoc();
topCollector.collect(doc - base);
}
TopDocs topDocs = topCollector.topDocs(0, nDocs);
int totalHits = topCollector.getTotalHits();
final float maxScore = totalHits > 0 ? topDocs.getMaxScore() : 0.0f;
int nDocsReturned = topDocs.scoreDocs.length;
final int[] ids = new int[nDocsReturned];
final float[] scores = new float[nDocsReturned];
for (int i = 0; i < nDocsReturned; i++) {
ScoreDoc scoreDoc = topDocs.scoreDocs[i];
ids[i] = scoreDoc.doc;
if (scores != null) {
scores[i] = scoreDoc.score;
}
}
int sliceLen = Math.min(nDocs, nDocsReturned);
if (sliceLen < 0)
sliceLen = 0;
return new DocSlice(0, sliceLen, ids, scores, topDocs.totalHits,
maxScore);
}
But I get
java.lang.NullPointerException
at
org.apache.lucene.search.TopFieldCollector$OneComparatorScoringMaxScoreCollector.collect(TopFieldCollector.java:280)
at
com.peak6.weseed.os.query.lucene.QueryImpl.sortDocSet(QueryImpl.java:677)
at
com.peak6.weseed.os.query.lucene.QueryImpl.doQuery(QueryImpl.java:649)
at
com.peak6.weseed.os.query.lucene.QueryImpl.doSearch(QueryImpl.java:402)
at com.peak6.weseed.os.query.lucene.QueryImpl.search(QueryImpl.java:179)
at
com.peak6.weseed.os.index.lucene.IndexerImplTest.query(IndexerImplTest.java:263)
It is failing because line 280 is refering scorer which is not set and per
Solr comments does not need to be setup.
Can someone suggest how to fix this?
Thanks.
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