How to use

singleton

method

in

org.apache.lucene.index.DocValues

 @Override
 SortedNumericDocValues getValues(LeafReader reader, String field) throws IOException {
  NumericDocValues values = reader.getNumericDocValues(field);
  if (values == null) {
   return null;
  }
  return DocValues.singleton(values);
 }
};

 @Override
 public SortedNumericDocValues getSortedNumeric(FieldInfo field) throws IOException {
  return DocValues.singleton(valuesProducer.getNumeric(field));
 }
});

 @Override
 SortedSetDocValues getValues(LeafReader reader, String field) throws IOException {
  return DocValues.singleton(DocValues.getSorted(reader, field));
 }
};

/**
 * Returns SortedSetDocValues for the field, or {@link #emptySortedSet} if it has none. 
 * @return docvalues instance, or an empty instance if {@code field} does not exist in this reader.
 * @throws IllegalStateException if {@code field} exists, but was not indexed with docvalues.
 * @throws IllegalStateException if {@code field} has docvalues, but the type is not {@link DocValuesType#SORTED_SET}
 *                               or {@link DocValuesType#SORTED}.
 * @throws IOException if an I/O error occurs.
 */
public static SortedSetDocValues getSortedSet(LeafReader reader, String field) throws IOException {
 SortedSetDocValues dv = reader.getSortedSetDocValues(field);
 if (dv == null) {
  SortedDocValues sorted = reader.getSortedDocValues(field);
  if (sorted == null) {
   checkField(reader, field, DocValuesType.SORTED, DocValuesType.SORTED_SET);
   return emptySortedSet();
  }
  dv = singleton(sorted);
 }
 return dv;
}

/**
 * Returns SortedNumericDocValues for the field, or {@link #emptySortedNumeric} if it has none.
 * @return docvalues instance, or an empty instance if {@code field} does not exist in this reader.
 * @throws IllegalStateException if {@code field} exists, but was not indexed with docvalues.
 * @throws IllegalStateException if {@code field} has docvalues, but the type is not {@link DocValuesType#SORTED_NUMERIC}
 *                               or {@link DocValuesType#NUMERIC}.
 * @throws IOException if an I/O error occurs.
 */
public static SortedNumericDocValues getSortedNumeric(LeafReader reader, String field) throws IOException {
 SortedNumericDocValues dv = reader.getSortedNumericDocValues(field);
 if (dv == null) {
  NumericDocValues single = reader.getNumericDocValues(field);
  if (single == null) {
   checkField(reader, field, DocValuesType.SORTED_NUMERIC, DocValuesType.NUMERIC);
   return emptySortedNumeric(reader.maxDoc());
  }
  return singleton(single);
 }
 return dv;
}

SortedNumericEntry entry = sortedNumerics.get(field.name);
if (entry.numValues == entry.numDocsWithField) {
 return DocValues.singleton(getNumeric(entry));

SortedSetEntry entry = sortedSets.get(field.name);
if (entry.singleValueEntry != null) {
 return DocValues.singleton(getSorted(entry.singleValueEntry));

@Override
public SortedSetDocValues ordinals(ValuesHolder values) {
  return (SortedSetDocValues) DocValues.singleton(new Docs(this, values));
}

@Override
public SortedSetDocValues getOrdinalsValues() {
  final BytesRef term = new BytesRef(value);
  final SortedDocValues sortedValues = new AbstractSortedDocValues() {
    private int docID = -1;
    @Override
    public BytesRef lookupOrd(int ord) {
      return term;
    }
    @Override
    public int getValueCount() {
      return 1;
    }
    @Override
    public int ordValue() {
      return 0;
    }
    @Override
    public boolean advanceExact(int target) throws IOException {
      docID = target;
      return true;
    }
    @Override
    public int docID() {
      return docID;
    }
  };
  return (SortedSetDocValues) DocValues.singleton(sortedValues);
}

@Override
public SortedSetDocValues ordinals(ValuesHolder values) {
  if (multiValued) {
    return new MultiDocs(this, values);
  } else {
    return (SortedSetDocValues) DocValues.singleton(new SingleDocs(this, values));
  }
}

/**
 * Wrap the provided {@link SortedNumericDoubleValues} instance to cast all values to longs.
 */
public static SortedNumericDocValues castToLong(final SortedNumericDoubleValues values) {
  final NumericDoubleValues singleton = unwrapSingleton(values);
  if (singleton != null) {
    return DocValues.singleton(new LongCastedValues(singleton));
  } else {
    return new SortedLongCastedValues(values);
  }
}

addTermsDict(DocValues.singleton(valuesProducer.getSorted(field)));

/**
 * Given a {@link SortedNumericDoubleValues}, return a
 * {@link SortedNumericDocValues} instance that will translate double values
 * to sortable long bits using
 * {@link org.apache.lucene.util.NumericUtils#doubleToSortableLong(double)}.
 */
public static SortedNumericDocValues toSortableLongBits(SortedNumericDoubleValues values) {
  final NumericDoubleValues singleton = unwrapSingleton(values);
  if (singleton != null) {
    final NumericDocValues longBits;
    if (singleton instanceof SortableLongBitsToNumericDoubleValues) {
      longBits = ((SortableLongBitsToNumericDoubleValues) singleton).getLongValues();
    } else {
      longBits = new SortableLongBitsNumericDocValues(singleton);
    }
    return DocValues.singleton(longBits);
  } else {
    if (values instanceof SortableLongBitsToSortedNumericDoubleValues) {
      return ((SortableLongBitsToSortedNumericDoubleValues) values).getLongValues();
    } else {
      return new SortableLongBitsSortedNumericDocValues(values);
    }
  }
}

/** 
 * An empty SortedDocValues which returns {@link SortedSetDocValues#NO_MORE_ORDS} for every document 
 */
public static final RandomAccessOrds emptySortedSet() {
 return singleton(emptySorted());
}

 @Override
 SortedNumericDocValues getValues(LeafReader reader, String field) throws IOException {
  NumericDocValues values = reader.getNumericDocValues(field);
  if (values == null) {
   return null;
  }
  return DocValues.singleton(values);
 }
};

/** 
 * An empty SortedDocValues which returns {@link SortedSetDocValues#NO_MORE_ORDS} for every document 
 */
public static final RandomAccessOrds emptySortedSet() {
 return singleton(emptySorted());
}

/**
 * An empty SortedNumericDocValues which returns zero values for every document 
 */
public static final SortedNumericDocValues emptySortedNumeric(int maxDoc) {
 return singleton(emptyNumeric(), new Bits.MatchNoBits(maxDoc));
}

/**
 * An empty SortedNumericDocValues which returns zero values for every document 
 */
public static final SortedNumericDocValues emptySortedNumeric(int maxDoc) {
 return singleton(emptyNumeric(), new Bits.MatchNoBits(maxDoc));
}

/**
 * Wrap the provided {@link SortedNumericDoubleValues} instance to cast all values to longs.
 */
public static SortedNumericDocValues castToLong(final SortedNumericDoubleValues values) {
  final NumericDoubleValues singleton = unwrapSingleton(values);
  if (singleton != null) {
    return DocValues.singleton(new LongCastedValues(singleton));
  } else {
    return new SortedLongCastedValues(values);
  }
}

/**
 * Wrap the provided {SortedNumericDoubleValues} instance to cast all values to longs.
 */
public static SortedNumericDocValues castToLong(final SortedNumericDoubleValues values) {
  final NumericDoubleValues singleton = unwrapSingleton(values);
  if (singleton != null) {
    final Bits docsWithField = unwrapSingletonBits(values);
    return DocValues.singleton(new LongCastedValues(singleton), docsWithField);
  } else {
    return new SortedLongCastedValues(values);
  }
}