Class DocsStreamer

solr/core/src/java/org/apache/solr/response/DocsStreamer.java:59–257

This streams SolrDocuments from a DocList and applies transformer

/** This streams SolrDocuments from a DocList and applies transformer */
public class DocsStreamer implements Iterator<SolrDocument> {
  /**
   * A hardcoded list of known Solr field types that will be trusted to control their own conversion
   * of stored field values into external Objects (via {@link FieldType#toObject}) when returning
   * {@link SolrDocument} instances to clients.
   *
   * <p>For historic reasons, this Set is consulted using an <em>equality</em> basis, so subclasses
   * of these "known" types are not given the same level of trust.
   *
   * <p>Any field type not found in this list will have stored values externalized as
   * <em>Strings</em> using {@link FieldType#toExternal} unless they implement {@link
   * ExternalizeStoredValuesAsObjects}
   *
   * @deprecated new field types should not be added to this list, instead use {@link
   *     ExternalizeStoredValuesAsObjects}
   */
  @Deprecated(since = "10.1")
  public static final Set<Class<? extends FieldType>> KNOWN_TYPES = new HashSet<>();

  private final ResultContext rctx;
  private final SolrDocumentFetcher docFetcher; // a collaborator of SolrIndexSearcher
  private final DocList docs;

  private final DocTransformer transformer;
  private final DocIterator docIterator;

  private final SolrReturnFields solrReturnFields;

  private int idx = -1;

  public DocsStreamer(ResultContext rctx) {
    this.rctx = rctx;
    this.docs = rctx.getDocList();
    transformer = rctx.getReturnFields().getTransformer();
    docIterator = this.docs.iterator();
    docFetcher = rctx.getDocFetcher();
    solrReturnFields = (SolrReturnFields) rctx.getReturnFields();

    if (transformer != null) {
      transformer.setContext(rctx);
    }
  }

  public int currentIndex() {
    return idx;
  }

  @Override
  public boolean hasNext() {
    return docIterator.hasNext();
  }

  @Override
  public SolrDocument next() {
    int id = docIterator.nextDoc();
    idx++;
    SolrDocument sdoc = docFetcher.solrDoc(id, solrReturnFields);