private int index = -1;
        private final int maxIndex = keyToIndex().size();

        @Override
        protected @Nullable Entry<K, V> computeNext() {
          for (index++; index < maxIndex; index++) {
            V value = getValue(index);
            if (value != null) {
              return immutableEntry(getKey(index), value);
            }
          }

import org.codelibs.fess.util.ComponentUtil;

/**
 * Abstract base class for document ingesters that process and transform documents
 * before they are indexed. Ingesters can be used to modify document content,
 * extract additional metadata, or perform other transformations during the
 * indexing process.
 *
 * Ingesters are processed in priority order, with lower numbers having higher priority.
 */
public abstract class Ingester {

            throws IntrospectionException {
        try {
            int index = Integer.parseInt(indexStr);

            if (value.getClass().isArray()) {
                return Array.get(value, index);
            }

            if (value instanceof List list) {
                return list.get(index);
            }
        } catch (NumberFormatException | IndexOutOfBoundsException e) {

          S extends MapWithIndexSpliterator<F, R, S>>
      implements Spliterator<R> {
    final F fromSpliterator;
    long index;

    MapWithIndexSpliterator(F fromSpliterator, long index) {
      this.fromSpliterator = fromSpliterator;
      this.index = index;
    }

    abstract S createSplit(F from, long i);

    @Override
    public @Nullable S trySplit() {

### Document Language Detection

During crawling and indexing, Fess:

1. Detects language from document content using Apache Tika
2. Validates against `supported.languages` list
3. Creates language-specific fields (e.g., `content_ja`, `title_en`, `content_sv`)
4. Applies language-specific analyzers for better search results

Configured in `fess_config.properties`:
```properties
indexer.language.fields=content,important_content,title
```

    protected volatile long executeTime = 0;

    /** List of documents waiting to be indexed */
    protected final DocList docList = new DocList();

    /** Maximum size of document requests in bytes */
    protected long maxDocumentRequestSize;

    /** Maximum number of documents to cache before indexing */
    protected int maxDocumentCacheSize;

    /** Factory for creating ingesters to process documents */

  /**
   * Returns the {@code long} value present at the given index.
   *
   * @throws IndexOutOfBoundsException if {@code index} is negative, or greater than or equal to
   *     {@link #length}
   */
  public long get(int index) {
    Preconditions.checkElementIndex(index, length());
    return array[start + index];
  }

  /**
   * Returns the smallest index for which {@link #get} returns {@code target}, or {@code -1} if no

        final String index = fessConfig.getIndexDocumentUpdateIndex();
        return deleteBySessionId(searchEngineClient, index, sessionId);
    }

    /**
     * Deletes all documents associated with the specified session ID from the given index.
     *
     * @param searchEngineClient the search engine client to use for deletion
     * @param index the index name to delete documents from

import org.codelibs.fess.util.ComponentUtil;

/**
 * Helper class for web and file system crawling and indexing operations.
 * Manages the crawling process for both web configurations and file configurations,
 * coordinating multiple crawler threads and handling indexing operations.
 */
public class WebFsIndexHelper {

    /**
     * Default constructor.
     */
    public WebFsIndexHelper() {

     * @param indexes the quantile indexes, each of which must be in the inclusive range [0, q] for
     *     q-quantiles; the order of the indexes is unimportant, duplicates will be ignored, and the
     *     set will be snapshotted when this method is called
     * @throws IllegalArgumentException if {@code indexes} is empty
     */
    public ScaleAndIndexes indexes(int... indexes) {
      return new ScaleAndIndexes(scale, indexes.clone());
    }