// Handle error
        System.err.println("Error: " + throwable.getMessage());
    });
```

## Advanced Usage

### Index from Existing Documents

```java
import org.codelibs.fess.suggest.index.contents.document.ESSourceReader;

// Index suggestions from existing Elasticsearch documents
DocumentReader reader = new ESSourceReader(
    client,
    suggester.settings(),

 *
 * <p>Methods:</p>
 * <ul>
 *   <li>{@code get()} - Retrieves an array of elevate words from the settings.</li>
 *   <li>{@code add(ElevateWord elevateWord)} - Adds a new elevate word to the settings.</li>
 *   <li>{@code delete(String elevateWord)} - Deletes an elevate word from the settings.</li>
 *   <li>{@code deleteAll()} - Deletes all elevate words from the settings.</li>
 * </ul>
 *
 * <p>Protected Constructor:</p>
 * <ul>

         * return null; }
         */
    }

    /**
     * Gets the reading from the attribute.
     * @param stream The token stream.
     * @return The reading from the attribute.
     */
    protected String getReadingFromAttribute(final TokenStream stream) {
        return null;
        /*

import org.apache.tika.metadata.Message;
import org.apache.tika.metadata.TIFF;
import org.apache.tika.metadata.TikaCoreProperties;
import org.apache.tika.metadata.TikaMimeKeys;

/**
 * Represents extracted data from a crawled resource, including content and metadata.
 */
public class ExtractData
        implements TikaCoreProperties, CreativeCommons, Geographic, HttpHeaders, Message, ClimateForcast, TIFF, TikaMimeKeys, Serializable {

import org.opensearch.search.SearchHit;
import org.opensearch.search.sort.SortBuilder;
import org.opensearch.transport.client.Client;

/**
 * <p>
 * {@link ESSourceReader} reads documents from Elasticsearch using the scroll API.
 * It implements the {@link DocumentReader} interface to provide a way to iterate over documents
 * in a large index without loading all of them into memory at once.
 * </p>
 *
 * <p>

     * Datetime format. This format allows you to omit the time portion, if
     * desired, and use YYYY-MM-DD.
     *
     * Note that this tag is separate from the If-Modified-Since (304) header
     * the server can return, and search engines may use the information from
     * both sources differently.
     */
    private String lastmod;

    /**
     * How frequently the page is likely to change. This value provides general

     * Creates a new instance of OpenSearchAccessResultData.
     */
    public OpenSearchAccessResultData() {
    }

    /**
     * Creates a new instance of OpenSearchAccessResultData from a source map.
     * This constructor is used when loading data from OpenSearch.
     *
     * @param src The source map containing the access result data fields.
     * @throws OpenSearchAccessException if the data cannot be decoded.
     */

 * This wrapper allows for parameter management and initialization before delegating to the wrapped factory.
 *
 * The wrapper maintains its own parameter map which can be initialized separately from the wrapped factory,
 * and provides access to the wrapped factory instance through getParent().
 *
 * All crawler client management operations (adding, getting clients, setting client map) are delegated

      exercising permissions granted by this License.

      "Source" form shall mean the preferred form for making modifications,
      including but not limited to software source code, documentation
      source, and configuration files.

      "Object" form shall mean any form resulting from mechanical
      transformation or translation of a Source form, including but
      not limited to compiled object code, generated documentation,

     * @param in Input stream for a sitemap
     * @return a sitemap set
     */
    public SitemapSet parse(final InputStream in) {
        return parse(in, true);
    }

    /**
     * Parses a sitemap from the given input stream.
     * @param in the input stream to parse
     * @param recursive whether to recursively parse compressed files
     * @return the parsed sitemap set
     */