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Demo code for implementing iterative scroll queries

Last Updated: Sep 09, 2021

Demo code for implementing iterative scroll queries by using OpenSearch SDK for Java V3.1.2

Iterative scroll queries free you from having to specify the scroll ID for each scroll query.

Scroll queries do not support the aggregate, distinct, or rank clauses, and support sorting only based on a single field.

Note: Determine whether an error has occurred based on the error code and message instead of the status information. For more information about errors, see Error codes.

Demo code provided by OpenSearch SDK for Java

package com.aliyun.opensearch;

import com.aliyun.opensearch.sdk.dependencies.com.google.common.collect.Lists;
import com.aliyun.opensearch.sdk.generated.OpenSearch;
import com.aliyun.opensearch.sdk.generated.search.*;
import com.aliyun.opensearch.search.DeepPageingIterator;
import java.nio.charset.Charset;

public class testScrollIterator {

    // Scroll queries do not support the aggregate, distinct, or rank clauses, and support sorting only based on a single field.
    private static String appName = "The name of the OpenSearch application for which you want to implement iterative scroll queries";
    private static String tableName = "The name of the table to which data is to be uploaded";
    private static String accesskey = "The AccessKey ID of your Alibaba Cloud account";
    private static String secret = "The AccessKey secret of your Alibaba Cloud account";
    private static String host = "The endpoint of the OpenSearch API in your region";


    public static void main(String[] args) {

        // View documents and the default encoding format.
        System.out.println(String.format("file.encoding: %s", System.getProperty("file.encoding")));
        System.out.println(String.format("defaultCharset: %s", Charset.defaultCharset().name()));


        // Create an OpenSearch object.
        OpenSearch openSearch = new OpenSearch(accesskey, secret, host);

        // Use the OpenSearch object as a parameter to create an OpenSearchClient object.
        OpenSearchClient serviceClient = new OpenSearchClient(openSearch);

        // Use the OpenSearchClient object as a parameter to create a SearcherClient object.
        SearcherClient searcherClient = new SearcherClient(serviceClient);

        // Create a Config object and use the config clause to configure parameters such as the application name, paging-related parameters, and data format of return results.
        Config config = new Config(Lists.newArrayList(appName));

        //config.setStart(start); // The start parameter that you specify in the config clause does not take effect for scroll queries. The default value 0 is used.
        config.setHits(5);// Specify the number of documents to be displayed on each page. In this example, the number is set to 5.

        // Specify the data format of return results. Supported formats are JSON and FULLJSON. In this example, the data format is set to FULLJSON.
        config.setSearchFormat(SearchFormat.FULLJSON);

        // Specify the fields to be returned in search results.
        config.setFetchFields(Lists.newArrayList("id", "name", "phone", "int_arr", "literal_arr", "float_arr", "cate_id"));
        // Note: The rerank_size parameter in the Config class is set by the setReRankSize method of the Rank class.

        // Create a SearchParams object.
        SearchParams searchParams = new SearchParams(config);

        // Specify the query clause. You can specify multiple keywords to perform a query based on multiple index fields. In this case, you must specify the index fields in one setQuery call. If you specify each index field in a separate setQuery call, the last clause overwrites the preceding clauses.
        searchParams.setQuery("name:'opensearch'");

        // Specify a filter condition.
        //searchParams.setFilter("cate_id<=3"); // You can also set a filter condition by using the SearchParamsBuilder class.

        // Create a DeepPaging object to implement iterative scroll queries.
        DeepPaging deep =new DeepPaging();

        // Add the DeepPaging object as a query parameter.
        searchParams.setDeepPaging(deep);

        // Use the DeepPageingIterator class to implement iterative scroll queries, so that you do not need to specify scroll IDs.
        DeepPageingIterator pagesIterator = new DeepPageingIterator(searcherClient, searchParams);

        // Set an iteration interval, in milliseconds. The default interval is 100 milliseconds. This ensures that the paging speed is appropriate and does not place much pressure on the OpenSearch service. You can set an iteration interval based on your needs.
        // pagesIterator.setPagingIntervals(80);// The iteration interval, in milliseconds.

        // Determine whether an error has occurred based on the error code and message instead of the status information. For more information about errors, see the "Error codes" topic. 
        try{

            System.out.println("test");
            while (pagesIterator.hasNext()) {
                System.out.println("Debugging information: "+pagesIterator.next());
            }

        }catch(Exception ex){
            System.out.println("Error message: "+ex.getMessage());
        }

    }
}