Download ElasticSearch, then extract and start ElasticSearch with the command below:

Index data in ElasticSearch.

ElasticSearch has no indexed data, so you need to feed it. For this purpose, you will use the Wikipedia River plugin. (River is an ElasticSearch component which feeds ElasticSearch with data to index). The Wikipedia River plugin simply feeds ElasticSearch with Wikipedia pages.

Implement ElasticSearchConnector.

You now have the skeleton of the search connector.

Fetch results from ElasticSearch.

You need to call ElasticSearch to fetch Wikipedia pages based on the input parameters of the search (query text, offset, limit, sort field, sort order). ElasticSearch provides a Java Client API (TransportClient). This depends on the Lucene artifacts. Since eXo Platform already embeds the Lucene artifacts that are not necessary in the same version as the ones needed by ElasticSearch, conflicts may happen. Instead eXo will directly use the REST API:

package org.exoplatform.search.elasticsearch;


import org.apache.commons.io.IOUtils;

import org.apache.http.HttpResponse;

import org.apache.http.client.HttpClient;

import org.apache.http.client.methods.HttpPost;

import org.apache.http.entity.StringEntity;

import org.apache.http.impl.client.DefaultHttpClient;

import org.exoplatform.commons.api.search.SearchServiceConnector;

import org.exoplatform.commons.api.search.data.SearchContext;

import org.exoplatform.commons.api.search.data.SearchResult;

import org.exoplatform.container.xml.InitParams;

import org.json.simple.JSONArray;

import org.json.simple.JSONObject;

import org.json.simple.parser.JSONParser;


import java.io.StringWriter;

import java.util.*;


public class ElasticSearchConnector extends SearchServiceConnector {


  private Map<String, String> sortMapping = new HashMap<String, String>();


  public ElasticSearchConnector(InitParams initParams) {

    super(initParams);


    sortMapping.put("date", "title"); // no date field on wikipedia results

    sortMapping.put("relevancy", "_score");

    sortMapping.put("title", "title");

  }


  @Override

  public Collection<SearchResult> search(SearchContext context, String query, Collection<String> sites, int offset, int limit, String sort, String order) {

    Collection<SearchResult> results = new ArrayList<SearchResult>();


    String esQuery = "{\n" +

            "     \"from\" : " + offset + ", \"size\" : " + limit + ",\n" +

            "     \"sort\" : [\n" +

            "       { \"" + sortMapping.get(sort) + "\" : {\"order\" : \"" + order + "\"}}\n" +

            "     ],\n" +

            "     \"query\": {\n" +

            "        \"filtered\" : {\n" +

            "            \"query\" : {\n" +

            "                \"query_string\" : {\n" +

            "                    \"query\" : \"" + query + "\"\n" +

            "                }\n" +

            "            }\n" +

            "        }\n" +

            "     },\n" +

            "     \"highlight\" : {\n" +

            "       \"fields\" : {\n" +

            "         \"text\" : {\"fragment_size\" : 150, \"number_of_fragments\" : 3}\n" +

            "       }\n" +

            "     }\n" +

            "}";


    try {

      HttpClient client = new DefaultHttpClient();

      HttpPost request = new HttpPost("http://localhost:9200/_search");

      StringEntity input = new StringEntity(esQuery);

      request.setEntity(input);


      HttpResponse response = client.execute(request);

      StringWriter writer = new StringWriter();

      IOUtils.copy(response.getEntity().getContent(), writer, "UTF-8");

      String jsonResponse = writer.toString();


      JSONParser parser = new JSONParser();


      Map json = (Map)parser.parse(jsonResponse);

      JSONObject jsonResult = (JSONObject) json.get("hits");

      JSONArray jsonHits = (JSONArray) jsonResult.get("hits");

      for(Object jsonHit : jsonHits) {

        JSONObject hitSource = (JSONObject) ((JSONObject) jsonHit).get("_source");

        String title = (String) hitSource.get("title");

        JSONObject hitHighlights = (JSONObject) ((JSONObject) jsonHit).get("highlight");

        JSONArray hitHighlightsTexts = (JSONArray) hitHighlights.get("text");

        String text = "";

        for(Object hitHighlightsText : hitHighlightsTexts) {

          text += (String) hitHighlightsText + " ... ";

        }


        results.add(new SearchResult(

                "http://wikipedia.org",

                title,

                text,

                "",

                "http://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Wikipedia_svg_logo.svg/45px-Wikipedia_svg_logo.svg.png",

                new Date().getTime(),

                1

        ));

      }


    } catch (Exception e) {

      e.printStackTrace();

    }


    return results;

  }

}

Requests and responses are full JSON. You can find more details about ElasticSearch query syntax here. The important point about the search connector is that each result has to be a SearchResult object returned in a collection.

Deploy your jar (which contains the SearchConnector class and the XML configuration file) in the libs of the application server (/lib of Tomcat for example), then start eXo Platform.