Java 实时搜索：实用教程分享

在现代互联网时代，搜索引擎已经成为人们获取信息的主要方式之一。而对于一些需要实时性的应用场景，如在线聊天、实时监控等，则需要实时搜索技术的支持。本文将介绍 Java 实时搜索的相关技术，并提供实用的教程分享。

一、Lucene 实时搜索

Lucene 是一个高性能、全文检索引擎库，它可以被用于 Java 应用程序中。Lucene 支持实时搜索，可以在数据更新时立即响应用户的搜索请求。

1. 创建索引

首先，我们需要创建一个索引，用于存储我们要搜索的数据。下面是一个简单的示例代码：

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.document.Document;
import org.apache.lucene.document.Field;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;

public class Indexer {

    public static void main(String[] args) throws Exception {
        // 创建索引目录
        Directory directory = new RAMDirectory();

        // 创建索引写入器
        IndexWriter writer = new IndexWriter(directory, new StandardAnalyzer(), true, IndexWriter.MaxFieldLength.UNLIMITED);

        // 添加文档
        Document doc = new Document();
        doc.add(new Field("id", "1", Field.Store.YES, Field.Index.NOT_ANALYZED));
        doc.add(new Field("content", "Lucene is a high-perfORMance, full-featured text search engine library written entirely in Java.", Field.Store.YES, Field.Index.ANALYZED));
        writer.aDDDocument(doc);

        // 提交写入
        writer.commit();

        // 关闭写入器
        writer.close();
    }
}

2. 实时搜索

一旦索引创建完成，我们就可以进行实时搜索了。下面是一个简单的示例代码：

import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.IndexWriter;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.TerMQuery;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.RAMDirectory;

public class Searcher {

    public static void main(String[] args) throws Exception {
        // 创建索引目录
        Directory directory = new RAMDirectory();

        // 创建索引写入器
        IndexWriter writer = new IndexWriter(directory, new StandardAnalyzer(), true, IndexWriter.MaxFieldLength.UNLIMITED);

        // 添加文档
        Document doc = new Document();
        doc.add(new Field("id", "1", Field.Store.YES, Field.Index.NOT_ANALYZED));
        doc.add(new Field("content", "Lucene is a high-performance, full-featured text search engine library written entirely in Java.", Field.Store.YES, Field.Index.ANALYZED));
        writer.addDocument(doc);

        // 提交写入
        writer.commit();

        // 创建索引读取器
        IndexReader reader = writer.getReader();

        // 创建搜索器
        IndexSearcher searcher = new IndexSearcher(reader);

        // 创建查询
        Query query = new TermQuery(new Term("content", "Java"));

        // 执行查询
        TopDocs topDocs = searcher.search(query, 10);

        // 输出结果
        System.out.println("查询结果总数：" + topDocs.totalHits);
        for (int i = 0; i < topDocs.scoreDocs.length; i++) {
            System.out.println("文档 ID：" + topDocs.scoreDocs[i].doc + "，得分：" + topDocs.scoreDocs[i].score);
        }

        // 关闭搜索器
        searcher.close();

        // 关闭读取器
        reader.close();

        // 关闭写入器
        writer.close();
    }
}

二、elasticsearch 实时搜索

除了 Lucene，Elasticsearch 也是一个流行的实时搜索引擎。它基于 Lucene 构建，提供了更加灵活和易用的 api，同时还支持分布式搜索和数据存储。

1. 安装 Elasticsearch

首先，我们需要安装 Elasticsearch。可以从官网下载安装包，也可以使用 Docker 安装。这里介绍使用 Docker 安装的方法：

docker run -d --name elasticsearch -p 9200:9200 -p 9300:9300 elasticsearch:7.9.3

2. 创建索引

使用 Elasticsearch 创建索引非常简单，只需要向其发送一个 Http 请求即可。下面是一个简单的示例代码：

import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.elasticsearch.client.Request;
import org.elasticsearch.client.Response;
import org.elasticsearch.client.RestClient;

public class Indexer {

    public static void main(String[] args) throws Exception {
        // 创建 HTTP 客户端
        CloseableHttpClient httpClient = HttpClients.createDefault();

        // 创建索引请求
        String indexName = "my_index";
        Request request = new Request("PUT", "/" + indexName);
        String requestBody = "{
" +
                "  "mappings": {
" +
                "    "properties": {
" +
                "      "id": {
" +
                "        "type": "keyWord"
" +
                "      },
" +
                "      "content": {
" +
                "        "type": "text"
" +
                "      }
" +
                "    }
" +
                "  }
" +
                "}";
        HttpEntity entity = new StringEntity(requestBody, ContentType.APPLICATION_JSON);
        request.setEntity(entity);

        // 发送请求
        RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200, "http")).build();
        Response response = restClient.performRequest(request);

        // 输出结果
        System.out.println(response.getStatusLine().getStatusCode());
        System.out.println(response.getEntity().getContent().toString());

        // 关闭客户端
        httpClient.close();
        restClient.close();
    }
}

3. 实时搜索

使用 Elasticsearch 进行实时搜索也非常简单，只需要向其发送一个 HTTP 请求即可。下面是一个简单的示例代码：

import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.lucene.search.TotalHits;
import org.elasticsearch.client.Request;
import org.elasticsearch.client.Response;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.search.sort.ScoreSortBuilder;
import org.elasticsearch.search.sort.SortOrder;

public class Searcher {

    public static void main(String[] args) throws Exception {
        // 创建 HTTP 客户端
        CloseableHttpClient httpClient = HttpClients.createDefault();

        // 创建搜索请求
        String indexName = "my_index";
        String query = "Java";
        SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
        sourceBuilder.query(QueryBuilders.matchQuery("content", query));
        sourceBuilder.sort(new ScoreSortBuilder().order(SortOrder.DESC));
        sourceBuilder.from(0);
        sourceBuilder.size(10);
        String requestBody = sourceBuilder.toString();
        Request request = new Request("POST", "/" + indexName + "/_search");
        HttpEntity entity = new StringEntity(requestBody, ContentType.APPLICATION_jsON);
        request.setEntity(entity);

        // 发送请求
        RestClient restClient = RestClient.builder(new HttpHost("localhost", 9200, "http")).build();
        Response response = restClient.performRequest(request);

        // 输出结果
        System.out.println(response.getStatusLine().getStatusCode());
        System.out.println(response.getEntity().getContent().toString());

        // 关闭客户端
        httpClient.close();
        restClient.close();
    }
}

三、总结

本文介绍了 Java 实时搜索的相关技术，并提供了实用的教程分享。Lucene 和 Elasticsearch 都是非常流行的实时搜索引擎，它们都提供了灵活和易用的 API。在实际应用中，需要根据具体的场景选择适合自己的搜索引擎。