Elasticsearch 在 Java 中的使用教程

1. Elasticsearch 简介

Elasticsearch 是一个分布式搜索和分析引擎，基于 Apache Lucene 构建，能够实现实时数据的存储、搜索、和分析。它广泛应用于全文搜索、日志分析、性能监控等领域。Elasticsearch 的核心概念包括文档（document）、索引（index）、和分片（shard）。

2. 环境准备

2.1 安装 Elasticsearch

从 Elasticsearch 官方网站下载并安装适合你操作系统的版本。

安装完成后，通过以下命令启动 Elasticsearch 服务：

./bin/elasticsearch

默认情况下，Elasticsearch 运行在 http://localhost:9200。

2.2 Java 开发环境配置

安装 Java SDK（JDK 11 或更高版本）。
安装 Maven 或 Gradle。
创建一个 Maven 项目，添加 Elasticsearch Java 客户端的依赖。

2.3 添加 Elasticsearch 客户端依赖

在 Maven 项目的 pom.xml 文件中添加以下依赖：

<dependencies>
    <!-- Elasticsearch Java Client -->
    <dependency>
        <groupId>co.elastic.clients</groupId>
        <artifactId>elasticsearch-java</artifactId>
        <version>8.10.0</version>
    </dependency>
</dependencies>

如果你使用 Gradle，可以在 build.gradle 文件中添加以下依赖：

dependencies {
    implementation 'co.elastic.clients:elasticsearch-java:8.10.0'
}

添加依赖后，确保项目能够正常编译。

3. 使用 Java 连接 Elasticsearch

接下来，我们将编写一个简单的 Java 程序来连接 Elasticsearch。

3.1 编写连接代码

创建一个 Java 类，例如 ElasticsearchConnection.java，并编写以下代码：

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.InfoResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;

public class ElasticsearchConnection {
    public static void main(String[] args) throws Exception {
        // 创建 REST 客户端
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();

        // 创建传输层
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());

        // 创建 Elasticsearch 客户端
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 获取集群信息
        InfoResponse info = client.info();
        System.out.println("Connected to Elasticsearch cluster: " + info.clusterName());

        // 关闭客户端
        transport.close();
    }
}

3.2 运行代码

编译并运行这个程序，如果成功，你将看到类似如下的输出：

Connected to Elasticsearch cluster: elasticsearch

这表明你已经成功连接到了 Elasticsearch。

4. 基本 CRUD 操作

Elasticsearch 的 CRUD 操作主要涉及对索引中的文档进行增（Create）、查（Read）、改（Update）、删（Delete）操作。

4.1 创建索引和插入文档

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.IndexResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.IndexRequest;

public class ElasticsearchCRUD {
    public static void main(String[] args) throws Exception {
        // 创建 REST 客户端
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();

        // 创建传输层
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());

        // 创建 Elasticsearch 客户端
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 创建文档
        String json = "{ \"name\": \"John Doe\", \"age\": 30, \"city\": \"New York\" }";

        // 插入文档到索引
        IndexRequest<Object> request = new IndexRequest.Builder<>()
            .index("users")
            .id("1")
            .document(json)
            .build();

        IndexResponse response = client.index(request);
        System.out.println("Document inserted with ID: " + response.id());

        // 关闭客户端
        transport.close();
    }
}

4.2 查询文档

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.GetResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.GetRequest;

public class ElasticsearchRead {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 查询文档
        GetRequest getRequest = new GetRequest.Builder()
                .index("users")
                .id("1")
                .build();

        GetResponse<Object> response = client.get(getRequest, Object.class);
        if (response.found()) {
            System.out.println("Document found: " + response.source());
        } else {
            System.out.println("Document not found");
        }

        transport.close();
    }
}

4.3 更新文档

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.UpdateResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.UpdateRequest;

import java.util.Map;

public class ElasticsearchUpdate {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 更新文档
        Map<String, Object> updateJson = Map.of(
                "age", 31,
                "city", "San Francisco"
        );

        UpdateRequest<Object, Map<String, Object>> updateRequest = new UpdateRequest.Builder<>()
                .index("users")
                .id("1")
                .doc(updateJson)
                .build();

        UpdateResponse<Object> updateResponse = client.update(updateRequest, Object.class);
        System.out.println("Document updated: " + updateResponse.result());

        transport.close();
    }
}

4.4 删除文档

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.DeleteResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.DeleteRequest;

public class ElasticsearchDelete {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 删除文档
        DeleteRequest deleteRequest = new DeleteRequest.Builder()
                .index("users")
                .id("1")
                .build();

        DeleteResponse deleteResponse = client.delete(deleteRequest);
        System.out.println("Document deleted: " + deleteResponse.result());

        transport.close();
    }
}

5. 复杂查询操作

Elasticsearch 提供了强大的查询 DSL（Domain Specific Language），支持布尔查询、范围查询、聚合查询等。

5.1 布尔查询

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.SearchResponse;
import co.elastic.clients.elasticsearch.core.search.Hit;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.SearchRequest;
import co.elastic.clients.elasticsearch.core.search.Query;

public class ElasticsearchBooleanQuery {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 布尔查询
        SearchRequest searchRequest = new SearchRequest.Builder()
                .index("users")
                .query(Query
                .bool(b -> b
                    .must(m -> m.match(match -> match.field("name").query("John Doe")))
                    .filter(f -> f.range(r -> r.field("age").gte(30)))
                ))
                .build();

        SearchResponse<Object> searchResponse = client.search(searchRequest, Object.class);

        for (Hit<Object> hit : searchResponse.hits().hits()) {
            System.out.println("Document found: " + hit.source());
        }

        transport.close();
    }
}

5.2 范围查询

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.SearchResponse;
import co.elastic.clients.elasticsearch.core.search.Hit;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.SearchRequest;
import co.elastic.clients.elasticsearch.core.search.Query;

public class ElasticsearchRangeQuery {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 范围查询：查询 age 在 25 到 35 之间的文档
        SearchRequest searchRequest = new SearchRequest.Builder()
                .index("users")
                .query(Query.range(r -> r.field("age").gte(25).lte(35)))
                .build();

        SearchResponse<Object> searchResponse = client.search(searchRequest, Object.class);

        for (Hit<Object> hit : searchResponse.hits().hits()) {
            System.out.println("Document found: " + hit.source());
        }

        transport.close();
    }
}

6. 索引管理与优化

在 Elasticsearch 中，索引管理是非常重要的操作，合理的索引设置和优化可以大幅提升查询性能。

6.1 创建索引并设置映射

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.indices.CreateIndexResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.indices.CreateIndexRequest;

public class ElasticsearchCreateIndex {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 创建索引并设置映射
        CreateIndexRequest createIndexRequest = new CreateIndexRequest.Builder()
                .index("users")
                .mappings(m -> m
                    .properties("name", p -> p.text(t -> t))
                    .properties("age", p -> p.integer(i -> i))
                    .properties("city", p -> p.text(t -> t))
                )
                .build();

        CreateIndexResponse createIndexResponse = client.indices().create(createIndexRequest);
        if (createIndexResponse.acknowledged()) {
            System.out.println("Index created successfully!");
        }

        transport.close();
    }
}

6.2 删除索引

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.indices.DeleteIndexResponse;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.indices.DeleteIndexRequest;

public class ElasticsearchDeleteIndex {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 删除索引
        DeleteIndexRequest deleteIndexRequest = new DeleteIndexRequest.Builder()
                .index("users")
                .build();

        DeleteIndexResponse deleteIndexResponse = client.indices().delete(deleteIndexRequest);
        if (deleteIndexResponse.acknowledged()) {
            System.out.println("Index deleted successfully!");
        }

        transport.close();
    }
}

7. 聚合操作

Elasticsearch 的聚合功能非常强大，能够对数据进行分组统计、计算平均值、最大值、最小值等操作。

7.1 聚合查询：计算年龄的平均值

import co.elastic.clients.elasticsearch.ElasticsearchClient;
import co.elastic.clients.elasticsearch.core.SearchResponse;
import co.elastic.clients.elasticsearch.core.search.Hit;
import co.elastic.clients.elasticsearch.core.search.Aggregation;
import co.elastic.clients.elasticsearch.core.search.Bucket;
import co.elastic.clients.transport.rest_client.RestClientTransport;
import co.elastic.clients.json.jackson.JacksonJsonpMapper;
import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import co.elastic.clients.elasticsearch.core.SearchRequest;

public class ElasticsearchAggregation {
    public static void main(String[] args) throws Exception {
        RestClient restClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build();
        RestClientTransport transport = new RestClientTransport(
                restClient, new JacksonJsonpMapper());
        ElasticsearchClient client = new ElasticsearchClient(transport);

        // 聚合查询：计算年龄的平均值
        SearchRequest searchRequest = new SearchRequest.Builder()
                .index("users")
                .size(0)  // 不返回文档，只返回聚合结果
                .aggregations("average_age", a -> a.avg(avg -> avg.field("age")))
                .build();

        SearchResponse<Object> searchResponse = client.search(searchRequest, Object.class);

        double averageAge = searchResponse.aggregations().get("average_age").avg().value();
        System.out.println("Average age: " + averageAge);

        transport.close();
    }
}

8. 总结

本教程详细介绍了如何在 Java 中使用 Elasticsearch，涵盖了连接、基本 CRUD 操作、复杂查询、索引管理和聚合操作等方面的内容。通过这些示例，开发者可以一步步地掌握如何在 Java 项目中集成 Elasticsearch，并利用其强大的搜索和分析功能来构建高效的应用程序。