Java 如何连接 ElasticSearch

在Java中连接Elasticsearch可以使用Elasticsearch提供的官方Java客户端。Elasticsearch官方提供的Java客户端有多种，其中最常用的是RestHighLevelClient。下面是使用RestHighLevelClient连接Elasticsearch的详细步骤。

1. 添加依赖

首先，在你的项目中添加Elasticsearch客户端的依赖。如果你使用的是Maven，你可以在pom.xml中添加以下依赖：

<dependencies>
    <dependency>
        <groupId>org.elasticsearch.client</groupId>
        <artifactId>elasticsearch-rest-high-level-client</artifactId>
        <version>7.10.2</version> <!-- 版本根据你使用的Elasticsearch版本选择 -->
    </dependency>
</dependencies>

如果你使用的是Gradle，你可以在build.gradle中添加以下依赖：

dependencies {
    implementation 'org.elasticsearch.client:elasticsearch-rest-high-level-client:7.10.2'
}

2. 创建客户端

接下来，在你的Java代码中创建一个连接到Elasticsearch的客户端。

import org.apache.http.HttpHost;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;

public class ElasticsearchClient {
    private static final String HOST = "localhost";
    private static final int PORT = 9200;
    private static final String SCHEME = "http";

    public static RestHighLevelClient createClient() {
        RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder(
                        new HttpHost(HOST, PORT, SCHEME)
                )
        );
        return client;
    }

    public static void closeClient(RestHighLevelClient client) {
        try {
            if (client != null) {
                client.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

3. 执行基本操作

下面是一些基本操作的示例，包括索引文档、获取文档和删除文档。

索引文档

import org.elasticsearch.action.index.IndexRequest;
import org.elasticsearch.action.index.IndexResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.common.xcontent.XContentType;

public class IndexDocument {
    public static void main(String[] args) {
        RestHighLevelClient client = ElasticsearchClient.createClient();

        IndexRequest request = new IndexRequest("my_index")
                .id("1")
                .source("{\"name\":\"John Doe\",\"age\":30,\"city\":\"New York\"}", XContentType.JSON);

        try {
            IndexResponse response = client.index(request, RequestOptions.DEFAULT);
            System.out.println(response.getId());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            ElasticsearchClient.closeClient(client);
        }
    }
}

获取文档

import org.elasticsearch.action.get.GetRequest;
import org.elasticsearch.action.get.GetResponse;
import org.elasticsearch.client.RequestOptions;

public class GetDocument {
    public static void main(String[] args) {
        RestHighLevelClient client = ElasticsearchClient.createClient();

        GetRequest getRequest = new GetRequest("my_index", "1");

        try {
            GetResponse getResponse = client.get(getRequest, RequestOptions.DEFAULT);
            if (getResponse.isExists()) {
                String sourceAsString = getResponse.getSourceAsString();
                System.out.println(sourceAsString);
            } else {
                System.out.println("Document not found");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            ElasticsearchClient.closeClient(client);
        }
    }
}

删除文档

import org.elasticsearch.action.delete.DeleteRequest;
import org.elasticsearch.action.delete.DeleteResponse;
import org.elasticsearch.client.RequestOptions;

public class DeleteDocument {
    public static void main(String[] args) {
        RestHighLevelClient client = ElasticsearchClient.createClient();

        DeleteRequest deleteRequest = new DeleteRequest("my_index", "1");

        try {
            DeleteResponse deleteResponse = client.delete(deleteRequest, RequestOptions.DEFAULT);
            System.out.println(deleteResponse.getResult());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            ElasticsearchClient.closeClient(client);
        }
    }
}

4. 处理响应

上面的示例展示了如何创建客户端并执行基本的CRUD操作。在实际应用中，你可能需要处理更多的响应和异常，例如检查响应状态，处理特定的异常等。确保根据实际需求编写相应的处理逻辑。

通过以上步骤，你可以在Java中连接并操作Elasticsearch，进行文档的索引、查询、更新和删除等操作。