1. SpringBoot 项目

1.1. 添加依赖

首先在 pom.xml 中添加 ES 客户端依赖，这里 SpringBoot 使用的是 2.5.3 版本，默认会引入 ES 7.12.1 版本客户端，所以这里没有写版本号：

<dependency>
    <groupId>org.elasticsearch.client</groupId>
    <artifactId>elasticsearch-rest-high-level-client</artifactId>
</dependency>

1.2. 添加配置

在 application.properties 配置文件中添加相关 ES 集群连接信息：

#ES集群1连接
elasticsearch.connect1.hosts=192.168.50.16:9200,192.168.50.17:9200,192.168.50.18:9200
elasticsearch.connect1.username=test
elasticsearch.connect1.password=12345
#ES集群2连接
elasticsearch.connect2.hosts=192.168.50.40:9200
elasticsearch.connect2.username=test
elasticsearch.connect2.password=12345

提供一个配置类：

import lombok.Getter;
import lombok.Setter;
import org.apache.http.HttpHost;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestClientBuilder;
import org.elasticsearch.client.RestHighLevelClient;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * ES集群配置
 */
@Setter
@Configuration
@ConfigurationProperties(prefix = "elasticsearch")
public class ElasticsearchConfig {

    public static final String ES_CLIENT_1 = "es_client_1";
    public static final String ES_CLIENT_2 = "es_client_2";

    private Connect connect1;
    private Connect connect2;

    /**
     * 客户端1
     */
    @Bean(name = ES_CLIENT_1, destroyMethod = "close")
    public RestHighLevelClient restHighLevelClient1() {
        return getRestHighLevelClient(connect1);
    }

    /**
     * 客户端2
     */
    @Bean(name = ES_CLIENT_2, destroyMethod = "close")
    public RestHighLevelClient restHighLevelClient2() {
        return getRestHighLevelClient(connect2);
    }

    private RestHighLevelClient getRestHighLevelClient(Connect connect) {
        String[] hosts = connect.getHosts().split(",");
        HttpHost[] httpHosts = new HttpHost[hosts.length];
        for (int i = 0; i < hosts.length; i++) {
            httpHosts[i] = HttpHost.create(hosts[i]);
        }
        RestClientBuilder restClientBuilder = RestClient.builder(httpHosts);
        //配置身份验证
        final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
        credentialsProvider.setCredentials(AuthScope.ANY, new UsernamePasswordCredentials(connect.getUsername(), connect.getPassword()));
        restClientBuilder.setHttpClientConfigCallback(httpClientBuilder -> httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider));
        return new RestHighLevelClient(restClientBuilder);
    }

    @Setter
    @Getter
    public static class Connect {
        private String hosts;
        private String username;
        private String password;
    }

}

1.3. 使用方法

使用方法示例：

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;
import org.elasticsearch.client.RestHighLevelClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;

@Slf4j
@Service
public class SearchServiceImpl implements SearchService {

    @Autowired
    @Qualifier(ElasticsearchConfig.ES_CLIENT_1)
    private RestHighLevelClient esClient1;

    @Autowired
    @Qualifier(ElasticsearchConfig.ES_CLIENT_2)
    private RestHighLevelClient esClient2;
    
}

2. 普通 Maven 项目

2.1. 添加依赖

首先在 pom.xml 中添加 ES 客户端依赖，这里引入 ES 7.12.1 版本客户端：

<dependency>
    <groupId>org.elasticsearch.client</groupId>
    <artifactId>elasticsearch-rest-high-level-client</artifactId>
    <version>7.12.1</version>
</dependency>

1.2. 添加配置

提供一个 elasticsearch.properties 配置文件，添加相关 ES 集群连接信息：

#新闻ES集群
elasticsearch.news.hosts=192.168.50.16:9200,192.168.50.17:9200,192.168.50.18:9200
elasticsearch.news.username=test
elasticsearch.news.password=12345
#社交ES集群
elasticsearch.social.hosts=192.168.50.40:9200
elasticsearch.social.username=test
elasticsearch.social.password=12345

提供一个配置类：

import com.gtcom.constant.Constants;
import com.gtcom.constant.Separators;
import lombok.Getter;
import lombok.Setter;
import lombok.extern.slf4j.Slf4j;
import org.apache.http.HttpHost;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestClientBuilder;
import org.elasticsearch.client.RestHighLevelClient;

import java.io.IOException;
import java.util.Properties;

/**
 * ES集群配置
 */
@Slf4j
public class ElasticsearchConfig {

    @Setter
    private static Connect newsConnect = new Connect();
    @Setter
    private static Connect socialConnect = new Connect();

    private static volatile RestHighLevelClient newsEsClient;
    private static volatile RestHighLevelClient socialEsClient;

    private static final byte[] NEWS_LOCK = new byte[Constants.ZERO];
    private static final byte[] SOCIAL_LOCK = new byte[Constants.ZERO];

    static {
        Properties props = new Properties();
        try {
            props.load(ElasticsearchConfig.class.getResourceAsStream("/elasticsearch.properties"));
        } catch (IOException e) {
            log.error("load elasticsearch config properties exception", e);
        }
        String newsHost = props.getProperty("elasticsearch.news.hosts");
        String newsUserName = props.getProperty("elasticsearch.news.username");
        String newsPassword = props.getProperty("elasticsearch.news.password");
        newsConnect.setHosts(newsHost);
        newsConnect.setUsername(newsUserName);
        newsConnect.setPassword(newsPassword);
        newsEsClient = init(newsConnect);
        String socialHost = props.getProperty("elasticsearch.social.hosts");
        String socialUserName = props.getProperty("elasticsearch.social.username");
        String socialPassword = props.getProperty("elasticsearch.social.password");
        socialConnect.setHosts(socialHost);
        socialConnect.setUsername(socialUserName);
        socialConnect.setPassword(socialPassword);
        socialEsClient = init(socialConnect);
    }

    /**
     * 初始化客户端
     */
    private static RestHighLevelClient init(Connect connect) {
        String[] hosts = connect.getHosts().split(Separators.COMMA);
        HttpHost[] httpHosts = new HttpHost[hosts.length];
        for (int i = Constants.ZERO; i < hosts.length; i++) {
            httpHosts[i] = HttpHost.create(hosts[i]);
        }
        RestClientBuilder restClientBuilder = RestClient.builder(httpHosts);
        //配置身份验证
        final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
        credentialsProvider.setCredentials(AuthScope.ANY, new UsernamePasswordCredentials(connect.getUsername(), connect.getPassword()));
        restClientBuilder.setHttpClientConfigCallback(httpClientBuilder -> httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider));
        return new RestHighLevelClient(restClientBuilder);
    }

    @Setter
    @Getter
    public static class Connect {
        private String hosts;
        private String username;
        private String password;
    }

    /**
     * 获取新闻ES集群客户端
     */
    public static RestHighLevelClient getNewsEsClient() {
        if (newsEsClient == null) {
            synchronized (NEWS_LOCK) {
                if (newsEsClient == null) {
                    newsEsClient = init(newsConnect);
                    return newsEsClient;
                }
            }
        }
        return newsEsClient;
    }

    /**
     * 获取社交ES集群客户端
     */
    public static RestHighLevelClient getSocialEsClient() {
        if (socialEsClient == null) {
            synchronized (SOCIAL_LOCK) {
                if (socialEsClient == null) {
                    socialEsClient = init(socialConnect);
                    return socialEsClient;
                }
            }
        }
        return socialEsClient;
    }

}

2.3. 使用方法

使用的话可以直接通过配置类中提供的单例方法获取客户端：

RestHighLevelClient newsEsClient = ElasticsearchConfig.getNewsEsClient();
RestHighLevelClient socialEsClient = ElasticsearchConfig.getSocialEsClient();