Low Level REST Client

<dependency>
    <groupId>org.elasticsearch.client</groupId>
    <artifactId>rest</artifactId>
    <version>7.4.2</version>
</dependency>
<dependency>
	    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpasyncclient</artifactId>
    <version>4.1.4</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore-nio</artifactId>
    <version>4.4.13</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.6</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore</artifactId>
    <version>4.4.12</version>
</dependency>
<dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
    <version>1.10</version>
</dependency>
<dependency>
    <groupId>commons-logging</groupId>
    <artifactId>commons-logging</artifactId>
    <version>1.2</version>
</dependency>

import java.io.IOException;
import org.apache.http.HttpEntity;
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.entity.ContentType;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.apache.http.impl.nio.client.HttpAsyncClientBuilder;
import org.apache.http.nio.entity.NStringEntity;
import org.apache.http.util.EntityUtils;
import org.elasticsearch.client.Request;
import org.elasticsearch.client.Response;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestClientBuilder;

public class RestClientTest742 {
    public static void main(String[] args) {
        final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
        //访问用户名和密码为您创建Elasticsearch实例时设置的用户名和密码。
        credentialsProvider.setCredentials(AuthScope.ANY, new UsernamePasswordCredentials("{访问用户名}", "{访问密码}"));
        // 通过builder创建rest client，配置http client的HttpClientConfigCallback。
        // ES HTTP URL 在Baidu Elasticsearch界面中可以查询
        RestClient restClient = RestClient.builder(new HttpHost("{ES HTTP URL}", 8200))
                .setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback() {
                    @Override
                    public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpClientBuilder) {
                        return httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider);
                    }
                }).build();
        try {
            // 创建request
            Request request = new Request(
                    "POST",
                    "/{index_name}/_search");
            // 配置请求体
            request.setEntity(new NStringEntity("{\"query\":{\"match_all\":{}}}", ContentType.APPLICATION_JSON));
            Response response = restClient.performRequest(request);
            System.out.println(EntityUtils.toString(response.getEntity()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}