开发环境：InteliJ IDEA

操作系统 ：macOS Mojave

Elasticsearch 版本：阿里云 5.5.3_with_X-Pack

客户端版本：REST Client 5.5.3

1. 预先创建好阿里云 ES 实例，开启公网地址访问白名单。

2. 预先创建好 index 和 mapping（使用 Kibana Dev Tools 创建）

PUT index_test
{
  "mappings": {
    "book": {
      "properties" : {
        "book_id" : {
          "type":"keyword"
        },
        "name" : {
          "type":"text"
        }
      }
    }
  }
}

3. 创建项目及 RestClient 类

4. pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>me.gary.es</groupId>
    <artifactId>rest-client-5</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.elasticsearch.client/rest -->
        <dependency>
            <groupId>org.elasticsearch.client</groupId>
            <artifactId>rest</artifactId>
            <version>5.5.3</version>
        </dependency>
    </dependencies>

</project>

此处的 Java REST Client Demo主要适用于阿里云ES 5.5.3版本，不兼容阿里云ES 6.3.2版本。

由于阿里云Elasticsearch实例使用5.5.3版本，所以需要您的JDK至少在 1.8 及以上版本。

5. 构建 REST Client 对象进行访问

步骤一：

由于阿里云 ES 强制要求 elasticsearch-http-basic 认证，ES 官方给出的指导是：通过 builder 构造 RestClient 对象的同时，设定 builder 的回调接口 HttpClientConfigCallback。该回调接口仅有一个实现方法 customizeHttpClient()，参数接收一个 HttpAsyncClientBuilder 对象，设置该对象的验证信息（通过 CredentialProvider），然后返回该对象。

以此方法，来给 RestClient 设置验证信息，在后续向 ES 服务端请求时，带上验证信息。

步骤二：

通过 HttpEntity，拼接 JSON 请求，通过 restClient.performRequest() 发起请求。此例主要演示：创建一条索引文档并检索该文档。

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.Response;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestClientBuilder;

import java.io.IOException;
import java.util.Collections;

public class RestClientTest {
    public static void main(String[] args) {

        // 步骤一：创建 RestClient 对象
        final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
        credentialsProvider.setCredentials(AuthScope.ANY,
                new UsernamePasswordCredentials("ES实例用户名", "ES实例密码"));
        RestClient restClient = RestClient.builder(new HttpHost("ES实例公网地址", 9200))
                .setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback() {
                    public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpClientBuilder) {
                        return httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider);
                    }
                }).build();

        // 步骤二：发起请求
        try {

            //index a document 往ES索引增加一条数据
            HttpEntity entity = new NStringEntity("{\n\"book_id\":\"0001\",\n\"name\":\"Alice in Wonderland\"\n}",
                    ContentType.APPLICATION_JSON);
            Response indexResponse = restClient.performRequest(
                    "PUT",
                    "/index_test/book/0001",
                    Collections.<String, String>emptyMap(),
                    entity);

            //search a document 检索ES数据
            Response response = restClient.performRequest("GET", "/index_test/book/0001",
                    Collections.singletonMap("pretty", "true"));
            System.out.println(EntityUtils.toString(response.getEntity()));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

该文档成功创建并检索得到，请求成功！