elasticsearch（六）java 使用批量查询multiGet介绍及使用

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BulkRequest是用来进行批量索引、更新、删除操作的请求对象，前面已经介绍过。

本节介绍下用来进行批量查询的操作: Mult-Get Request

1,首先创建一个主查询请求对象：

MultiGetRequest request = new MultiGetRequest();

然后依次使用主请求对象的add方法，将子查询对象加入到主查询中

request.add(new MultiGetRequest.Item("index", "type", "another_id")); 

2，可以分别针对每一个子查询进行如下设置：

1)查询的文档内容不返回：.fetchSourceContext(FetchSourceContext.DO_NOT_FETCH_SOURCE)

request.add(new MultiGetRequest.Item("posts", "doc", "2").fetchSourceContext(FetchSourceContext.DO_NOT_FETCH_SOURCE));

2) 指定查询哪些字段内容 或 过滤掉哪些字段：

String[] includes = new String[] {"user", "*r"};
String[] excludes = Strings.EMPTY_ARRAY;
FetchSourceContext fetchSourceContext = new FetchSourceContext(true, includes, excludes);
request.add(new MultiGetRequest.Item("posts2", "doc", "3").fetchSourceContext(fetchSourceContext));

3)分别指定查询的路由分片和版本等：

request.add(new MultiGetRequest.Item("posts", "doc", "with_routing")
                    .routing("some_routing"));
request.add(new MultiGetRequest.Item("index", "type", "with_parent")
                    .parent("some_parent"));
request.add(new MultiGetRequest.Item("index", "type", "with_version")
                    .versionType(VersionType.EXTERNAL)
                    .version(10123L));

注：以上设置无法在主请求中设置

3，对主请求的设置

preference, realtime and refresh 需要在主请求里设置，子请求中无法设置这些值

request.preference("some_preference");
// realtime的值默认为true
request.realtime(false);
request.refresh(true);

4，执行请求并获取结果：

MultiGetResponse response = client.mget(request, RequestOptions.DEFAULT);

5，对结果的处理及说明：

1）可以指定处理某条查询：

MultiGetItemResponse firstItem = response.getResponses()[0];

2）遍历查询的结果：

for(MultiGetItemResponse item: response.getResponses()) {
    String index = item.getIndex();
    String type = item.getType();
    String id = item.getId();
    System.out.println("第" + ++count + "条-》index:" + index + "; type:" + type + "; id:" + id);
    if(item.getFailure() != null) {
        Exception e = item.getFailure().getFailure();
        ElasticsearchException ee = (ElasticsearchException) e;
        if(ee.getMessage().contains("reason=no such index")) {
            System.out.println("查询的文档库不存在！");
        }
    }

    GetResponse getResponse = item.getResponse();

    if (getResponse.isExists()) {
        long version = getResponse.getVersion();
        String sourceAsString = getResponse.getSourceAsString();
        System.out.println("查询的结果为：");
        System.out.println(sourceAsString);
        Map<String, Object> sourceAsMap = getResponse.getSourceAsMap();
        byte[] sourceAsBytes = getResponse.getSourceAsBytes();
    } else {
        System.out.println("没有查询到相应文档");
    }
}

特殊情况说明：

1）查询的index索引库不存在时，则返回结果的failure参数不为null，含报错信息，

GetResponse getResponse = item.getResponse() 得到的getResponse值为null

故为了后面数据抛出空指针异常，要做兼容处理：

if(item.getFailure() != null) {
   Exception e = item.getFailure().getFailure();
   ElasticsearchException ee = (ElasticsearchException) e;
   if(ee.getMessage().contains("reason=no such index")) {
      System.out.println("查询的文档库不存在！");
   }
}

2）如果文档类型type或id不存在，getResponse.isExists() 的结果是false

6，完整代码示例：

package com.example.elasticsearch.document;

import org.apache.http.HttpHost;

import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.action.get.GetResponse;
import org.elasticsearch.action.get.MultiGetItemResponse;
import org.elasticsearch.action.get.MultiGetRequest;
import org.elasticsearch.action.get.MultiGetResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.common.Strings;
import org.elasticsearch.index.VersionType;
import org.elasticsearch.search.fetch.subphase.FetchSourceContext;

import java.util.Map;

/**
 * Created with IntelliJ IDEA.
 *
 * @Author: Weichang Zhong
 * @Date: 2018/11/8
 * @Time: 17:20
 * @Description:
 */
public class SynMultiGetRequest {
    public static void main(String[] args) {
        try (RestHighLevelClient client = new RestHighLevelClient(
                RestClient.builder(
                        new HttpHost("127.0.0.1", 9200, "http")
                )
        )) {
            // 创建查询父对象
            MultiGetRequest request = new MultiGetRequest();
            // 添加子查询
            request.add(new MultiGetRequest.Item("posts", "doc", "1"));
            request.add(new MultiGetRequest.Item("posts", "doc2", "2").fetchSourceContext(FetchSourceContext.DO_NOT_FETCH_SOURCE));
            String[] includes = new String[] {"user", "*r"};
            String[] excludes = Strings.EMPTY_ARRAY;
            FetchSourceContext fetchSourceContext = new FetchSourceContext(true, includes, excludes);
            request.add(new MultiGetRequest.Item("posts2", "doc", "3").fetchSourceContext(fetchSourceContext));
//            // user必须在map集合中
//            request.add(new MultiGetRequest.Item("posts", "doc", "4")
//                    .storedFields("user"));
//            MultiGetResponse response = client.mget(request, RequestOptions.DEFAULT);
//            MultiGetItemResponse item = response.getResponses()[0];
//            // user必须在map集合中
//            String value = item.getResponse().getField("user").getValue();

            // 针对每个子请求分别设置，无法在主请求中设置
            // 指定去哪个分片上查询，如何指定分片上没有，不会再去其它分片查询，如果不指定，则依次轮询各个分片查询
            request.add(new MultiGetRequest.Item("posts", "doc", "with_routing")
                    .routing("some_routing"));
            request.add(new MultiGetRequest.Item("index", "type", "with_parent")
                    .parent("some_parent"));
            request.add(new MultiGetRequest.Item("index", "type", "with_version")
                    .versionType(VersionType.EXTERNAL)
                    .version(10123L));
            // preference, realtime and refresh 需要在主请求里设置，子请求中无法设置
            request.preference("some_preference");
            // realtime的值默认为true
            request.realtime(false);
            request.refresh(true);
            MultiGetResponse response = client.mget(request, RequestOptions.DEFAULT);
            int count = 0;
            for(MultiGetItemResponse item: response.getResponses()) {
                String index = item.getIndex();
                String type = item.getType();
                String id = item.getId();
                System.out.println("第" + ++count + "条-》index:" + index + "; type:" + type + "; id:" + id);
                if(item.getFailure() != null) {
                    Exception e = item.getFailure().getFailure();
                    ElasticsearchException ee = (ElasticsearchException) e;
                    if(ee.getMessage().contains("reason=no such index")) {
                        System.out.println("查询的文档库不存在！");
                    }
                }

                GetResponse getResponse = item.getResponse();

                if (getResponse.isExists()) {
                    long version = getResponse.getVersion();
                    String sourceAsString = getResponse.getSourceAsString();
                    System.out.println("查询的结果为：");
                    System.out.println(sourceAsString);
                    Map<String, Object> sourceAsMap = getResponse.getSourceAsMap();
                    byte[] sourceAsBytes = getResponse.getSourceAsBytes();
                } else {
                    System.out.println("没有查询到相应文档");
                }
            }
        }catch (Exception e) {
            e.printStackTrace();
        }
    }
}

另外：同时也可以查询map集合中的对象，前提是对应的map集合中要存在相应的文档：

// user必须在map集合中
request.add(new MultiGetRequest.Item("posts", "doc", "4").storedFields("user"));
MultiGetResponse response = client.mget(request, RequestOptions.DEFAULT);
MultiGetItemResponse item = response.getResponses()[0];
// user必须在map集合中
String value = item.getResponse().getField("user").getValue();