说明

在明确了ES的基本概念和使用方法后，我们来学习如何使用ES的Java API.
本文假设你已经对ES的基本概念已经有了一个比较全面的认识。

客户端

你可以用Java客户端做很多事情：

• 执行标准的index,get,delete,update,search等操作。
• 在正在运行的集群上执行管理任务。

但是，通过官方文档可以得知，现在存在至少三种Java客户端。

1. Transport Client
2. Java High Level REST Client
3. Java Low Level Rest Client

造成这种混乱的原因是：

• 长久以来，ES并没有官方的Java客户端，并且Java自身是可以简单支持ES的API的，于是就先做成了TransportClient。但是TransportClient的缺点是显而易见的，它没有使用RESTful风格的接口，而是二进制的方式传输数据。

• 之后ES官方推出了Java Low Level REST Client,它支持RESTful，用起来也不错。但是缺点也很明显，因为TransportClient的使用者把代码迁移到Low Level REST Client的工作量比较大。官方文档专门为迁移代码出了一堆文档来提供参考。

• 现在ES官方推出Java High Level REST Client,它是基于Java Low Level REST Client的封装，并且API接收参数和返回值和TransportClient是一样的，使得代码迁移变得容易并且支持了RESTful的风格，兼容了这两种客户端的优点。当然缺点是存在的，就是版本的问题。ES的小版本更新非常频繁，在最理想的情况下，客户端的版本要和ES的版本一致（至少主版本号一致），次版本号不一致的话，基本操作也许可以，但是新API就不支持了。

• 强烈建议ES5及其以后的版本使用Java High Level REST Client。笔者这里使用的是ES5.6.3，下面的文章将基于JDK1.8+Spring Boot+ES5.6.3 Java High Level REST Client+Maven进行示例。

stackoverflow上的问答：
https://stackoverflow.com/questions/47031840/elasticsearchhow-to-choose-java-client/47036028#47036028

详细说明：

https://www.elastic.co/blog/the-elasticsearch-java-high-level-rest-client-is-out

参考资料：

https://www.elastic.co/guide/en/elasticsearch/client/java-rest/5.6/java-rest-high.html

Java High Level REST Client 介绍

Java High Level REST Client 是基于Java Low Level REST Client的，每个方法都可以是同步或者异步的。同步方法返回响应对象，而异步方法名以“async”结尾，并需要传入一个监听参数，来确保提醒是否有错误发生。

Java High Level REST Client需要Java1.8版本和ES。并且ES的版本要和客户端版本一致。和TransportClient接收的参数和返回值是一样的。

以下实践均是基于5.6.3的ES集群和Java High Level REST Client的。

Maven 依赖

<dependency>
    <groupId>org.elasticsearch.client</groupId> <artifactId>elasticsearch-rest-high-level-client</artifactId> <version>5.6.3</version> </dependency> 

初始化

        //Low Level Client init
        RestClient lowLevelRestClient = RestClient.builder(
                new HttpHost("localhost", 9200, "http")).build(); //High Level Client init RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); 

High Level REST Client的初始化是依赖Low Level客户端的

Index API

类似HTTP请求，Index API包括index request和index response

Index request的构造

构造一条index request的例子：

IndexRequest request = new IndexRequest(
        "posts", //index name 
        "doc",  // type "1"); // doc id String jsonString = "{" + "\"user\":\"kimchy\"," + "\"postDate\":\"2013-01-30\"," + "\"message\":\"trying out Elasticsearch\"" + "}"; request.source(jsonString, XContentType.JSON); 

注意到这里是使用的String 类型。
另一种构造的方法：

Map<String, Object> jsonMap = new HashMap<>();
jsonMap.put("user", "kimchy"); jsonMap.put("postDate", new Date()); jsonMap.put("message", "trying out Elasticsearch"); IndexRequest indexRequest = new IndexRequest("posts", "doc", "1") .source(jsonMap); //Map会自动转成JSON 

除了String和Map ,XContentBuilder 类型也是可以的：

XContentBuilder builder = XContentFactory.jsonBuilder();
builder.startObject();
{
    builder.field("user", "kimchy");
    builder.field("postDate", new Date()); builder.field("message", "trying out Elasticsearch"); } builder.endObject(); IndexRequest indexRequest = new IndexRequest("posts", "doc", "1") .source(builder); 

更直接一点的，在实例化index request对象时，可以直接给出键值对:

IndexRequest indexRequest = new IndexRequest("posts", "doc", "1")
        .source("user", "kimchy", "postDate", new Date(), "message", "trying out Elasticsearch"); 

index response的获取

同步执行

IndexResponse indexResponse = client.index(request);

异步执行

client.indexAsync(request, new ActionListener<IndexResponse>() {
    @Override
    public void onResponse(IndexResponse indexResponse) { } @Override public void onFailure(Exception e) { } }); 

需要注意的是，异步执行的方法名以Async结尾，并且多了一个Listener参数，并且需要重写回调方法。
在kibana控制台查询得到数据：

{
  "_index": "posts",
  "_type": "doc",
  "_id": "1", "_version": 1, "found": true, "_source": { "user": "kimchy", "postDate": "2017-11-01T05:48:26.648Z", "message": "trying out Elasticsearch" } } 

index request中的数据已经成功入库。

index response的返回值操作

client.index()方法返回值类型为IndexResponse,我们可以用它来进行如下操作：

String index = indexResponse.getIndex();  //index名称，类型等信息
String type = indexResponse.getType(); 
String id = indexResponse.getId();
long version = indexResponse.getVersion();
if (indexResponse.getResult() == DocWriteResponse.Result.CREATED) { } else if (indexResponse.getResult() == DocWriteResponse.Result.UPDATED) { } ShardInfo shardInfo = indexResponse.getShardInfo(); //对分片使用的判断 if (shardInfo.getTotal() != shardInfo.getSuccessful()) { } if (shardInfo.getFailed() > 0) { for (ReplicationResponse.ShardInfo.Failure failure : shardInfo.getFailures()) { String reason = failure.reason(); } } 

对version冲突的判断：

IndexRequest request = new IndexRequest("posts", "doc", "1")
        .source("field", "value") .version(1); try { IndexResponse response = client.index(request); } catch(ElasticsearchException e) { if (e.status() == RestStatus.CONFLICT) { } } 

对index动作的判断：

IndexRequest request = new IndexRequest("posts", "doc", "1")
        .source("field", "value") .opType(DocWriteRequest.OpType.CREATE);//create or update try { IndexResponse response = client.index(request); } catch(ElasticsearchException e) { if (e.status() == RestStatus.CONFLICT) { } } 

GET API

GET request

GetRequest getRequest = new GetRequest(
        "posts",//index name 
        "doc",  //type "1"); //id 

GET response

同步方法：

GetResponse getResponse = client.get(getRequest);

异步方法：

client.getAsync(request, new ActionListener<GetResponse>() {
    @Override
    public void onResponse(GetResponse getResponse) { } @Override public void onFailure(Exception e) { } }); 

对返回对象的操作：

String index = getResponse.getIndex();
String type = getResponse.getType();
String id = getResponse.getId();
if (getResponse.isExists()) {
    long version = getResponse.getVersion();
    String sourceAsString = getResponse.getSourceAsString(); Map<String, Object> sourceAsMap = getResponse.getSourceAsMap(); byte[] sourceAsBytes = getResponse.getSourceAsBytes(); } else { //TODO } 

异常处理：

GetRequest request = new GetRequest("does_not_exist", "doc", "1");
try { GetResponse getResponse = client.get(request); } catch (ElasticsearchException e) { if (e.status() == RestStatus.NOT_FOUND) { } if (e.status() == RestStatus.CONFLICT) { } } 

DELETE API

与Index API和 GET API及其相似

DELETE request

DeleteRequest request = new DeleteRequest(
        "posts",    
        "doc",     
        "1");      

DELETE response

同步：

DeleteResponse deleteResponse = client.delete(request);

异步:

client.deleteAsync(request, new ActionListener<DeleteResponse>() {
    @Override
    public void onResponse(DeleteResponse deleteResponse) { } @Override public void onFailure(Exception e) { } }); 

Update API

update request

UpdateRequest updateRequest = new UpdateRequest(
        "posts", 
        "doc",  
        "1");   

update脚本：
在之前我们介绍了如何使用简单的脚本来更新数据

POST /posts/doc/1/_update?pretty
{
  "script" : "ctx._source.age += 5"
}

也可以写成:

POST /posts/doc/1/_update?pretty
{
  "script" : {
    "lang":"painless",
    "source":"ctx._source.age += 5" } } 

对应代码：

        UpdateRequest updateRequest = new UpdateRequest("posts", "doc", "1");
        Map<String, Object> parameters = new HashMap<>(); parameters.put("age", 4); Script inline = new Script(ScriptType.INLINE, "painless", "ctx._source.age += params.age", parameters); updateRequest.script(inline); try { UpdateResponse updateResponse = client.update(updateRequest); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } 

使用部分文档更新

1. String

        String jsonString = "{" +
                "\"updated\":\"2017-01-02\"," +
                "\"reason\":\"easy update\"" +
                "}"; updateRequest.doc(jsonString, XContentType.JSON); try { client.update(updateRequest); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } 

2.Map

        Map<String, Object> jsonMap = new HashMap<>();
        jsonMap.put("updated", new Date()); jsonMap.put("reason", "dailys update"); UpdateRequest updateRequest = new UpdateRequest("posts", "doc", "1").doc(jsonMap); try { client.update(updateRequest); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } 

3.XContentBuilder

    try {
            XContentBuilder builder = XContentFactory.jsonBuilder();
            builder.startObject();
            {
                builder.field("updated", new Date());
                System.out.println(new Date()); builder.field("reason", "daily update"); } builder.endObject(); UpdateRequest request = new UpdateRequest("posts", "doc", "1") .doc(builder); client.update(request); } catch (IOException e) { // TODO: handle exception } 

4.键值对

    try {
            UpdateRequest request = new UpdateRequest("posts", "doc", "1") .doc("updated", new Date(), "reason", "daily updatesss"); client.update(request); } catch (IOException e) { // TODO: handle exception } 

upsert

如果文档不存在，可以使用upsert来生成这个文档。

String jsonString = "{\"created\":\"2017-01-01\"}";
request.upsert(jsonString, XContentType.JSON);

同样地，upsert可以接Map,Xcontent，键值对参数。

update response

同样地，update response可以是同步的，也可以是异步的

同步执行:

UpdateResponse updateResponse = client.update(request);

异步执行：

   client.updateAsync(request, new ActionListener<UpdateResponse>() {
    @Override
    public void onResponse(UpdateResponse updateResponse) { } @Override public void onFailure(Exception e) { } }); 

与其他response类似，update response返回对象可以进行各种判断操作，这里不再赘述。

Bulk API

Bulk request

之前的文档说明过，bulk接口是批量index/update/delete操作
在API中，只需要一个bulk request就可以完成一批请求。

BulkRequest request = new BulkRequest(); 
request.add(new IndexRequest("posts", "doc", "1") .source(XContentType.JSON,"field", "foo")); request.add(new IndexRequest("posts", "doc", "2") .source(XContentType.JSON,"field", "bar")); request.add(new IndexRequest("posts", "doc", "3") .source(XContentType.JSON,"field", "baz")); 

• 注意，Bulk API只接受JSON和SMILE格式.其他格式的数据将会报错。
• 不同类型的request可以写在同一个bulk request里。

BulkRequest request = new BulkRequest();
request.add(new DeleteRequest("posts", "doc", "3")); request.add(new UpdateRequest("posts", "doc", "2") .doc(XContentType.JSON,"other", "test")); request.add(new IndexRequest("posts", "doc", "4") .source(XContentType.JSON,"field", "baz")); 

bulk response

同步执行:

BulkResponse bulkResponse = client.bulk(request);

异步执行：

client.bulkAsync(request, new ActionListener<BulkResponse>() {
    @Override
    public void onResponse(BulkResponse bulkResponse) { } @Override public void onFailure(Exception e) { } }); 

对response的处理与其他类型的response十分类似，在这不再赘述。

bulk processor

BulkProcessor 简化bulk API的使用，并且使整个批量操作透明化。
BulkProcessor 的执行需要三部分组成：

1. RestHighLevelClient :执行bulk请求并拿到响应对象。
2. BulkProcessor.Listener：在执行bulk request之前、之后和当bulk response发生错误时调用。
3. ThreadPool：bulk request在这个线程池中执行操作，这使得每个请求不会被挡住，在其他请求正在执行时，也可以接收新的请求。

示例代码：

        Settings settings = Settings.EMPTY; 
        ThreadPool threadPool = new ThreadPool(settings); //构建新的线程池
        BulkProcessor.Listener listener = new BulkProcessor.Listener() { 
            //构建bulk listener

            @Override public void beforeBulk(long executionId, BulkRequest request) { //重写beforeBulk,在每次bulk request发出前执行,在这个方法里面可以知道在本次批量操作中有多少操作数 int numberOfActions = request.numberOfActions(); logger.debug("Executing bulk [{}] with {} requests", executionId, numberOfActions); } @Override public void afterBulk(long executionId, BulkRequest request, BulkResponse response) { //重写afterBulk方法，每次批量请求结束后执行，可以在这里知道是否有错误发生。 if (response.hasFailures()) { logger.warn("Bulk [{}] executed with failures", executionId); } else { logger.debug("Bulk [{}] completed in {} milliseconds", executionId, response.getTook().getMillis()); } } @Override public void afterBulk(long executionId, BulkRequest request, Throwable failure) { //重写方法，如果发生错误就会调用。 logger.error("Failed to execute bulk", failure); } }; BulkProcessor.Builder builder = new BulkProcessor.Builder(client::bulkAsync, listener, threadPool);//使用builder做批量操作的控制 BulkProcessor bulkProcessor = builder.build(); //在这里调用build()方法构造bulkProcessor,在底层实际上是用了bulk的异步操作 builder.setBulkActions(500); //执行多少次动作后刷新bulk.默认1000，-1禁用 builder.setBulkSize(new ByteSizeValue(1L, ByteSizeUnit.MB));//执行的动作大小超过多少时，刷新bulk。默认5M，-1禁用 builder.setConcurrentRequests(0);//最多允许多少请求同时执行。默认是1，0是只允许一个。 builder.setFlushInterval(TimeValue.timeValueSeconds(10L));//设置刷新bulk的时间间隔。默认是不刷新的。 builder.setBackoffPolicy(BackoffPolicy.constantBackoff(TimeValue.timeValueSeconds(1L), 3)); //设置补偿机制参数。由于资源限制（比如线程池满），批量操作可能会失败，在这定义批量操作的重试次数。 //新建三个 index 请求 IndexRequest one = new IndexRequest("posts", "doc", "1"). source(XContentType.JSON, "title", "In which order are my Elasticsearch queries executed?"); IndexRequest two = new IndexRequest("posts", "doc", "2") .source(XContentType.JSON, "title", "Current status and upcoming changes in Elasticsearch"); IndexRequest three = new IndexRequest("posts", "doc", "3") .source(XContentType.JSON, "title", "The Future of Federated Search in Elasticsearch"); //新的三条index请求加入到上面配置好的bulkProcessor里面。 bulkProcessor.add(one); bulkProcessor.add(two); bulkProcessor.add(three); // add many request here. //bulkProcess必须被关闭才能使上面添加的操作生效 bulkProcessor.close(); //立即关闭 //关闭bulkProcess的两种方法： try { //2.调用awaitClose. //简单来说，就是在规定的时间内，是否所有批量操作完成。全部完成，返回true,未完成返//回false boolean terminated = bulkProcessor.awaitClose(30L, TimeUnit.SECONDS); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } 

Search API

Search request

Search API提供了对文档的查询和聚合的查询。
它的基本形式:

SearchRequest searchRequest = new SearchRequest();  //构造search request .在这里无参，查询全部索引
SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();//大多数查询参数要写在searchSourceBuilder里 
searchSourceBuilder.query(QueryBuilders.matchAllQuery());//增加match_all的条件。 

SearchRequest searchRequest = new SearchRequest("posts"); //指定posts索引
searchRequest.types("doc"); //指定doc类型 

使用SearchSourceBuilder

大多数的查询控制都可以使用SearchSourceBuilder实现。
举一个简单例子:

SearchSourceBuilder sourceBuilder = new SearchSourceBuilder(); //构造一个默认配置的对象
sourceBuilder.query(QueryBuilders.termQuery("user", "kimchy")); //设置查询 sourceBuilder.from(0); //设置从哪里开始 sourceBuilder.size(5); //每页5条 sourceBuilder.timeout(new TimeValue(60, TimeUnit.SECONDS)); //设置超时时间 

配置好searchSourceBuilder后，将它传入searchRequest里：

SearchRequest searchRequest = new SearchRequest();
searchRequest.source(sourceBuilder);

建立查询

在上面的例子，我们注意到，sourceBuilder构造查询条件时，使用QueryBuilders对象.
在所有ES查询中，它存在于所有ES支持的查询类型中。
使用它的构造体来创建:

MatchQueryBuilder matchQueryBuilder = new MatchQueryBuilder("user", "kimchy");

这里的代码相当于：

 "query": { "match": { "user": "kimchy" } }

相关设置：

matchQueryBuilder.fuzziness(Fuzziness.AUTO);  //是否模糊查询
matchQueryBuilder.prefixLength(3); //设置前缀长度
matchQueryBuilder.maxExpansions(10);//设置最大膨胀系数 ？？？ 

QueryBuilder还可以使用 QueryBuilders工具类来创造，编程体验比较顺畅：

QueryBuilder matchQueryBuilder = QueryBuilders.matchQuery("user", "kimchy")
                                                .fuzziness(Fuzziness.AUTO)
                                                .prefixLength(3)
                                                .maxExpansions(10);

无论QueryBuilder对象是如何创建的，都要将它传入SearchSourceBuilder里面：

searchSourceBuilder.query(matchQueryBuilder);

在之前导入的account数据中，使用match的示例代码:

GET /bank/_search?pretty
{
  "query": {
    "match": {
      "firstname": "Virginia"  
   }
  }
}

JAVA:

    @Test
    public void test2(){ RestClient lowLevelRestClient = RestClient.builder( new HttpHost("172.16.73.50", 9200, "http")).build(); RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); SearchRequest searchRequest = new SearchRequest("bank"); searchRequest.types("account"); SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder(); MatchQueryBuilder mqb = QueryBuilders.matchQuery("firstname", "Virginia"); searchSourceBuilder.query(mqb); searchRequest.source(searchSourceBuilder); try { SearchResponse searchResponse = client.search(searchRequest); System.out.println(searchResponse.toString()); } catch (IOException e) { e.printStackTrace(); } } 

排序

SearchSourceBuilder可以添加一种或多种SortBuilder。
有四种特殊的排序实现：

• field
• score
• GeoDistance
• scriptSortBuilder

sourceBuilder.sort(new ScoreSortBuilder().order(SortOrder.DESC)); //按照score倒序排列
sourceBuilder.sort(new FieldSortBuilder("_uid").order(SortOrder.ASC));  //并且按照id正序排列 

过滤

默认情况下，searchRequest返回文档内容，与REST API一样，这里你可以重写search行为。例如，你可以完全关闭"_source"检索。

sourceBuilder.fetchSource(false);

该方法还接受一个或多个通配符模式的数组，以更细粒度地控制包含或排除哪些字段。

String[] includeFields = new String[] {"title", "user", "innerObject.*"}; String[] excludeFields = new String[] {"_type"}; sourceBuilder.fetchSource(includeFields, excludeFields); 

聚合请求

通过配置适当的 AggregationBuilder ，再将它传入SearchSourceBuilder里,就可以完成聚合请求了。
之前的文档里面，我们通过下面这条命令，导入了一千条account信息:

curl -H "Content-Type: application/json" -XPOST ''localhost:9200/bank/account/_bulk?pretty&refresh'' --data-binary "@accounts.json"

随后，我们介绍了如何通过聚合请求进行分组:

GET /bank/_search?pretty
{
  "size": 0,
  "aggs": {
    "group_by_state": {
      "terms": {
        "field": "state.keyword" } } } } 

我们将这一千条数据根据state字段分组，得到响应：

{
  "took": 2,
  "timed_out": false,
  "_shards": { "total": 5, "successful": 5, "skipped": 0, "failed": 0 }, "hits": { "total": 999, "max_score": 0, "hits": [] }, "aggregations": { "group_by_state": { "doc_count_error_upper_bound": 20, "sum_other_doc_count": 770, "buckets": [ { "key": "ID", "doc_count": 27 }, { "key": "TX", "doc_count": 27 }, { "key": "AL", "doc_count": 25 }, { "key": "MD", "doc_count": 25 }, { "key": "TN", "doc_count": 23 }, { "key": "MA", "doc_count": 21 }, { "key": "NC", "doc_count": 21 }, { "key": "ND", "doc_count": 21 }, { "key": "MO", "doc_count": 20 }, { "key": "AK", "doc_count": 19 } ] } } } 

Java实现:

    @Test
    public void test2(){ RestClient lowLevelRestClient = RestClient.builder( new HttpHost("172.16.73.50", 9200, "http")).build(); RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); SearchRequest searchRequest = new SearchRequest("bank"); searchRequest.types("account"); TermsAggregationBuilder aggregation = AggregationBuilders.terms("group_by_state") .field("state.keyword"); SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder(); searchSourceBuilder.aggregation(aggregation); searchSourceBuilder.size(0); searchRequest.source(searchSourceBuilder); try { SearchResponse searchResponse = client.search(searchRequest); System.out.println(searchResponse.toString()); } catch (IOException e) { e.printStackTrace(); } } 

输出:

{"took":4,"timed_out":false,"_shards":{"total":5,"successful":5,"skipped":0,"failed":0},"hits":{"total":999,"max_score":0.0,"hits":[]},"aggregations":{"sterms#group_by_state":{"doc_count_error_upper_bound":20,"sum_other_doc_count":770,"buckets":[{"key":"ID","doc_count":27},{"key":"TX","doc_count":27},{"key":"AL","doc_count":25},{"key":"MD","doc_count":25},{"key":"TN","doc_count":23},{"key":"MA","doc_count":21},{"key":"NC","doc_count":21},{"key":"ND","doc_count":21},{"key":"MO","doc_count":20},{"key":"AK","doc_count":19}]}}} 

同步执行

SearchResponse searchResponse = client.search(searchRequest);

异步执行

client.searchAsync(searchRequest, new ActionListener<SearchResponse>() {
    @Override
    public void onResponse(SearchResponse searchResponse) { } @Override public void onFailure(Exception e) { } }); 

Search response

Search response返回对象与其在API里的一样，返回一些元数据和文档数据。
首先，返回对象里的数据十分重要，因为这是查询的返回结果、使用分片情况、文档数据,HTTP状态码等

RestStatus status = searchResponse.status();
TimeValue took = searchResponse.getTook();
Boolean terminatedEarly = searchResponse.isTerminatedEarly();
boolean timedOut = searchResponse.isTimedOut();

其次，返回对象里面包含关于分片的信息和分片失败的处理:

int totalShards = searchResponse.getTotalShards();
int successfulShards = searchResponse.getSuccessfulShards();
int failedShards = searchResponse.getFailedShards();
for (ShardSearchFailure failure : searchResponse.getShardFailures()) {
    // failures should be handled here } 

取回searchHit

为了取回文档数据，我们要从search response的返回对象里先得到searchHit对象。

SearchHits hits = searchResponse.getHits();

取回文档数据：

    @Test
    public void test2(){ RestClient lowLevelRestClient = RestClient.builder( new HttpHost("172.16.73.50", 9200, "http")).build(); RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); SearchRequest searchRequest = new SearchRequest("bank"); searchRequest.types("account"); SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder(); searchRequest.source(searchSourceBuilder); try { SearchResponse searchResponse = client.search(searchRequest); SearchHits searchHits = searchResponse.getHits(); SearchHit[] searchHit = searchHits.getHits(); for (SearchHit hit : searchHit) { System.out.println(hit.getSourceAsString()); } } catch (IOException e) { e.printStackTrace(); } } 

根据需要，还可以转换成其他数据类型:

String sourceAsString = hit.getSourceAsString();
Map<String, Object> sourceAsMap = hit.getSourceAsMap();
String documentTitle = (String) sourceAsMap.get("title"); List<Object> users = (List<Object>) sourceAsMap.get("user"); Map<String, Object> innerObject = (Map<String, Object>) sourceAsMap.get("innerObject"); 

取回聚合数据

聚合数据可以通过SearchResponse返回对象，取到它的根节点，然后再根据名称取到聚合数据。

GET /bank/_search?pretty
{
  "size": 0,
  "aggs": {
    "group_by_state": {
      "terms": {
        "field": "state.keyword" } } } } 

响应:

{
  "took": 2,
  "timed_out": false,
  "_shards": { "total": 5, "successful": 5, "skipped": 0, "failed": 0 }, "hits": { "total": 999, "max_score": 0, "hits": [] }, "aggregations": { "group_by_state": { "doc_count_error_upper_bound": 20, "sum_other_doc_count": 770, "buckets": [ { "key": "ID", "doc_count": 27 }, { "key": "TX", "doc_count": 27 }, { "key": "AL", "doc_count": 25 }, { "key": "MD", "doc_count": 25 }, { "key": "TN", "doc_count": 23 }, { "key": "MA", "doc_count": 21 }, { "key": "NC", "doc_count": 21 }, { "key": "ND", "doc_count": 21 }, { "key": "MO", "doc_count": 20 }, { "key": "AK", "doc_count": 19 } ] } } } 

Java实现:

    @Test
    public void test2(){ RestClient lowLevelRestClient = RestClient.builder( new HttpHost("172.16.73.50", 9200, "http")).build(); RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); SearchRequest searchRequest = new SearchRequest("bank"); searchRequest.types("account"); TermsAggregationBuilder aggregation = AggregationBuilders.terms("group_by_state") .field("state.keyword"); SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder(); searchSourceBuilder.aggregation(aggregation); searchSourceBuilder.size(0); searchRequest.source(searchSourceBuilder); try { SearchResponse searchResponse = client.search(searchRequest); Aggregations aggs = searchResponse.getAggregations(); Terms byStateAggs = aggs.get("group_by_state"); Terms.Bucket b = byStateAggs.getBucketByKey("ID"); //只取key是ID的bucket System.out.println(b.getKeyAsString()+","+b.getDocCount()); System.out.println("!!!"); List<? extends Bucket> aggList = byStateAggs.getBuckets();//获取bucket数组里所有数据 for (Bucket bucket : aggList) { System.out.println("key:"+bucket.getKeyAsString()+",docCount:"+bucket.getDocCount());; } } catch (IOException e) { e.printStackTrace(); } } 

Search Scroll API

search scroll API是用于处理search request里面的大量数据的。

• 使用ES做分页查询有两种方法。一是配置search request的from,size参数。二是使用scroll API。搜索结果建议使用scroll API，查询效率高。

为了使用scroll，按照下面给出的步骤执行：

初始化search scroll上下文

带有scroll参数的search请求必须被执行，来初始化scroll session。ES能检测到scroll参数的存在，保证搜索上下文在相应的时间间隔里存活

SearchRequest searchRequest = new SearchRequest("account"); //从 account 索引中查询
SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder();
searchSourceBuilder.query(matchQuery("first", "Virginia")); //match条件 searchSourceBuilder.size(size); //一次取回多少数据 searchRequest.source(searchSourceBuilder); searchRequest.scroll(TimeValue.timeValueMinutes(1L));//设置scroll间隔 SearchResponse searchResponse = client.search(searchRequest); String scrollId = searchResponse.getScrollId(); //取回这条响应的scroll id,在后续的scroll调用中会用到 SearchHit[] hits = searchResponse.getHits().getHits();//得到文档数组 

取回所有相关文档

第二步，得到的scroll id 和新的scroll间隔要设置到 SearchScrollRequest里，再调用searchScroll方法。
ES会返回一批带有新scroll id的查询结果。以此类推，新的scroll id可以用于子查询，来得到另一批新数据。这个过程应该在一个循环内，直到没有数据返回为止,这意味着scroll消耗殆尽，所有匹配上的数据都已经取回。

SearchScrollRequest scrollRequest = new SearchScrollRequest(scrollId);  //传入scroll id并设置间隔。
scrollRequest.scroll(TimeValue.timeValueSeconds(30));
SearchResponse searchScrollResponse = client.searchScroll(scrollRequest);//执行scroll搜索
scrollId = searchScrollResponse.getScrollId();  //得到本次scroll id hits = searchScrollResponse.getHits(); 

清理 scroll 上下文

使用Clear scroll API来检测到最后一个scroll id 来释放scroll上下文.虽然在scroll过期时，这个清理行为会最终自动触发，但是最好的实践是当scroll session结束时，马上释放它。

可选参数

scrollRequest.scroll(TimeValue.timeValueSeconds(60L));  //设置60S的scroll存活时间
scrollRequest.scroll("60s"); //字符串参数

如果在scrollRequest不设置的话，会以searchRequest.scroll()设置的为准。

同步执行

SearchResponse searchResponse = client.searchScroll(scrollRequest);

异步执行

client.searchScrollAsync(scrollRequest, new ActionListener<SearchResponse>() {
    @Override
    public void onResponse(SearchResponse searchResponse) { } @Override public void onFailure(Exception e) { } }); 

• 需要注意的是，search scroll API的请求响应返回值也是一个searchResponse对象。

完整示例

    @Test
    public void test3(){ RestClient lowLevelRestClient = RestClient.builder( new HttpHost("172.16.73.50", 9200, "http")).build(); RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); SearchRequest searchRequest = new SearchRequest("bank"); SearchSourceBuilder searchSourceBuilder = new SearchSourceBuilder(); MatchAllQueryBuilder mqb = QueryBuilders.matchAllQuery(); searchSourceBuilder.query(mqb); searchSourceBuilder.size(10); searchRequest.source(searchSourceBuilder); searchRequest.scroll(TimeValue.timeValueMinutes(1L)); try { SearchResponse searchResponse = client.search(searchRequest); String scrollId = searchResponse.getScrollId(); SearchHit[] hits = searchResponse.getHits().getHits(); System.out.println("first scroll:"); for (SearchHit searchHit : hits) { System.out.println(searchHit.getSourceAsString()); } Scroll scroll = new Scroll(TimeValue.timeValueMinutes(1L)); System.out.println("loop scroll:"); while(hits != null && hits.length>0){ SearchScrollRequest scrollRequest = new SearchScrollRequest(scrollId); scrollRequest.scroll(scroll); searchResponse = client.searchScroll(scrollRequest); scrollId = searchResponse.getScrollId(); hits = searchResponse.getHits().getHits(); for (SearchHit searchHit : hits) { System.out.println(searchHit.getSourceAsString()); } } ClearScrollRequest clearScrollRequest = new ClearScrollRequest(); clearScrollRequest.addScrollId(scrollId); ClearScrollResponse clearScrollResponse = client.clearScroll(clearScrollRequest); boolean succeeded = clearScrollResponse.isSucceeded(); System.out.println("cleared:"+succeeded); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } 

Info API

Info API 提供一些关于集群、节点相关的信息查询。

request

MainResponse response = client.info();

response

ClusterName clusterName = response.getClusterName(); 
String clusterUuid = response.getClusterUuid(); 
String nodeName = response.getNodeName(); 
Version version = response.getVersion(); 
Build build = response.getBuild(); 

    @Test
    public void test4(){ RestClient lowLevelRestClient = RestClient.builder( new HttpHost("172.16.73.50", 9200, "http")).build(); RestHighLevelClient client = new RestHighLevelClient(lowLevelRestClient); try { MainResponse response = client.info(); ClusterName clusterName = response.getClusterName(); String clusterUuid = response.getClusterUuid(); String nodeName = response.getNodeName(); Version version = response.getVersion(); Build build = response.getBuild(); System.out.println("cluster name:"+clusterName); System.out.println("cluster uuid:"+clusterUuid); System.out.println("node name:"+nodeName); System.out.println("node version:"+version); System.out.println("node name:"+nodeName); System.out.println("build info:"+build); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } 

总结

关于Elasticsearch 的 Java High Level REST Client API的基本用法大概就是这些，一些进阶技巧、概念要随时查阅官方文档。