RestHighLevelClient查询ES中数据的API主要有：get、multiGet、search、multiSearch、searchScroll，每个方法还有异步查询的操作方法。下面我们就逐个看看这些API的应用。
链接ES构建客户端：
public class EsRestClient {
private String IP;
private int PORT;
private String index;
private String type;
RestHighLevelClient client;
@Before
public void init() {
this.IP = "192.168.5.166";
this.PORT = 9200;
this.index = "index3";
this.type = "user1";
client = new RestHighLevelClient(
RestClient.builder(
new HttpHost(IP, PORT, "http")));
}
}get方法查询：
public final GetResponse get(GetRequest getRequest, Header... headers) throws IOException {
return (GetResponse)this.performRequestAndParseEntity(getRequest, Request::get, GetResponse::fromXContent, Collections.singleton(404), headers);
}查询ES：
@Test
public void test1() throws IOException {
GetRequest getRequest = new GetRequest(index);
getRequest.id("1");
String[] includes = new String[]{"*", "birthday"};
String[] excludes = Strings.EMPTY_ARRAY;
FetchSourceContext fetchSourceContext = new FetchSourceContext(true, includes, excludes);
getRequest.fetchSourceContext(fetchSourceContext);
GetResponse response = client.get(getRequest);
System.out.println(response.getSource().keySet().toString());
}输出结果：
get方法查询es接收的参数为GetRequest，我们先要构建GetRequest对象才可以对ES进行查询
public class GetRequest extends SingleShardRequest<GetRequest> implements RealtimeRequest {
private String type;
private String id;
private String routing;
private String parent;
private String preference;
private String[] storedFields;
private FetchSourceContext fetchSourceContext;
private boolean refresh = false;
boolean realtime = true;
private VersionType versionType;
private long version;
......
...
...
}在GetRequest对象中设置我们要查询的es索引（index）、类型（type）、 id、路由、分片、版本 等信息，也可以指定展示我们要查询的特定的列或排除的列信息FetchSourceContext。get查询是根据ID进行精确匹配的插叙，查询的参数封装在GetRequest中。
multiGet查询：
public final MultiGetResponse multiGet(MultiGetRequest multiGetRequest, Header... headers) throws IOException {
return (MultiGetResponse)this.performRequestAndParseEntity(multiGetRequest, Request::multiGet, MultiGetResponse::fromXContent, Collections.singleton(404), headers);
}一次查询多个ID数据：
@Test
public void test2() throws IOException {
String[] includes = new String[]{"*", "birthday"};
String[] excludes = Strings.EMPTY_ARRAY;
FetchSourceContext fetchSourceContext = new FetchSourceContext(true, includes, excludes);
MultiGetRequest multiGetRequest = new MultiGetRequest();
multiGetRequest.add(new MultiGetRequest.Item(index,type,"1").fetchSourceContext(fetchSourceContext)); //通过Item添加查询条件
multiGetRequest.add(index,type,"2"); //直接添加查询条件
MultiGetResponse multiGetItemResponses = client.multiGet(multiGetRequest);
MultiGetItemResponse[] responses = multiGetItemResponses.getResponses();
for(MultiGetItemResponse response : responses){
System.out.println(response.getResponse().getSource().keySet().toString());
}
}输出结果：
MultiGetRequest类内还定义了一个内部类Item，查询条件都封装在Item中。上面我们添加了两个查询条件，一个是通过Item内部类的构造函数添加，另一个是调用MultiGetRequest的add方法添加，其实都是创建一个新的Item对象。下面是add方法添加查询条件的源码：
public MultiGetRequest add(String index, @Nullable String type, String id) {
this.items.add(new MultiGetRequest.Item(index, type, id));
return this;
}
search查询：
get查询我们只能根据ID进行精确查询，而search查询，我们可以自定义查询字段进行查询。
public final SearchResponse search(SearchRequest searchRequest, Header... headers) throws IOException {
return (SearchResponse)this.performRequestAndParseEntity(searchRequest, Request::search, SearchResponse::fromXContent, Collections.emptySet(), headers);
}查询：
@Test
public void test3() {
SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
sourceBuilder.from(0);
sourceBuilder.size(10);
sourceBuilder.fetchSource(new String[]{"*"}, Strings.EMPTY_ARRAY);
MatchQueryBuilder matchQueryBuilder = QueryBuilders.matchQuery("name", "rabbit");
MultiMatchQueryBuilder multiMatchQueryBuilder = QueryBuilders.multiMatchQuery("YunZhiHui", "address", "company");
TermQueryBuilder termQueryBuilder = QueryBuilders.termQuery("interest", "game steak");
RangeQueryBuilder rangeQueryBuilder = QueryBuilders.rangeQuery("birthday");
rangeQueryBuilder.gte("2018-01-26");
rangeQueryBuilder.lte("2019-01-26");
BoolQueryBuilder boolBuilder = QueryBuilders.boolQuery();
boolBuilder.must(matchQueryBuilder);
boolBuilder.must(termQueryBuilder);
boolBuilder.must(rangeQueryBuilder);
boolBuilder.should(multiMatchQueryBuilder);
sourceBuilder.query(boolBuilder);
SearchRequest searchRequest = new SearchRequest(index);
searchRequest.types(type);
searchRequest.source(sourceBuilder);
try {
SearchResponse response = client.search(searchRequest);
System.out.println(response);
} catch (IOException e) {
e.printStackTrace();
}
}search查询的主要参数是SearchRequest，我们的查询条件index、type、字段、字段值 都封装在SearchRequest中；而index、type是直接封装在SearchRequest的对象中，查询的字段、字段值、查询方式则封装在SearchRequest中的对象属性SearchSourceBuilder中。
下面是SearchRequest的部分属性：
public final class SearchRequest extends ActionRequest implements Replaceable {
private SearchType searchType;
private String[] indices;
@Nullable
private String routing;
@Nullable
private String preference;
private SearchSourceBuilder source; //封装查询条件
private Boolean requestCache;
private Scroll scroll;
private int batchedReduceSize;
private int maxConcurrentShardRequests;
private int preFilterShardSize;
private String[] types;
private IndicesOptions indicesOptions;
......
......从上面的test3中可以看出，要想构建出SearchSourceBuilder，还需要两个类：BoolQueryBuilder、QueryBuilders。BoolQueryBuilder用于构建bool查询的查询条件，也是在实际应用中使用较多的查询。QueryBuilder用于构建match、term、multiMatch等查询。如果我们的查询条件很简单，只需要match、term、multiMatch也可以不适用BoolQueryBuilder，而直接使用QueryBuilders构建出来的QueryBuilder对象。
