Java操作ElasticSearch8.2.0索引库(一)

梦里梦外; 2024-03-16 10:06 44阅读 0赞

#### Java操作elasticsearch8.2.0索引库 ####

*  1.倒排索引
 *  2.正向和倒排
 *  3.连接ElasticSearch
 *   *  3.1 导入maven依赖
     *  3.2 Java连接ElasticSearch
 *  4.对索引的增删操作

## 1.倒排索引 ##

倒排索引中有两个非常重要的概念：

*  文档（`Document`）：用来搜索的数据，其中的每一条数据就是一个文档。例如一个网页、一个商品信息
 *  词条（`Term`）：对文档数据或用户搜索数据，利用某种算法分词，得到的具备含义的词语就是词条。例如：我是中国人，就可以分为：我、是、中国人、中国、国人这样的几个词条

## 2.正向和倒排 ##

那么为什么一个叫做正向索引，一个叫做倒排索引呢？

*  **正向索引**是最传统的，根据id索引的方式。但根据词条查询时，必须先逐条获取每个文档，然后判断文档中是否包含所需要的词条，是**根据文档找词条的过程**。
 *  而**倒排索引**则相反，是先找到用户要搜索的词条，根据词条得到保护词条的文档的id，然后根据id获取文档。是**根据词条找文档的过程**。

是不是恰好反过来了？  
那么两者方式的优缺点是什么呢？

**正向索引**：

*  优点：
    
     *  可以给多个字段创建索引
     *  根据索引字段搜索、排序速度非常快
 *  缺点：
    
     *  根据非索引字段，或者索引字段中的部分词条查找时，只能全表扫描。

**倒排索引**：

*  优点：
    
     *  根据词条搜索、模糊搜索时，速度非常快
 *  缺点：
    
     *  只能给词条创建索引，而不是字段
     *  无法根据字段做排序

**创建倒排索引**是对正向索引的一种特殊处理，流程如下：

*  将每一个文档的数据利用算法分词，得到一个个词条
 *  创建表，每行数据包括词条、词条所在文档id、位置等信息
 *  因为词条唯一性，可以给词条创建索引，例如hash表结构索引

## 3.连接ElasticSearch ##

> 因为ElasticSearch8开始就有了登录校验，所以在Java操作时需要登录用户名和密码才能进行操作！

### 3.1 导入maven依赖 ###

<dependency>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-web</artifactId>
           </dependency>
    
           <dependency>
               <groupId>org.springframework.boot</groupId>
               <artifactId>spring-boot-starter-data-elasticsearch</artifactId>
           </dependency>
    
           <dependency>
               <groupId>org.elasticsearch.client</groupId>
               <artifactId>elasticsearch-rest-client</artifactId>
           </dependency>
    
           <dependency>
               <groupId>co.elastic.clients</groupId>
               <artifactId>elasticsearch-java</artifactId>
               <version>8.2.0</version>
           </dependency>
    
           <dependency>
               <groupId>com.fasterxml.jackson.core</groupId>
               <artifactId>jackson-databind</artifactId>
               <version>2.12.3</version>
           </dependency>
    
           <dependency>
               <groupId>jakarta.json</groupId>
               <artifactId>jakarta.json-api</artifactId>
               <version>2.0.1</version>
           </dependency>

### 3.2 Java连接ElasticSearch ###

@BeforeEach
        void setUp() {
        
            final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
            // 用户名和密码
            Credentials creds = new UsernamePasswordCredentials("elastic", "J=9XqTBAk-2GLwd_msUx");
            credentialsProvider.setCredentials(AuthScope.ANY, creds);
            RestClient restClient = RestClient.builder(
                    HttpHost.create("http://192.168.33.136:9200")
            ).setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback() {
        
                @Override
                public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpAsyncClientBuilder) {
        
                    return httpAsyncClientBuilder.setDefaultCredentialsProvider(credentialsProvider);
                }
            }).build();
            RestClientTransport restClientTransport = new RestClientTransport(restClient, new JacksonJsonpMapper());
            elasticsearchClient = new ElasticsearchClient(restClientTransport);
        }

## 4.对索引的增删操作 ##

package cn.itcast.hotel;
    
    import co.elastic.clients.elasticsearch.ElasticsearchClient;
    import co.elastic.clients.elasticsearch.indices.CreateIndexRequest;
    import co.elastic.clients.json.jackson.JacksonJsonpMapper;
    import co.elastic.clients.transport.rest_client.RestClientTransport;
    import org.apache.http.HttpHost;
    import org.apache.http.auth.AuthScope;
    import org.apache.http.auth.Credentials;
    import org.apache.http.auth.UsernamePasswordCredentials;
    import org.apache.http.client.CredentialsProvider;
    import org.apache.http.impl.client.BasicCredentialsProvider;
    import org.apache.http.impl.nio.client.HttpAsyncClientBuilder;
    import org.elasticsearch.client.RestClient;
    import org.elasticsearch.client.RestClientBuilder;
    import org.junit.jupiter.api.BeforeEach;
    import org.junit.jupiter.api.Test;
    import org.springframework.util.ResourceUtils;
    
    import java.io.File;
    import java.io.FileReader;
    import java.io.IOException;
    
    /**
     * @author 尹稳健~
     * @version 1.0
     * @time 2023/5/28
     */
    public class HotelIndexTest {
        
        private ElasticsearchClient elasticsearchClient;
    
        @Test
        void initialization() {
        
            System.out.println(elasticsearchClient);
        }
    
        //  J=9XqTBAk-2GLwd_msUx
        @Test
        void createIndexRequest() throws IOException {
        
            if (!elasticsearchClient.indices().exists(request -> request.index("hotel")).value()){
        
                File file = ResourceUtils.getFile("classpath:hotel.json");
                FileReader fileReader = new FileReader(file);
                CreateIndexRequest request = CreateIndexRequest.of(
                        builder -> builder.index("hotel")
                                .withJson(fileReader)
                );
                elasticsearchClient.indices().create(request);
            }
    
        }
    
        @Test
        void deleteIndexRequest() throws IOException {
        
            elasticsearchClient.indices().delete(request -> request.index("hotel"));
        }
    
        @BeforeEach
        void setUp() {
        
            final CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
            Credentials creds = new UsernamePasswordCredentials("elastic", "J=9XqTBAk-2GLwd_msUx");
            credentialsProvider.setCredentials(AuthScope.ANY, creds);
            RestClient restClient = RestClient.builder(
                    HttpHost.create("http://192.168.33.136:9200")
            ).setHttpClientConfigCallback(new RestClientBuilder.HttpClientConfigCallback(){
        
                @Override
                public HttpAsyncClientBuilder customizeHttpClient(HttpAsyncClientBuilder httpAsyncClientBuilder) {
        
                    return httpAsyncClientBuilder.setDefaultCredentialsProvider(credentialsProvider);
                }
            }).build();
            RestClientTransport restClientTransport = new RestClientTransport(restClient, new JacksonJsonpMapper());
            elasticsearchClient = new ElasticsearchClient(restClientTransport);
        }
    
    }