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概念

全文搜索（检索），工作原理：计算机索引程序，扫描文章中的每一个词，对每一个词建立一个索引，指明出现次数和位置。查询时通过索引进行查找，类似于查字典。
因为是通过索引在查，速度较于通过sql查，会快很多。
具体过程如下：
1、建文本库
2、建立索引
3、执行搜索
4、过滤结果

全文搜索相关技术

Lucene：https://lucene.apache.org/core/
Solr：https://solr.apache.org/
Elasticsearch：https://www.elastic.co/cn/elasticsearch
Lucene是搜索引擎，Elasticsearch和Solr都是基于Lucene之上实现的全文检索系统
Elasticsearch和Solr对比，版本比较老，做参考即可

Elasticsearch

概念

一个高度可扩展的开源全文搜索和分析引擎，它允许用户快速地、近实时地对大数据进行存储、搜索和分析，它通常用来支撑有复杂的数据搜索需求的企业级应用 。

近实时

近实时，而不是实时
索引文档到可搜索的时间有一个轻微的延迟（通常为1秒）。之所以会有这个延时，主要考虑查询的性能优化。
想要实时，就得刷新，要么是牺牲索引的效率（每次索引之后刷新），要么就是牺牲查询的效率（每次查询之前都进行刷新 ），Elasticsearch取了折中，每隔n秒自动刷新
Elasticsearch 索引新文档后，不会直接写入磁盘，而是首先存入文件系统缓存，之后根据刷新设置，定期同步到磁盘。索引我们改完内容不会立即被搜索出来，但是会在1秒内可见

索引

相似文档的集合

类型

对一个索引中包含的文档进一步细分

文档

索引的基本单位，与索引中的一个类型相对应

分片(Shard)和副本(Replica)

数据量较大时，把索引分成多个分片来存储索引的部分数据，提高性能/吞吐量
为了安全，一个分片中的数据至少有一个副本

下载

https://www.elastic.co/cn/downloads/elasticsearch
注意版本，spring-boot2.x，不要用最新版本，用7.x.x

启用

命令行进入bin目录，执行elasticsearch启动服务，Ctrl/command + C停止服务
启用localhost:9200，测试Elasticsearch节点是否正在运行，可能会遇到安全认证问题，见问题部分

{"name": "zhangxingxingdeMacBook-Pro.local","cluster_name": "elasticsearch","cluster_uuid": "DwgXhzhwQ9WS0drElcEZmg","version": {"number": "7.11.1", // 当前elasticsearch版本"build_flavor": "default","build_type": "tar","build_hash": "ff17057114c2199c9c1bbecc727003a907c0db7a","build_date": "2021-02-15T13:44:09.394032Z","build_snapshot": false,"lucene_version": "8.7.0", //lucene版本"minimum_wire_compatibility_version": "6.8.0","minimum_index_compatibility_version": "6.0.0-beta1"},"tagline": "You Know, for Search"
}

SpringBoot整合

引入依赖

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-elasticsearch</artifactId>
</dependency>

创建文档类

@Document(indexName = "blog")
@Table(name = "article")
public class EsBlog implements Serializable {private static final long serialVersionUID = 1L;@Id // 主键private String id;private String title;private  String author;private String content;protected EsBlog(){}public EsBlog(String title, String author, String content){this.title = title;this.author = author;this.content = content;}......@Overridepublic String toString(){return String.format("Article[id=%s, title='%s', author='%s', content='%s']",id, title, author, content);}
}

创建资源库

@Repository
public interface EsBlogRepository extends ElasticsearchRepository<EsBlog, String> {Page<EsBlog> findByTitleContainingOrAuthorContainingOrContentContaining(String title, String author, String content, Pageable pageable);
}

注意在创建启动类中进行包扫描，否则注入的时候找不到bean

@EnableJpaRepositories(basePackages = "com.xxx.xxx")

测试文件初始化数据

@RunWith(SpringRunner.class)
@SpringBootTest(classes= SpringApplicationSock.class) // 启动sping-boot，引入IOC
public class EsBlogRepositoryTest {@Autowiredprivate EsBlogRepository esBlogRepository;@Beforepublic void initRepositoryData(){// 清除所有数据esBlogRepository.deleteAll();// 初始化数据,存入es存储库esBlogRepository.save(new EsBlog("静夜思", "李白", "床前明月光，疑是地上霜。举头望明月，低头思故乡。"));esBlogRepository.save(new EsBlog("咏柳", "贺知章", "碧玉妆成一树高，万条垂下绿丝绦。不知细叶谁裁出，二月春风似剪刀。"));esBlogRepository.save(new EsBlog("悯农", "李绅", "锄禾日当午，汗滴禾下土。谁知盘中餐，粒粒皆辛苦。"));}@Testpublic void testFindDistincEsBlogTitleContainingOrSummaryContainingOrContentContaining(){// 初始化一个分页请求Pageable pageable = PageRequest.of(0, 20);String title = "咏";String author = "王";String content = "月";Page<EsBlog> page = esBlogRepository.findByTitleContainingOrAuthorContainingOrContentContaining(title, author, content, pageable);System.out.println("=================start");for(EsBlog blog : page){System.out.println(blog.toString());}System.out.println("=================end");}
}

查看存储库
http://localhost:9200/_cat/indices?v=

上述内容通过查询条件，只能查出两条数据

查看blog相关信息
http://localhost:9200/blog

{"blog": {"aliases": {},"mappings": {"properties": {"_class": {"type": "keyword","index": false,"doc_values": false},"author": {"type": "text","fields": {"keyword": {"type": "keyword","ignore_above": 256}}},"content": {"type": "text","fields": {"keyword": {"type": "keyword","ignore_above": 256}}},"title": {"type": "text","fields": {"keyword": {"type": "keyword","ignore_above": 256}}}}},"settings": {"index": {"routing": {"allocation": {"include": {"_tier_preference": "data_content"}}},"refresh_interval": "1s","number_of_shards": "1","provided_name": "blog","creation_date": "1703233943853","store": {"type": "fs"},"number_of_replicas": "1","uuid": "0ELJkqnmTg-tDwritULELA","version": {"created": "7110199"}}}}
}

创建控制器

@RestController
@RequestMapping("/blogs")
public class EsBlogController {@Autowiredprivate EsBlogRepository esBlogRepository;@GetMappingpublic List<EsBlog> list(@RequestParam(value = "title", required = false, defaultValue = "") String title,@RequestParam(value = "author", required = false, defaultValue = "") String author,@RequestParam(value = "content", required = false, defaultValue = "") String content,@RequestParam(value = "pageIndex", required = false, defaultValue = "0") int pageIndex,@RequestParam(value = "pageSize", required = false, defaultValue = "10") int pageSize){Pageable pageable = PageRequest.of(pageIndex, pageSize);Page<EsBlog> page = esBlogRepository.findByTitleContainingOrAuthorContainingOrContentContaining(title, author, content, pageable);return page.getContent();}
}

问题

1、ElasticSearch服务正常启动，但是在浏览器上无法访问http://localhost:9200，最新版本可能会有这个问题
received plaintext http traffic on an https channel, closing connection Netty4HttpChannel{localAddress=/[0:0:0:0:0:0:0:1]:9200, remoteAddress=/[0:0:0:0:0:0:0:1]:63470}
解决方法：
ElasticSearch默认开启了安全认证，需要将安全认证关掉
config/elasticsearch.yml，将下面两处的true改为false

2、启动test，提示Unsatisfied dependency expressed through field ‘esBlogRepository’;
未启动spring boot，没有IOC
https://blog.csdn.net/weixin_43801567/article/details/96643032
3、Unable to parse response body for Response{requestLine=POST /blog/_doc?timeout=1m HTTP/1.1, host=http://localhost:9200, response=HTTP/1.1 201 Created}
es服务器的响应程序解析不了，有可能是spring-boot版本低了
spring-boot 2.7.3，es:8.11.3 会有问题，将es改为7.11.1正常

参考

https://blog.csdn.net/weixin_38201936/article/details/121746906
https://blog.csdn.net/qq_50652600/article/details/125521823