1. 初识Elasticsearch

一个分布式的、Restful风格的搜索引擎。
支持对各种类型的数据的检索。
搜索速度快，可以提供实时的搜索服务。
便于水平扩展，每秒可以处理PB级海量数据

Elasticsearch术语：?

索引、类型、文档、字段。
集群、节点、分片、副本。

Elasticsearch与数据库的对比：??

Elasticsearch	数据库
索引	database
类型	table
文档	一行数据
字段	一列数据

Elasticsearch6.0后变更：

Elasticsearch	数据库
索引	database
类型	逐渐废弃
文档	一行数据
字段	一列数据

其他数据：

集群：多个Elasticsearch组成一个集群
节点：集群中每个Elasticsearch为一个节点
分片：一个索引在存储时可以分为多个分片
副本：是对分片的复制，一个分片有多个副本。提高可用性

2. Spring整合Elasticsearch：?

2.1 引入依赖：

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

2.2 配置：

  data:
    elasticsearch:
      cluster-name: nowcoder
      cluster-nodes: 127.0.0.1:9300

2.3 解决冲突：

elasticsearch和Redis的底层都是基于netty实现，两者在启动时会有冲突。

CommunityApplication?

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import javax.annotation.PostConstruct;

@SpringBootApplication
@MapperScan("com.nowcoder.community.mapper")
public class CommunityApplication {

    @PostConstruct
    public void init() {
        // 解决netty启动冲突问题
        // see Netty4Utils.setAvailableProcessors()
        System.setProperty("es.set.netty.runtime.available.processors", "false");
    }

    public static void main(String[] args) {
        SpringApplication.run(CommunityApplication.class, args);
    }

}

2.4 将帖子的实体类存入Elasticsearch,创建索引

import org.springframework.data.annotation.Id;
import org.springframework.data.elasticsearch.annotations.Document;
import org.springframework.data.elasticsearch.annotations.Field;
import org.springframework.data.elasticsearch.annotations.FieldType;

import java.util.Date;

@Document(indexName = "discusspost",type = "_doc",shards = 6,replicas = 3)
public class DiscussPost {

    @Id
    private int id;

    @Field(type = FieldType.Integer)
    private int userId;

    @Field(type = FieldType.Text,analyzer = "ik_max_word",searchAnalyzer = "ik_smart")
    private String title;

    @Field(type = FieldType.Text,analyzer = "ik_max_word",searchAnalyzer = "ik_smart")
    private String content;

    @Field(type = FieldType.Integer)
    private int type;

    @Field(type = FieldType.Integer)
    private int status;

    @Field(type = FieldType.Date)
    private Date createTime;

    @Field(type = FieldType.Integer)
    private int commentCount;

    @Field(type = FieldType.Double)
    private double score;

2.5 创建接口 ElasticsearchRepository

import com.nowcoder.community.entity.DiscussPost;
import org.springframework.data.elasticsearch.repository.ElasticsearchRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface DiscussPostRepository extends ElasticsearchRepository<DiscussPost, Integer> {

}

2.6 测试

import com.nowcoder.community.elasticsearch.DiscussPostRepository;
import com.nowcoder.community.entity.DiscussPost;
import com.nowcoder.community.mapper.DiscussPostMapper;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.SearchHits;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilder;
import org.elasticsearch.search.fetch.subphase.highlight.HighlightField;
import org.elasticsearch.search.sort.SortBuilders;
import org.elasticsearch.search.sort.SortOrder;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.elasticsearch.core.ElasticsearchTemplate;
import org.springframework.data.elasticsearch.core.SearchResultMapper;
import org.springframework.data.elasticsearch.core.aggregation.AggregatedPage;
import org.springframework.data.elasticsearch.core.aggregation.impl.AggregatedPageImpl;
import org.springframework.data.elasticsearch.core.query.NativeSearchQueryBuilder;
import org.springframework.data.elasticsearch.core.query.SearchQuery;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
@ContextConfiguration(classes = CommunityApplication.class)
public class ElasticSearchTests {

    @Autowired
    private DiscussPostMapper discussPostMapper;

    @Autowired
    private DiscussPostRepository discussPostRepository;

    @Autowired
    private ElasticsearchTemplate elasticsearchTemplate;

    @Test
    public void testInsert(){
        discussPostRepository.save(discussPostMapper.selectDiscussPostById(241));
        discussPostRepository.save(discussPostMapper.selectDiscussPostById(242));
        discussPostRepository.save(discussPostMapper.selectDiscussPostById(243));
    }

    @Test
    public void testInsertList(){
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(101,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(102,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(103,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(111,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(112,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(131,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(132,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(133,0,100));
        discussPostRepository.saveAll(discussPostMapper.selectDiscussPosts(134,0,100));
    }

    @Test
    public void testUpdate(){
        DiscussPost post = discussPostMapper.selectDiscussPostById(231);
        post.setContent("我是新人，使劲灌水");
        discussPostRepository.save(post);
    }

    @Test
    public void testDelete(){
        //discussPostRepository.delete(discussPostMapper.selectDiscussPostById(231));
        discussPostRepository.deleteAll();
    }

    @Test
    public void testSearchByRepository() {
        SearchQuery searchQuery = new NativeSearchQueryBuilder()
                .withQuery(QueryBuilders.multiMatchQuery("互联网寒冬", "title", "content"))
                .withSort(SortBuilders.fieldSort("type").order(SortOrder.DESC))
                .withSort(SortBuilders.fieldSort("score").order(SortOrder.DESC))
                .withSort(SortBuilders.fieldSort("createTime").order(SortOrder.DESC))
                .withPageable(PageRequest.of(0, 10))
                .withHighlightFields(
                        new HighlightBuilder.Field("title").preTags("<em>").postTags("</em>"),
                        new HighlightBuilder.Field("content").preTags("<em>").postTags("</em>")
                ).build();

        // elasticTemplate.queryForPage(searchQuery, class, SearchResultMapper)
        // 底层获取得到了高亮显示的值, 但是没有返回.

        Page<DiscussPost> page = discussPostRepository.search(searchQuery);
        System.out.println(page.getTotalElements());
        System.out.println(page.getTotalPages());
        System.out.println(page.getNumber());
        System.out.println(page.getSize());
        for (DiscussPost post : page) {
            System.out.println(post);
        }
    }

    @Test
    public void testSearchByTemplate(){
        SearchQuery searchQuery = new NativeSearchQueryBuilder()
                .withQuery(QueryBuilders.multiMatchQuery("互联网寒冬", "title", "content"))
                .withSort(SortBuilders.fieldSort("type").order(SortOrder.DESC))
                .withSort(SortBuilders.fieldSort("score").order(SortOrder.DESC))
                .withSort(SortBuilders.fieldSort("createTime").order(SortOrder.DESC))
                .withPageable(PageRequest.of(0, 10))
                .withHighlightFields(
                        new HighlightBuilder.Field("title").preTags("<em>").postTags("</em>"),
                        new HighlightBuilder.Field("content").preTags("<em>").postTags("</em>")
                ).build();

        Page<DiscussPost> page=elasticsearchTemplate.queryForPage(searchQuery, DiscussPost.class, new SearchResultMapper() {
            @Override
            public <T> AggregatedPage<T> mapResults(SearchResponse response, Class<T> aClass, Pageable pageable) {
                SearchHits hits=response.getHits();
                if (hits.getTotalHits()<=0){
                    return null;
                }

                List<DiscussPost> list=new ArrayList<>();
                for (SearchHit hit : hits) {
                    DiscussPost post = new DiscussPost();

                    String id = hit.getSourceAsMap().get("id").toString();
                    post.setId(Integer.valueOf(id));

                    String userId = hit.getSourceAsMap().get("userId").toString();
                    post.setUserId(Integer.valueOf(userId));

                    String title = hit.getSourceAsMap().get("title").toString();
                    post.setTitle(title);

                    String content = hit.getSourceAsMap().get("content").toString();
                    post.setContent(content);

                    String status = hit.getSourceAsMap().get("status").toString();
                    post.setStatus(Integer.valueOf(status));

                    String createTime = hit.getSourceAsMap().get("createTime").toString();
                    post.setCreateTime(new Date(Long.valueOf(createTime)));

                    String commentCount = hit.getSourceAsMap().get("commentCount").toString();
                    post.setCommentCount(Integer.valueOf(commentCount));

                    //处理高亮显示的结果
                    HighlightField tileField = hit.getHighlightFields().get("title");
                    if (tileField!=null){
                        post.setTitle(tileField.getFragments()[0].toString());
                    }

                    HighlightField contentField = hit.getHighlightFields().get("content");
                    if (contentField != null) {
                        post.setContent(contentField.getFragments()[0].toString());
                    }

                    list.add(post);
                }

                return new AggregatedPageImpl(list,pageable,
                        hits.getTotalHits(),response.getAggregations(),response.getScrollId(),hits.getMaxScore());
            }
        });

        System.out.println(page.getTotalElements());
        System.out.println(page.getTotalPages());
        System.out.println(page.getNumber());
        System.out.println(page.getSize());
        for (DiscussPost post : page) {
            System.out.println(post);
        }
    }
}