4. 思云App中使用ES API对课程进行查询。贴出实现的代码，要求可以对课程的标题、作者、分类、描述信息进行查询。 springboot

好的，以下是一个使用ES API对思云App中的课程进行查询的示例代码。它可以对课程的标题、作者、分类、描述信息进行查询。

import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.client.RequestOptions;
import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.common.unit.Fuzziness;
import org.elasticsearch.index.query.MultiMatchQueryBuilder;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

@Service
public class CourseService {
    
    @Autowired
    private RestHighLevelClient client;

    // 搜索课程的函数
    public List<Course> searchCourses(String query) throws IOException {
        // 搜索的index
        String index = "courses";

        // 创建查询条件
        MultiMatchQueryBuilder multiMatchQuery = QueryBuilders.multiMatchQuery(query, "title^3", "author^2", "category^2", "description")
                .fuzziness(Fuzziness.AUTO);

        // 创建搜索请求
        SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
        sourceBuilder.query(multiMatchQuery);
        sourceBuilder.from(0);
        sourceBuilder.size(10);
        SearchRequest searchRequest = new SearchRequest(index);
        searchRequest.source(sourceBuilder);

        // 执行搜索
        SearchResponse searchResponse = client.search(searchRequest, RequestOptions.DEFAULT);

        // 处理搜索结果
        SearchHit[] hits = searchResponse.getHits().getHits();
        List<Course> results = new ArrayList<>();
        for (SearchHit hit : hits) {
            Course course = new Course();
            course.setId(hit.getId());
            course.setTitle((String) hit.getSourceAsMap().get("title"));
            course.setAuthor((String) hit.getSourceAsMap().get("author"));
            course.setCategory((String) hit.getSourceAsMap().get("category"));
            course.setDescription((String) hit.getSourceAsMap().get("description"));
            results.add(course);
        }

        return results;
    }
}

你可以将 `query` 参数设置为你想要搜索的关键词，然后调用 `searchCourses` 函数来执行搜索。搜索结果是一个 `Course` 对象列表，每个对象包含课程的 ID、标题、作者、分类和描述信息。