未优化前：课程检索库中的数据经过一次同步后固定不变，用户搜索到对应的课程后点击跳转到课程详情页面，进行选课

存在的问题：

1. 用户使用不友好，搜索就是为了进行选课，应该返回对应课程的余量，如果没有余量了，进行友好提示，如果有余量，跳转到详情页面进行选课。
2. 数据不一致，可能修改了课程信息，而检索库中的数据依旧没有更新。

解决方案：
引入消息队列，当CourseController将数据写入mysql后，需要自己再往MQ发条消息，说"数据更新了"，EsController收到消息去更新索引库。

1.声明队列和交换机

@Configuration public class MqConfig { 	//交换机名称     public static final String EXCHANGE_NAME = "course.topic";     //新增和修改队列     public static final String INSERT_QUEUE_NAME = "course.insert.queue";     //删除队列     public static final String DELETE_QUEUE_NAME = "course.delete.queue";     //RoutingKey     public static final String INSERT_KEY = "course.insert";     public static final String DELETE_KEY = "course.delete";      @Bean     public TopicExchange topicExchange(){         return new TopicExchange(EXCHANGE_NAME,true,false);     }      @Bean     public Queue insertQueue(){         return new Queue(INSERT_QUEUE_NAME,true);     }      @Bean     public Queue deleteQueue(){         return new Queue(DELETE_QUEUE_NAME,true);     }      /**      * 绑定队列和交换机关系      */     @Bean     public Binding insertQueueBinding(){         return BindingBuilder                 .bind(insertQueue())                 .to(topicExchange())                 .with(INSERT_KEY);     }      @Bean     public Binding deleteQueueBinding(){         return BindingBuilder                 .bind(deleteQueue())                 .to(topicExchange())                 .with(DELETE_KEY);     }  

2.发送消息

import org.springframework.amqp.rabbit.core.RabbitTemplate; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*;  import java.security.InvalidParameterException;  @RestController @RequestMapping("Course") public class courseController {      @Autowired     private ICourseService courseService;      @Autowired     private RabbitTemplate rabbitTemplate;      @PostMapping     public void saveCourse(@RequestBody Course course){         courseService.save(course);         rabbitTemplate.convertAndSend("course.topic","course.insert", course.getId());     }      @PutMapping()     public void updateById(@RequestBody course course){         if (course.getId() == null) {             throw new InvalidParameterException("id不能为空");         }         courseService.updateById(course);          // 发送MQ消息         rabbitTemplate.convertAndSend("course.topic","course.insert", course.getId());     }      @DeleteMapping("/{id}")     public void deleteById(@PathVariable("id") Long id) {         courseService.removeById(id);          // 发送MQ消息         rabbitTemplate.convertAndSend("course.topic", "course.delete", id);     }    }  

3.监听消息队列并进行处理

 import org.springframework.amqp.rabbit.annotation.RabbitListener; import org.springframework.stereotype.Component;  import javax.annotation.Resource;   @Component public class CourseListener {      @Resource     ICourselService courseService;      /**      * 监听课程新增或者修改的业务      * id接受一个Long，因为发送过来的是一个Long id      */     @RabbitListener(queues = "course.insert.queue“)     public void listenCourseInsertAndUpdate(Long id){         CourseService.insertDocById(id);     }      /**      * 监听课程删除业务      */     @RabbitListener(queues = "course.delete.queue“)     public void listenCourseDelete(Long id){         CourseService.deleteDocById(id);     } }  

4.实现上述service功能

新增或修改课程逻辑

• 1）根据id查询课程数据Item
• 2）将Item封装为ItemDoc
• 3）将ItemDoc序列化为JSON
• 4）创建IndexRequest，指定索引库名和id
• 5）准备请求参数，也就是JSON文档
• 6）发送请求

删除课程逻辑

• 1）准备Request对象，因为是删除，这次是DeleteRequest对象。要指定索引库名和id
• 3）发送请求。因为是删除，所以是client.delete()方法

import org.springframework.stereotype.Service;  import javax.annotation.Resource; import java.io.IOException;  @Service public class CourseService extends ServiceImpl implements ICourseService {      @Resource     RestHighLevelClient client;      @Override     public void insertDocById(Long id) {         try {             //0.根据ID查数据，并转为文档类型             Course Course = getById(id);             CourseDoc CourseDoc = new CourseDoc(Course);             //1.准备request             IndexRequest request = new IndexRequest("Course").id(CourseDoc.getId().toString());             //2.准备DSL             request.source(JSON.toJSONString(CourseDoc), XContentType.JSON);             //3.发送请求             client.index(request,RequestOptions.DEFAULT);         } catch (IOException e) {             throw new RuntimeException(e);         }     }      @Override     public void deleteDocById(Long id) {          try {             //1.准备request             DeleteRequest request = new DeleteRequest("Course",id.toString());             //2.发送请求             client.delete(request,RequestOptions.DEFAULT);         } catch (IOException e) {             throw new RuntimeException(e);         }      } }