校园选课助手【5】-解决Elasticsearch和MySQL同步

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";//RoutingKeypublic static final String INSERT_KEY = "course.insert";public static final String DELETE_KEY = "course.delete";@Beanpublic TopicExchange topicExchange(){return new TopicExchange(EXCHANGE_NAME,true,false);}@Beanpublic Queue insertQueue(){return new Queue(INSERT_QUEUE_NAME,true);}@Beanpublic Queue deleteQueue(){return new Queue(DELETE_QUEUE_NAME,true);}/*** 绑定队列和交换机关系*/@Beanpublic Binding insertQueueBinding(){return BindingBuilder.bind(insertQueue()).to(topicExchange()).with(INSERT_KEY);}@Beanpublic 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 {@Autowiredprivate ICourseService courseService;@Autowiredprivate RabbitTemplate rabbitTemplate;@PostMappingpublic 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 {@ResourceICourselService 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<CourseMapper, Course> implements ICourseService {@ResourceRestHighLevelClient client;@Overridepublic 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requestIndexRequest request = new IndexRequest("Course").id(CourseDoc.getId().toString());//2.准备DSLrequest.source(JSON.toJSONString(CourseDoc), XContentType.JSON);//3.发送请求client.index(request,RequestOptions.DEFAULT);} catch (IOException e) {throw new RuntimeException(e);}}@Overridepublic void deleteDocById(Long id) {try {//1.准备requestDeleteRequest request = new DeleteRequest("Course",id.toString());//2.发送请求client.delete(request,RequestOptions.DEFAULT);} catch (IOException e) {throw new RuntimeException(e);}}
}