直接上程式碼

package course.service.impl;
 
import course.entity.Course;
import course.entity.CourseDetail;
import course.mapper.CourseDetailMapper;
import course.mapper.CourseMapper;
import course.mapper.StudentMapper;
import course.service.CourseService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Isolation;
import org.springframework.transaction.annotation.Transactional;
 
import java.util.Objects;
 

@Service
public class CourseServiceImpl implements
 
 CourseService {
    private Logger logger = LoggerFactory.getLogger(CourseServiceImpl.class);
 
    @Autowired
    StudentMapper studentMapper;
 
    @Autowired
    CourseMapper courseMapper;
 
    @Autowired
    CourseDetailMapper courseDetailMapper;
 
 
    /**使用for update一定要加上這個事務
     * 當事務處理完後，for update才會將行級鎖解除
 
*/
    @Transactional(isolation = Isolation.READ_COMMITTED)
    // @Transactional(value = "testTransactionManager") //如果是多資料來源，需要制定資料來源
    @Override
    public Object chooseCourse(String studentCode, Integer courseId) {
 
        /** courseMapper.queryAllById(courseId)會對所選中的那條記錄加行級鎖，其他執行緒會在此排隊，當事務提交後，才會進行解鎖*/
        Course course = courseMapper.queryAllById(courseId);
 
        int electiveNum = course.getElectiveNum();
        int totalNum = course.getElectiveTotal();
        logger.info("After Lock Step 1, Thread: {},courseId{}, studentId: {}, electiveNum: {}, total: {}", Thread.currentThread(),courseId,studentCode, electiveNum, totalNum);
 
        if (Objects.isNull(course)){
            return "課程不存在";
        }
        if (electiveNum >= totalNum) {
            return "此課程已被選完";
        }
 
        /**將此此學生的選課資訊儲存到選課詳情裡面*/
        CourseDetail courseDetail = new CourseDetail();
        courseDetail.setCourseId(courseId);
        courseDetail.setStudentCode(studentCode);
        courseDetailMapper.insert(courseDetail);
 
        /**將course表中的electiveNum進行加1操作
         * 使用sql進行累加更加安全，因為使用方法開始查詢的course中的electiveNum,並不一定是資料庫儲存的值*/
        courseMapper.addElectiveNumByCourseId(courseId);
        return "選課成功";
    }
}

主要是Transactional註解的使用@Transactional(isolation = Isolation.READ_COMMITTED)

選擇READ_COMMITTED註解的話，無論條件列上是否有索引，都不會鎖表，只鎖行

Read Uncommited和Read Committed不存在間隙鎖所以不會存在鎖錶行為

具體詳情可參考:
https://blog.csdn.net/zc_ad/article/details/83582614
https://blog.51cto.com/14230003/2427994