SpringBoot Mapper Bean 創建失敗

***************************
APPLICATION FAILED TO START
***************************
Description:
Field mapper in com.demo.service.impl.UserServiceImpl required a bean of type 'com.demo.mapper.UserMapper' that could not be found.
Action:

Consider defining a bean of type 'com.demo.mapper.UserMapper' in your configuration.

SpringBoot啓動失敗，Bean配置失敗

原因：在mybatis-spring-boot-autoconfigure的jar包中有一個類 MybatisAutoConfiguration，在這個類中的registerBeanDefinitions方法告訴了我們

@Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

      logger.debug("Searching for mappers annotated with @Mapper");

      ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);

      try {
        if (this.resourceLoader != null) {
          scanner.setResourceLoader(this.resourceLoader);
        }

        List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
        if (logger.isDebugEnabled()) {
          for (String pkg : packages) {
            logger.debug("Using auto-configuration base package '{}'", pkg);
          }
        }

        scanner.setAnnotationClass(Mapper.class);
        scanner.registerFilters();
        scanner.doScan(StringUtils.toStringArray(packages));
      } catch (IllegalStateException ex) {
        logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex);
      }
    }

解決方案

1、mapper(Dao層)

添加 @Mapper

2、在啓動類

@MapperScan(value = "com.merveille.dao")