解决：Field xxMapper in xx.service.impl.xxServiceImpl required a bean of type 'xx.mapper.xxMapper'

1、启动 SpringBoot项目报错，使用的是Springboot、Spring、Mybatis连接Mysql数据库，启动SpringBoot项目报错，错误如下所示：

   _____      .__/\      .__
 _/ ____\____ |__)/__  __|__|____    ____
 \   __\/ __ \|  |\  \/  /  \__  \  /    \
  |  | \  ___/|  | >    <|  |/ __ \|   |  \
  |__|  \___  >__|/__/\_ \__(____  /___|  /
            \/          \/       \/     \/

 -- ::26.771  INFO  --- [           main] c.f.n.NationalpolicyApplication          : Starting NationalpolicyApplication on DESKTOP-T450s with PID  (D:\biehl\idea\workspace\nationalpolicy2\target\classes started by Aiyufei in D:\biehl\idea\workspace\nationalpolicy2)
 -- ::26.777  INFO  --- [           main] c.f.n.NationalpolicyApplication          : No active profile set, falling back to default profiles: default
 -- ::28.302  INFO  --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JDBC repositories in DEFAULT mode.
 -- ::28.336  INFO  --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 28ms. Found  JDBC repository interfaces.
 -- ::28.489  WARN  --- [           main] o.m.s.mapper.ClassPathMapperScanner      : No MyBatis mapper was found in '[com.feixian.mapper]' package. Please check your configuration.
 -- ::29.271  INFO  --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s):  (http)
 -- ::29.292  INFO  --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
 -- ::29.294  INFO  --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.]
 -- ::29.449  INFO  --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
 -- ::29.449  INFO  --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in  ms
 -- ::29.521  WARN  --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'repoPolicyContentController': Unsatisfied dependency expressed through field 'repoPolicyContentService'; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'repoPolicyContentServiceImpl': Unsatisfied dependency expressed through field 'repoPolicyContentMapper'; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'com.feixian.nationalpolicy.mapper.RepoPolicyContentMapper' available: expected at least  bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
 -- ::29.525  INFO  --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
 -- ::29.546  INFO  --- [           main] ConditionEvaluationReportLoggingListener : 

 Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
 -- ::29.681 ERROR  --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

 ***************************
 APPLICATION FAILED TO START
 ***************************

 Description:

 Field repoPolicyContentMapper in com.feixian.nationalpolicy.service.impl.RepoPolicyContentServiceImpl required a bean of type 'com.feixian.nationalpolicy.mapper.RepoPolicyContentMapper' that could not be found.

 The injection point has the following annotations:
     - @org.springframework.beans.factory.annotation.Autowired(required=true)

 Action:

 Consider defining a bean of type 'com.feixian.nationalpolicy.mapper.RepoPolicyContentMapper' in your configuration.

 Process finished with exit code 

2. 报错原因，是因为项目未扫描到 mapper 包。

3. 解决该报错的方法，如下所示：

在项目启动类上加注解  @MapperScan("Mapper文件所在的包")，@MapperScan 是扫描mapper类的注解，就不用在每个mapper类上加@MapperScan了。

4、重启工程成功运行。