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：

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_/ ____\____ |__)/__  __|__|____    ____
   __/ __ |  |  /  /  \__    /    
 |  |   ___/|  | >    <|  |/ __ |   |  
 |__|  \___  >__|/__/\_ \__(____  /___|  /
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2020-02-28 13:50:26.771  INFO 8720 --- [           main] c.f.n.NationalpolicyApplication          : Starting NationalpolicyApplication on DESKTOP-T450s with PID 8720 (D:iehlideaworkspace
ationalpolicy2	argetclasses started by Aiyufei in D:iehlideaworkspace
ationalpolicy2)
2020-02-28 13:50:26.777  INFO 8720 --- [           main] c.f.n.NationalpolicyApplication          : No active profile set, falling back to default profiles: default
2020-02-28 13:50:28.302  INFO 8720 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JDBC repositories in DEFAULT mode.
2020-02-28 13:50:28.336  INFO 8720 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 28ms. Found 0 JDBC repository interfaces.
2020-02-28 13:50:28.489  WARN 8720 --- [           main] o.m.s.mapper.ClassPathMapperScanner      : No MyBatis mapper was found in '[com.feixian.mapper]' package. Please check your configuration.
2020-02-28 13:50:29.271  INFO 8720 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-02-28 13:50:29.292  INFO 8720 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-02-28 13:50:29.294  INFO 8720 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.31]
2020-02-28 13:50:29.449  INFO 8720 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-02-28 13:50:29.449  INFO 8720 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 2428 ms
2020-02-28 13:50:29.521  WARN 8720 --- [           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 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
2020-02-28 13:50:29.525  INFO 8720 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2020-02-28 13:50:29.546  INFO 8720 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-02-28 13:50:29.681 ERROR 8720 --- [           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 1

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。