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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9 2020-02-28 13:50:26.771 INFO 8720 --- [ main] c.f.n.NationalpolicyApplication : Starting NationalpolicyApplication on DESKTOP-T450s with PID 8720 (D:\biehl\idea\workspace\nationalpolicy2\target\classes started by Aiyufei in D:\biehl\idea\workspace\nationalpolicy2)
10 2020-02-28 13:50:26.777 INFO 8720 --- [ main] c.f.n.NationalpolicyApplication : No active profile set, falling back to default profiles: default
11 2020-02-28 13:50:28.302 INFO 8720 --- [ main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JDBC repositories in DEFAULT mode.
12 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.
13 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.
14 2020-02-28 13:50:29.271 INFO 8720 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
15 2020-02-28 13:50:29.292 INFO 8720 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat]
16 2020-02-28 13:50:29.294 INFO 8720 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.31]
17 2020-02-28 13:50:29.449 INFO 8720 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
18 2020-02-28 13:50:29.449 INFO 8720 --- [ main] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 2428 ms
19 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)}
20 2020-02-28 13:50:29.525 INFO 8720 --- [ main] o.apache.catalina.core.StandardService : Stopping service [Tomcat]
21 2020-02-28 13:50:29.546 INFO 8720 --- [ main] ConditionEvaluationReportLoggingListener :
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23 Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
24 2020-02-28 13:50:29.681 ERROR 8720 --- [ main] o.s.b.d.LoggingFailureAnalysisReporter :
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26 ***************************
27 APPLICATION FAILED TO START
28 ***************************
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30 Description:
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32 Field repoPolicyContentMapper in com.feixian.nationalpolicy.service.impl.RepoPolicyContentServiceImpl required a bean of type 'com.feixian.nationalpolicy.mapper.RepoPolicyContentMapper' that could not be found.
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34 The injection point has the following annotations:
35 - @org.springframework.beans.factory.annotation.Autowired(required=true)
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38 Action:
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40 Consider defining a bean of type 'com.feixian.nationalpolicy.mapper.RepoPolicyContentMapper' in your configuration.
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43 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。