spring+mybatis项目中，@Mapper,@Mapper,mybatis.mapper-locations的区别？

Question

springboot+mybatis项目，有如下报错：

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.example.baseproject.mapper.UserMapper.selectByPrimaryKey
    at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:235) ~[mybatis-3.5.11.jar:3.5.11]
    at org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:53) ~[mybatis-3.5.11.jar:3.5.11]
    at org.apache.ibatis.binding.MapperProxy.lambda$cachedInvoker$0(MapperProxy.java:108) ~[mybatis-3.5.11.jar:3.5.11]
    at java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1660) ~[na:1.8.0_351]
    at org.apache.ibatis.util.MapUtil.computeIfAbsent(MapUtil.java:35) ~[mybatis-3.5.11.jar:3.5.11]
    at org.apache.ibatis.binding.MapperProxy.cachedInvoker(MapperProxy.java:95) ~[mybatis-3.5.11.jar:3.5.11]
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:86) ~[mybatis-3.5.11.jar:3.5.11]
    at com.sun.proxy.$Proxy62.selectByPrimaryKey(Unknown Source) ~[na:na]
    at com.example.baseproject.controller.UserController.getUser(UserController.java:18) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_351]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_351]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_351]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_351]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.26.jar:5.3.26]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1072) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:502) ~[tomcat-embed-core-9.0.73.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.26.jar:5.3.26]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:596) ~[tomcat-embed-core-9.0.73.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:209) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.26.jar:5.3.26]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.26.jar:5.3.26]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.26.jar:5.3.26]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.26.jar:5.3.26]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.26.jar:5.3.26]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.26.jar:5.3.26]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:178) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:153) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:492) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:130) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:389) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:926) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1791) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.73.jar:9.0.73]
    at java.lang.Thread.run(Thread.java:750) [na:1.8.0_351]

经测试，如果在mapper接口上使用@Mapper或者在启动类上使用注解@MapperScan都会有这个报错，只有当在application.properties中添加

mybatis.mapper-locations=classpath:mapper/*.xml 

后，程序正常运行。可问题是前面2个注解的功能和properties文件里的参数的功能不是一样的吗？都是指定mapper接口的位置，可为什么一个报错，一个不会报错?

package com.example.baseproject.mapper;

import com.example.baseproject.entity.User;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface UserMapper {
    int deleteByPrimaryKey(Integer id);

    int insert(User record);

    User selectByPrimaryKey(Integer id);

    List<User> selectAll();

    int updateByPrimaryKey(User record);
}

@SpringBootApplication
@MapperScan("com.example.baseproject.mapper")
public class BaseProjectApplication {

    public static void main(String[] args) {
        SpringApplication.run(BaseProjectApplication.class, args);
    }

}

Answer 1

你理解错了，@Mapper和@MapperScan是为了扫描出Mapper接口生成代理对象，而配置文件中配的是xml文件所在路径。