果然不看教程直接使用在遇到问题会懵逼，连解决问题都得搜半天还不一定能帮你解决了。。。
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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启动失败，告诉我Bean配置失败，楼主看了看 该用的注解都用上了 这是咋的回事嘞？
mapper(Dao层)
1 package com.demo.mapper; 2 3 import org.springframework.context.annotation.ComponentScan; 4 import org.springframework.stereotype.Repository; 5 6 import com.demo.domain.User; 7 8 //@Component 9 @Repository10 public interface UserMapper {11 12 public User gYeMian(User u);13 14 public int sYeMian(User u);15 16 } service
package com.demo.service.impl;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import com.demo.domain.User;import com.demo.mapper.UserMapper;import com.demo.service.UserService;@Service(value = "userService")public class UserServiceImpl implements UserService{ @Autowired private UserMapper mapper; @Override public User gYeMian(User u) { User user = mapper.gYeMian(u); return user; } @Override public int sYeMian(User u) { int i = mapper.sYeMian(u); return i; }} controller
1 package com.demo.controller; 2 3 import javax.servlet.http.HttpServletRequest; 4 5 import org.springframework.beans.factory.annotation.Autowired; 6 import org.springframework.stereotype.Controller; 7 import org.springframework.web.bind.annotation.RequestMapping; 8 import org.springframework.web.bind.annotation.ResponseBody; 9 10 import com.demo.domain.User;11 import com.demo.service.UserService;12 13 @Controller14 @RequestMapping(value = "/uc")15 public class UserController {16 17 @Autowired18 private UserService userService;19 20 @ResponseBody21 @RequestMapping("/stemp.htm")22 private String sYeMian(String muBan, HttpServletRequest request){23 24 User u = new User();25 u.setMuBan(muBan);26 System.out.println("muBan=" + muBan);27 int i = userService.sYeMian(u);28 29 if (i>0){30 return "存储成功";31 }32 return "存储失败";33 }34 35 } 后来在网上看到网友说要用@Mapper注解，这才把问题解决了 至于具体原因，楼主还需要好好看看文档再来解释。
解决方案一：
mapper(Dao层)
1 package com.demo.mapper; 2 3 import org.apache.ibatis.annotations.Mapper; 4 5 import com.demo.domain.User; 6 7 @Mapper 8 public interface UserMapper { 9 10 public User gYeMian(User u);11 12 public int sYeMian(User u);13 14 } 解决方案二：
Application(启动类)
1 package com.demo; 2 3 import org.mybatis.spring.annotation.MapperScan; 4 import org.springframework.boot.SpringApplication; 5 import org.springframework.boot.autoconfigure.SpringBootApplication; 6 7 @SpringBootApplication 8 @MapperScan(value = "com.demo.mapper") 9 public class App 10 {11 public static void main(String[] args) throws Exception {12 SpringApplication.run(App.class, args);13 }14 } 原因：在mybatis-spring-boot-autoconfigure的jar包中有一个类 MybatisAutoConfiguration，在这个类中的registerBeanDefinitions方法告诉了我们
1 @Override 2 public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { 3 4 logger.debug("Searching for mappers annotated with @Mapper"); 5 6 ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry); 7 8 try { 9 if (this.resourceLoader != null) {10 scanner.setResourceLoader(this.resourceLoader);11 }12 13 List packages = AutoConfigurationPackages.get(this.beanFactory);14 if (logger.isDebugEnabled()) {15 for (String pkg : packages) {16 logger.debug("Using auto-configuration base package '{}'", pkg);17 }18 }19 20 scanner.setAnnotationClass(Mapper.class);21 scanner.registerFilters();22 scanner.doScan(StringUtils.toStringArray(packages));23 } catch (IllegalStateException ex) {24 logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex);25 }26 }