Spring Boot：Consider defining a bean of type '*.*.*' in your configuration解决方案

　　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
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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)

 package com.demo.mapper;

 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.stereotype.Repository;

 import com.demo.domain.User;

 //@Component
 @Repository
 public interface UserMapper {

     public User gYeMian(User u);

     public int sYeMian(User u);

 }

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

 package com.demo.controller;

 import javax.servlet.http.HttpServletRequest;

 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.ResponseBody;

 import com.demo.domain.User;
 import com.demo.service.UserService;

 @Controller
 @RequestMapping(value = "/uc")
 public class UserController {

     @Autowired
     private UserService userService;

     @ResponseBody
     @RequestMapping("/stemp.htm")
     private String sYeMian(String muBan, HttpServletRequest request){

         User u = new User();
         u.setMuBan(muBan);
         System.out.println("muBan=" + muBan);
         int i = userService.sYeMian(u);

         if (i>0){
             return "存储成功";
         }
             return "存储失败";
     }

 }

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)

 package com.demo.mapper;

 import org.apache.ibatis.annotations.Mapper;

 import com.demo.domain.User;

 @Mapper
 public interface UserMapper {

     public User gYeMian(User u);

     public int sYeMian(User u);

 }

解决方案二：

Application(启动类)

 package com.demo;

 import org.mybatis.spring.annotation.MapperScan;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;

 @SpringBootApplication
 @MapperScan(value = "com.demo.mapper")
 public class App
 {
     public static void main(String[] args) throws Exception {
         SpringApplication.run(App.class, args);
     }
 }

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

 @Override
     public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

       logger.debug("Searching for mappers annotated with @Mapper");

       ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);

       try {
         if (this.resourceLoader != null) {
           scanner.setResourceLoader(this.resourceLoader);
         }

         List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
         if (logger.isDebugEnabled()) {
           for (String pkg : packages) {
             logger.debug("Using auto-configuration base package '{}'", pkg);
           }
         }

         scanner.setAnnotationClass(Mapper.class);
         scanner.registerFilters();
         scanner.doScan(StringUtils.toStringArray(packages));
       } catch (IllegalStateException ex) {
         logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex);
       }
     }