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);
      }
    }