项目的pom文件内容如下：

<?xml version="1.0" encoding="UTF-8"?>

  4.0.0

  com.bes
  spring-colud
  1.0.0-SNAPSHOT
  
    user-service
  
  pom

  
    org.springframework.boot
    spring-boot-starter-parent
    2.0.4.RELEASE
  

  
    UTF-8
    UTF-8
    1.8
    Finchley.SR1
    2.0.3
    5.1.32
    1.2.5
  

  
    
      
      
        org.springframework.cloud
        spring-cloud-dependencies
        ${spring-cloud.version}
      

      
      
        tk.mybatis
        mapper-spring-boot-starter
        ${mapper.starter.version}
      

      
      
        com.github.pagehelper
        pagehelper-spring-boot-starter
        ${pageHelper.starter.version}
      

      
      
        mysql
        mysql-connector-java
        ${mysql.version}
      
    
  

  
    
      org.projectlombok
      lombok
      1.18.4
    
  

  
    
      
        org.springframework.boot
        spring-boot-maven-plugin
      
    
  

我的application.yml配置为：

server:
port: 8081
spring:
datasource:
url: jdbc:mysql://localhost:3306/springboot
username: root
password: root
mybatis:
type-aliases-package: com.bes.user.domain

UserDao为

package com.bes.user.dao;

import com.bes.user.domain.User;
import org.springframework.stereotype.Repository;
import tk.mybatis.mapper.common.Mapper;

public interface UserDao extends Mapper {
}

UserService为：

package com.bes.user.service;

import com.bes.user.dao.UserDao;
import com.bes.user.domain.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
@Transactional
public class UserService {
  @Autowired
  UserDao userDao;

  public User findById(Integer id) {
    User user = userDao.selectByPrimaryKey(id);
    return user;
  }
}

UserController为：

package com.bes.user.web;

import com.bes.user.domain.User;
import com.bes.user.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/user")
public class UserController {
  @Autowired
  UserService userService;

  @GetMapping("{id}")
  public User findById(@PathVariable("id")Integer id) {
    User user = userService.findById(id);
    return user;
  }
}

UserApplication为：

package com.bes;

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

@SpringBootApplication
@MapperScan("com.bes.user.dao")
public class UserApplication {
  public static void main(String[] args) {
    SpringApplication.run(UserApplication.class, args);
  }
}

上述代码是填坑之后的，而错误的原因也非常奇葩在UserService中自动注入UserDao时提示我没有UserDao这个bean.

于是我就在UserDao上加了一个@Repository注解，如下图：

而后UserService不在报错了，运行UserApplication项目正常起来了。

但是通过浏览器访问时却一片空白。

这时在回到IDEA查看下方日志多了两行东西。1111是我调试时让它打印的无关东西。

这个奇怪的错误搞了我几个小时。最后发现不因给在UserDao上加@Reposity注解。UserService中注入Use人Dao报错时应如下处理：

1、鼠标点击报错的UserService中报错的UserDao

2、ALT+ENTER

3、选择第一个选项

4、在选择disable开头的选项