springboot + mybatis 的项目，实现简单的CRUD

以前都是用Springboot+jdbcTemplate实现CRUD

但是趋势是用mybatis，今天稍微修改，创建springboot + mybatis 的项目，实现简单的CRUD

上图是项目的目录结构，创建一个user实体，包含id，姓名，手机，密码，flag等信息，然后对用户进行增删查改。

drop table if exists user;

CREATE TABLE `user` (
  id tinyint(4) NOT NULL AUTO_INCREMENT,
  name varchar(200) NOT NULL,
  age int(11) NOT NULL,、
  phone varchar(20) NOT NULL,
  password varchar(20) NOT NULL,
  flag int(4),
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

用Intellij IDEA进行开发，创建一个新的springboot项目，选中SQL中的mybaits，生成之后默认带有DemoApplication主函数启动类，最后启动的时候要在主函数上添加mapper扫描@MapperScan("com.example.demo.mapper") //扫描全部mapper

其他的代码依次如下： User

public class User implements Serializable {
	private Long id;
	private String name;
	private int age;
	private String phone;
	private String password;
	private boolean flag;

    省略了getter and setter
}

userService

package com.example.demo.service;

import com.example.demo.pojo.User;

import java.util.List;

public interface userService {

	List<User> findAll();

	List<User> selectAll();

	List<User> selectById(int id);

	int create(User user);

	int updateUserById(User user);

	int deleteUserById(int id);
}

userServiceImp

package com.example.demo.serviceImp;

import com.example.demo.mapper.userMapper;
import com.example.demo.pojo.User;
import com.example.demo.service.userService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class userServiceImp implements userService {

	@Autowired
	private userMapper userMapper;

	public List<User> findAll() {
		System.err.println("查询所有用户接口");
		List<User> list = userMapper.findAll();
		return list;
		
	}

	@Override
	public List<User> selectAll() {
		List<User> list = userMapper.selectAll();
		return list;
	}

	@Override
	public List<User> selectById(int id) {
		List<User> list = userMapper.selectById(id);
		return list;
	}


	@Override
	public int create(User user) {
		int count = userMapper.create(user);
		return count;
	}

	@Override
	public int updateUserById(User user) {
		int count = userMapper.updateUserById(user);
		return count;
	}

	@Override
	public int deleteUserById(int id) {
		int count = userMapper.deleteUserById(id);
		return count;
	}

}

　　userMapper

package com.example.demo.mapper;

import com.example.demo.pojo.User;

import java.util.List;


public interface userMapper {

	List<User> findAll();

	List<User> selectAll();

	List<User> selectById(int id);

	int create(User user);

	int updateUserById(User user);

	int deleteUserById(int id);
}

userController

package com.example.demo.controller;

import com.example.demo.pojo.User;
import com.example.demo.serviceImp.userServiceImp;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.ModelAndView;

import java.util.List;

@Api(tags = {"demo接口"})
@Controller
@RequestMapping("user")
public class userController {

	@Autowired
	private userServiceImp userService;

    @ApiOperation(value = "显示全部用户的信息倒序")
    @RequestMapping("userLists")
	@ResponseBody
	public List<User> showUsers() {
		List<User> list = userService.findAll();
		return list;
	}

    @ApiOperation(value = "显示全部用户的信息")
	@RequestMapping("selectAll")
	@ResponseBody
	public List<User> selectAll() {
		List<User> list = userService.selectAll();
		return list;
	}

    @ApiOperation(value = "根据ID查询用户的信息")
	@RequestMapping("selectById")
	@ResponseBody
	public List<User> selectById(int id) {
		List<User> list = userService.selectById(300);
		return list;
	}

    @ApiOperation(value = "创建新用户信息")
	@PostMapping("create")
	@ResponseBody
	public String create(User user) {
		int count = userService.create(user);
		System.out.println(count);
		if (count>0)
		return ("成功添加"+count+"条记录");
		else
			return "添加用户失败";
	}

    @ApiOperation(value = "根据ID更新用户信息")
    @PostMapping("updateUserById")
    @ResponseBody
    public String updateUserById(User user) {
        int count = userService.updateUserById(user);
        System.out.println(count);
        if (count>0)
            return ("成功更新"+count+"条记录");
        else
            return "更新用户失败";
    }

    @ApiOperation(value = "根据ID删除用户信息")
    @PostMapping("deleteUserById")
    @ResponseBody
    public String deleteUserById(int id) {
        int count = userService.deleteUserById(id);
        System.out.println(count);
        if (count>0)
            return ("成功删除"+count+"条记录");
        else
            return "删除用户失败";
    }



}

　　userMapper.xml 映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.mapper.userMapper">

    <resultMap id="userResultMap" type="com.example.demo.pojo.User">
        <id column="id" property="id" jdbcType="BIGINT"/>
        <result column="name" property="name" jdbcType="VARCHAR"/>
        <result column="age" property="age" jdbcType="VARCHAR"/>
        <result column="phone" property="phone" jdbcType="VARCHAR"/>
        <result column="password" property="password" jdbcType="VARCHAR"/>
        <result column="flag" property="flag" jdbcType="BIGINT"/>
    </resultMap>
    
	
	<select id="findAll" resultMap="userResultMap">
     SELECT id,name,age,phone,password,flag FROM user order by id desc
	</select>

    <select id="selectById" parameterType ="int" resultMap="userResultMap">
        select * from user where id = #{id}
    </select>

    <select id="selectAll" resultMap="userResultMap">
        select * from user order by id desc
    </select>

    <insert id="create" parameterType="com.example.demo.pojo.User">
     insert into user(name,age,phone,password,flag)  values (#{name},#{age},#{phone},#{password},#{flag})
	</insert>

    <update  id="updateUserById" parameterType="com.example.demo.pojo.User">
        update user set name = #{name},age =#{age},phone =#{phone},password = #{password},flag = #{flag} where id = #{id}
    </update>

    <delete  id="deleteUserById" parameterType ="int">
        delete from user where id = #{id}
    </delete>
	

  
</mapper>

1. Mapper method 'com.example.demo.mapper.userMapper.create attempted to return null from a method with a primitive return type (int).] with root cause

是新增用户信息接口，发现用户信息已经成功插入数据库，但是页面提示

There was an unexpected error (type=Internal Server Error, status=500).

Mapper method 'com.example.demo.mapper.userMapper.create attempted to return null from a method with a primitive return type (int).