springboot + mybatis 的專案，實現簡單的CRUD

摘要： 以前都是用Springboot+jdbcTemplate實現CRUD 但是趨勢是用mybatis，今天稍微修改，建立springboot + mybatis 的專案，實現簡單的CRUD  上圖是專案的目錄結構，建立一個user實體，包含id，姓名，手機，密碼，flag...

以前都是用Springboot+jdbcTemplate實現CRUD

但是趨勢是用mybatis，今天稍微修改，建立springboot + mybatis 的專案，實現簡單的CRUD 

上圖是專案的目錄結構，建立一個user實體，包含id，姓名，手機，密碼，flag等資訊，然後對使用者進行增刪查改。

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進行開發，建立一個新的springboot專案，選中SQL中的mybaits，生成之後預設帶有DemoApplication主函式啟動類，最後啟動的時候要在主函式上新增mapper掃描@MapperScan("com.example.demo.mapper") //掃描全部mapper

其他的程式碼依次如下： 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("查詢所有使用者介面");
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介面"})
@Controller
@RequestMapping("user")
public class userController {

@Autowired
private userServiceImp userService;

@ApiOperation(value = "顯示全部使用者的資訊倒序")
@RequestMapping("userLists")
@ResponseBody
public List<User> showUsers() {
List<User> list = userService.findAll();
return list;
}

@ApiOperation(value = "顯示全部使用者的資訊")
@RequestMapping("selectAll")
@ResponseBody
public List<User> selectAll() {
List<User> list = userService.selectAll();
return list;
}

@ApiOperation(value = "根據ID查詢使用者的資訊")
@RequestMapping("selectById")
@ResponseBody
public List<User> selectById(int id) {
List<User> list = userService.selectById(300);
return list;
}

@ApiOperation(value = "建立新使用者資訊")
@PostMapping("create")
@ResponseBody
public String create(User user) {
int count = userService.create(user);
System.out.println(count);
if (count>0)
return ("成功新增"+count+"條記錄");
else
return "新增使用者失敗";
}

@ApiOperation(value = "根據ID更新使用者資訊")
@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+"條記錄");
else
return "更新使用者失敗";
}

@ApiOperation(value = "根據ID刪除使用者資訊")
@PostMapping("deleteUserById")
@ResponseBody
public String deleteUserById(int id) {
int count = userService.deleteUserById(id);
System.out.println(count);
if (count>0)
return ("成功刪除"+count+"條記錄");
else
return "刪除使用者失敗";
}



}

userMapper.xml 對映檔案

<?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>

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

<deleteid="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

是新增使用者資訊介面，發現使用者資訊已經成功插入資料庫，但是頁面提示

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).