springboot 使用 MyBatis 连接 mysql 数据库(2021.01.25)

本文依照 (https://blog.csdn.net/dkbnull/article/details/87278817 Spring Boot整合MyBatis连接数据库) 的实践记录,主要实践MyBatis映射文件实现数据库的连接.

备注:

1. MyBatis查询数据库的方式有三种,xml文件查询复杂语句更好一些. https://www.cnblogs.com/thisiswhy/p/12909994.html
2. 因为存在文件引用的原因,建议按照教程走完之后运行,中间可能存在引用文件还没有创建导致报错
3. 如果连接数据库失败,请检查账号密码以及url前面的//斜杠数量是否正确,以及表名是否正确
4. vscode搜索相关教程也可以实现运行springboot,自动导入包、自动生成get set等

开发环境:

• IDE：eclipse
• jdk：15.0.1
• Spring Boot：2.3.7.RELEASE
• Maven：3.6.3
• MySQL：8.0.18

创建数据库:

　　1.创建 spring_boot_blog 库

　　2.创建表 admin 并写入一条数据

CREATE TABLE `admin` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(50) NOT NULL,
 PRIMARY KEY (`id`),
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

引入依赖:

<dependencies>
    //pom.xml追加
    <dependencies>
    <dependency>
        <groupId>org.mybatis.spring.boot</groupId>
        <artifactId>mybatis-spring-boot-starter</artifactId>
        <version>2.1.4</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        // mysql 8.+版本需要指定版本号
        <version>8.0.18</version>
    </dependency> 
</dependencies>        

MyBatis配置:

　　1.在resources文件夹下新建mapper文件夹，用于存放MyBatis映射文件

　　

　　2.application.properties 增加MyBatis配置信息 (参考文章内是application.yml 增加MyBatis配置信息 )

#https://blog.csdn.net/fu18838928050/article/details/105057704

#mysql配置
spring.datasource.url=jdbc:mysql://localhost:3306/spring_boot_blog?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone = GMT
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
server.tomcat.uri-encoding=UTF-8

#MyBatis配置
mybatis.mapper-locations=classpath:mapper/*.xml
#这个地方写你model存放所在的包路径
mybatis.type-aliases-package=com.example.demo.model

　　2.在启动文件内增加注解@MapperScan("com.example.demo.dao")，括号内对应DAO层的包名

package com.example.demo;

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

@SpringBootApplication
@MapperScan("com.example.demo.dao")
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

编写业务逻辑代码:

　　1.在 com.example.demo 下创建 com.example.demo.mode 包并创建 TestModel 类

package com.example.demo.model;

public class TestModel {

    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

　　2.在 com.example.demo 下创建 com.example.demo.dao包并创建 TestMapperV2 类

package com.example.demo.dao;

import java.util.List;

import com.example.demo.model.TestModel;
import com.example.demo.model.*;
public interface TestMapperV2 {
     List<TestModel> select();
     
     int insert(TestModel testModel);
}

　　3.在 com.example.demo 下创建 com.example.demo.service 包并创建 MySQLTestServiceV2 类

package com.example.demo.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.example.demo.dao.TestMapperV2;
import com.example.demo.model.TestModel;

@Service
public class MySQLTestServiceV2 {
    @Autowired
    private TestMapperV2 testMapperV2;  //这里会有报错，不用管

    public List<TestModel> select() {
        return testMapperV2.select();
    }

    public int insert(int id, String name) {
        TestModel testModel = new TestModel();
        testModel.setId(id);
        testModel.setName(name);

        return testMapperV2.insert(testModel);
    }
}

　　4.在 com.example.demo 下创建 com.example.demo.controller包并创建 MySQLTestControllerV2 类

package com.example.demo.controller;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Scope;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import com.example.demo.model.TestModel;
import com.example.demo.service.MySQLTestServiceV2;

@RestController
@Scope("prototype")
@RequestMapping("/mysql/test")
public class MySQLTestControllerV2 {
    @Autowired
    private MySQLTestServiceV2 mySQLTestServiceV2;

    @PostMapping(value = "/selectV2")
    public List<TestModel> select() throws Exception {
        return mySQLTestServiceV2.select();
    }

    @PostMapping(value = "/insertV2")
    public int insert(@RequestParam(value = "id") int id,
                      @RequestParam(value = "name") String name) throws Exception {
        return mySQLTestServiceV2.insert(id, name);
    }
}

　　5.创建MyBatis映射文件,在 resources/mapper 下新建映射文件 TestMapper.xml,关于xml详细配置请看官方文档 https://mybatis.org/mybatis-3/zh/index.html

<?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.dao.TestMapperV2">
    <resultMap id="BaseResultMap" type="com.example.demo.model.TestModel">
        <id column="id" property="id" jdbcType="INTEGER"/>
        <result column="name" property="name" jdbcType="VARCHAR"/>
    </resultMap>
    <sql id="Base_Column_List">
        id, name
    </sql>
    <select id="select" resultMap="BaseResultMap">
        select
        <include refid="Base_Column_List"/>
        from admin
    </select>
    <insert id="insert" parameterType="com.example.demo.model.TestModel">
        insert into admin (id, name
        )
        values (#{id,jdbcType=INTEGER}, #{name,jdbcType=VARCHAR}
        )
    </insert>
</mapper>

测试运行:

　　Post 请求 localhost:8080/mysql/test/selectV2