1、这里只是单纯的演示比较原始的数据库连接，暂时我们先不看如何加入mybatis和其它配置。
首先pom.xml引入依赖：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.0</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.wlm</groupId>
    <artifactId>springboot-04-data</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot-04-data</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2、在配置文件中，引入数据库配置
application.yml

spring:
  datasource:
    username: root
    password: admin
    #?serverTimezone=UTC解决时区的报错
    url: jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8
    driver-class-name: com.mysql.cj.jdbc.Driver

3、最后做一个controller层
JDBCController.java

package com.wlm.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;
import java.util.Map;

@RestController
public class JDBCController {
    @Autowired
    JdbcTemplate jdbcTemplate;
    //查询数据库的所有信息
    //如果没有实体类，我们直接用map获取数据库中的东西
    @GetMapping("/userList")
    public List<Map<String,Object>> userList(){
        String sql = "select * from user";
        List<Map<String, Object>> list_maps = jdbcTemplate.queryForList(sql);
        return  list_maps;
    }
    @GetMapping("/addUser")
    public String addUser(){
        String sql = "insert into mybatis.user(id,name,pwd) values (1,'小马','88378')";
        jdbcTemplate.update(sql);
        return "addUser-ok";
    }
    @GetMapping("/updateUser/{id}")
    public String updateUser(@PathVariable("id") int id){
        String sql = "update mybatis.user set name=?,pwd=? where id="+id;
        //封装
        Object[] objects = new Object[2];
        objects[0] = "小彭";
        objects[1] = "456789";
        jdbcTemplate.update(sql,objects);
        return "updateUser-ok";
    }
    @GetMapping("/deleteUser/{id}")
    public String deleteUser(@PathVariable("id") int id){
        String sql = "delete from mybatis.user where id = ?";
        jdbcTemplate.update(sql,id);
        return "deleteUser-ok";
    }
}

4、当然我们也可以在测试中查看数据源的信息：
SpringbootDataApplicationTests.java

package com.wlm;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

@SpringBootTest
class Springboot04DataApplicationTests {
    @Autowired
    DataSource dataSource;
    @Test
    void contextLoads() throws SQLException {
        //查看默认的数据源: com.zaxxer.hikari.HikariDataSource
        System.out.println(dataSource.getClass());
        //获得数据库连接
        Connection connection = dataSource.getConnection();
        System.out.println(connection);
        //我们以后会经常看见xxxxTemplate，这个是spring boot已经配置好的模板@bean，拿来即用
        //关闭
        connection.close();
    }

}