<!--spring-jdbc的依赖-->

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-jdbc</artifactId>

        </dependency>

        <!--mysql驱动-->

        <dependency>

            <groupId>mysql</groupId>

            <artifactId>mysql-connector-java</artifactId>

        </dependency>

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

spring.datasource.url=jdbc:mysql://localhost:3306/my_db?serverTimezone=GMT

spring.datasource.username=chy

spring.datasource.password=abcd

@Repository

public class UserDao implements UserDao{

    private JdbcTemplate jdbcTemplate;

    @Autowired

    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {

        this.jdbcTemplate = jdbcTemplate;

    }

    @Override

    public String queryUserById(Integer id){

        String sql = "select username from user_tb where id=?";

        String username = jdbcTemplate.queryForObject(sql, String.class, id);

        return username;

    }

}