springboot项目如何实现从MySQL数据库中查询数据

1. 配置pom.xml文件，添加MySQL驱动依赖

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

2. 配置application.properties文件，指定MySQL数据库连接信息

spring.datasource.url=jdbc:mysql://localhost:3306/testdb
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

3. 创建数据实体类，使用JPA注解定义表名、字段名等信息

@Entity
@Table(name = "user")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "age")
    private Integer age;

    // 省略getters和setters方法
}

4. 创建数据访问层接口，继承JpaRepository，使用JPA内置方法实现数据访问

public interface UserRepository extends JpaRepository<User, Long> {

    List<User> findByName(String name);

    List<User> findByAgeGreaterThan(Integer age);
}

5. 在业务层中调用数据访问层接口方法，获取数据

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public List<User> findByName(String name) {
        return userRepository.findByName(name);
    }

    public List<User> findByAgeGreaterThan(Integer age) {
        return userRepository.findByAgeGreaterThan(age);
    }
}