Springboot怎么实现注册功能并且把注册信息添加到数据库，数据库使用mysql，请给我一个完整代码

好的，下面是一个完整的 Spring Boot 注册功能的实现代码，使用 MySQL 数据库：

1. 创建 User 实体类

@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true)
    private String username;

    @Column(nullable = false)
    private String password;

    @Column(nullable = false, unique = true)
    private String email;

    // 省略 getter 和 setter 方法
}

2. 创建 UserRepository 接口

public interface UserRepository extends JpaRepository<User, Long> {
    User findByUsername(String username);
}

3. 创建 UserService 类

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public User register(User user) throws BusinessException {
        // 判断用户名是否已经存在
        if (userRepository.findByUsername(user.getUsername()) != null) {
            throw new BusinessException("用户名已存在");
        }

        // 对密码进行加密
        user.setPassword(DigestUtils.md5DigestAsHex(user.getPassword().getBytes()));

        // 保存用户信息到数据库
        return userRepository.save(user);
    }
}

4. 创建 UserController 类

@RestController
public class UserController {
    @Autowired
    private UserService userService;

    @PostMapping("/register")
    public ResponseEntity<?> register(@RequestBody User user) throws BusinessException {
        userService.register(user);

        return ResponseEntity.ok().build();
    }
}

5. 创建 application.properties 配置文件

在 src/main/resources 目录下创建 application.properties 文件，添加以下配置：

spring.datasource.url=jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
spring.datasource.username=root
spring.datasource.password=123456
spring.jpa.hibernate.ddl-auto=create

其中，spring.datasource.url 是数据库的连接地址，mydb 是数据库名，root 是数据库用户名，123456 是数据库密码。

6. 运行程序

启动程序，访问 http://localhost:8080/register，提交注册信息即可将用户信息保存到数据库。

完整代码见下面：

User.java

@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true)
    private String username;

    @Column(nullable = false)
    private String password;

    @Column(nullable = false, unique = true)
    private String email;

    public Long getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

UserRepository.java

public interface UserRepository extends JpaRepository<User, Long> {
    User findByUsername(String username);
}

UserService.java

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public User register(User user) throws BusinessException {
        // 判断用户名是否已经存在
        if (userRepository.findByUsername(user.getUsername()) != null) {
            throw new BusinessException("用户名已存在");
        }

        // 对密码进行加密
        user.setPassword(DigestUtils.md5DigestAsHex(user.getPassword().getBytes()));

        // 保存用户信息到数据库
        return userRepository.save(user);
    }
}

UserController.java

@RestController
public class UserController {
    @Autowired
    private UserService userService;

    @PostMapping("/register")
    public ResponseEntity<?> register(@RequestBody User user) throws BusinessException {
        userService.register(user);

        return ResponseEntity.ok().build();
    }
}

application.properties

spring.datasource.url=jdbc:mysql://localhost:3306/mydb?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai
spring.datasource.username=root
spring.datasource.password=123456
spring.jpa.hibernate.ddl-auto=create

注意：以上代码仅供参考，具体实现方式可以根据实际需求进行调整。