详解SpringBoot实现JPA的save方法不更新null属性

public class SimpleJpaRepositoryImpl<T, ID> extends SimpleJpaRepository<T, ID> {

  private final JpaEntityInformation<T, ?> entityInformation;
  private final EntityManager em;

  @Autowired
  public SimpleJpaRepositoryImpl(JpaEntityInformation<T, ?> entityInformation, EntityManager entityManager) {
    super(entityInformation, entityManager);
    this.entityInformation = entityInformation;
    this.em = entityManager;
  }

  /**
   * 通用save方法 ：新增/选择性更新
   */
  @Override
  @Transactional
  public <S extends T> S save(S entity) {
    //获取ID
    ID entityId = (ID) entityInformation.getId(entity);
    Optional<T> optionalT;
    if (StringUtils.isEmpty(entityId)) {
      String uuid = UUID.randomUUID().toString();
      //防止UUID重复
      if (findById((ID) uuid).isPresent()) {
        uuid = UUID.randomUUID().toString();
      }
      //若ID为空 则设置为UUID
      new BeanWrapperImpl(entity).setPropertyValue(entityInformation.getIdAttribute().getName(), uuid);
      //标记为新增数据
      optionalT = Optional.empty();
    } else {
      //若ID非空 则查询最新数据
      optionalT = findById(entityId);
    }
    //获取空属性并处理成null
    String[] nullProperties = getNullProperties(entity);
    //若根据ID查询结果为空
    if (!optionalT.isPresent()) {
      em.persist(entity);//新增
      return entity;
    } else {
      //1.获取最新对象
      T target = optionalT.get();
      //2.将非空属性覆盖到最新对象
      BeanUtils.copyProperties(entity, target, nullProperties);
      //3.更新非空属性
      em.merge(target);
      return entity;
    }
  }

  /**
   * 获取对象的空属性
   */
  private static String[] getNullProperties(Object src) {
    //1.获取Bean
    BeanWrapper srcBean = new BeanWrapperImpl(src);
    //2.获取Bean的属性描述
    PropertyDescriptor[] pds = srcBean.getPropertyDescriptors();
    //3.获取Bean的空属性
    Set<String> properties = new HashSet<>();
    for (PropertyDescriptor propertyDescriptor : pds) {
      String propertyName = propertyDescriptor.getName();
      Object propertyValue = srcBean.getPropertyValue(propertyName);
      if (StringUtils.isEmpty(propertyValue)) {
        srcBean.setPropertyValue(propertyName, null);
        properties.add(propertyName);
      }
    }
    return properties.toArray(new String[0]);
  }
}

@EnableJpaRepositories(value = "com.hehe.repository", repositoryBaseClass = SimpleJpaRepositoryImpl.class)
@SpringBootApplication
public class JpaApplication {

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

@Entity
@Table(name = "T_USER")
@JsonIgnoreProperties({"handler","hibernateLazyInitializer"})
public class User {
  @Id
  private String userId;
  private String username;
  private String password;
  //省略GET/SET
}
public interface UserRepository extends JpaRepository<User, String> {
}

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

drop table if exists t_user;
create table t_user (
 user_id varchar(50),
 username varchar(50),
 password varchar(50)
);

insert into t_user values ('1', 'admin', 'admin');
insert into t_user values ('2', 'yizhiwazi', '123456');

@RestController
public class UserController {

  @Autowired
  private UserRepository userRepository;

  @RequestMapping("/")
  public User get() {

    userRepository.save(new User("1", "", null));

    return userRepository.findById("1").get();
  }
}