SpringBoot中json转换的正确方式和位置
SpringBoot中json转换的正确方式和位置
提问于 2019-12-10 04:38:38
我正在做一个小的SpringBoot项目。将订单数据存储在postgres数据库中。我有一个API，它为我的前端返回json。我在问自己到底应该在哪个地方将我的数据转换为实际的json。我知道有几种方法可以做到这一点，但我想学习专业的方法。
假设订单包含id、date、customername、productid。在这个例子中，当我的前端被要求输入一个特定的名字时，我只需要order_date形式的date和product_id形式的productid。
可能的方式：
1)在我的CrudRepository中使用原生postgres查询：
@Query(value="SELECT json_build_object('order_date', o.date, 'product_id', productid)
from order where name=:name", nativeQuery = true)
List<Object> getOrderByName(@Param("name") String name);然后只需在控制器方法中调用此存储库方法。考虑到性能，转换成json可能是最快的方式。我现在面临的最大缺点是，你不能对crudrepository方法的返回值进行任何计算，因为它是一个特殊的postgres对象。例如，在测试中模拟这一点似乎很复杂。
2)选择crudrepository中的整个对象，然后在控制器中创建json：
Order findByName(String name);在控制器中，假设我的方法有一个返回类型ResponseEntity>，我将创建一个HashMap并返回它。
Order order = orderRepository.findByName("John Doe");
HashMap<String, String> jsonResult = new HashMap<>();
jsonResult.put("order_date", order.getName());
jsonResult.put("product_id", order.getProductId());
return jsonResult;这样做的好处是，我可以对从数据库中获得的order对象进行计算。我不必使用丑陋的sql查询，并且可以利用我的ORM系统的优点。最大的缺点是，我总是必须在每个控制器方法的末尾创建这个自定义的json，这感觉是错误的。
3)使用JPA投影。我没有尝试过，但我读到过(https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#projections)
做这个相当标准的动作的专业方法是什么？在更大的企业应用程序中是如何实现的？大型企业应用程序是否使用jpa crudrepository或如何在java中与数据库进行交互？
回答 2
Stack Overflow用户
回答已采纳
发布于 2019-12-10 23:21:37
假设您有一个“标准”项目结构:控制器、服务、存储库和域模型-为简洁起见，省略了import。
控制器
@Controller
@RequestMapping("/entities")
public final class TheController {
private static final Logger log = LoggerFactory.getLogger(TheController.class);
private final TheService service;
public TheController(final TheService service) {
this.service = service;
}
@GetMapping(produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Collection<JpaEntity>> getAll(final HttpServletRequest request) {
log.info("{} {}", request.getMethod(), request.getRequestURI());
return ResponseEntity.ok(service.searchAll());
}
@GetMapping(path = "{entity-id}", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> getById(final @PathVariable("entity-id") String id, final HttpServletRequest request) {
log.info("{} {}", request.getMethod(), request.getRequestURI());
final Optional<JpaEntity> result = service.searchById(UUID.fromString(id));
if (result.isPresent()) {
return ResponseEntity.ok(result.get());
}
return ResponseEntity.notFound().build();
}
@PostMapping(consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> post(@RequestBody @Valid final JpaEntity body, final HttpServletRequest request) {
log.info("{} {}", request.getMethod(), request.getRequestURI());
final URI uri = URI.create(String.format("%s/%s", request.getRequestURI(), service.save(body).getId())).normalize();
return ResponseEntity.created(uri).build();
}
}服务
@Service
@Transactional
public class TheService {
private static final Logger log = LoggerFactory.getLogger(TheService.class);
private TheRepository repository;
public TheService(final TheRepository repository) {
this.repository = repository;
}
@Transactional(readOnly = true)
public Collection<JpaEntity> searchAll() {
log.info("Retrieving all records...");
return repository.findAll();
}
@Transactional(readOnly = true)
public Optional<JpaEntity> searchById(final UUID id) {
log.info("Retrieving record with ID [{}]", id);
return repository.findById(id);
}
public JpaEntity save(final JpaEntity entity) {
log.info("Persisting record [{}]", entity);
return repository.save(entity);
}
}存储库
public interface TheRepository extends JpaRepository<JpaEntity, UUID> { }域模型
@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
abstract class AbstractPersistable<T> implements Serializable {
private static final long serialVersionUID = -537959523291969928L;
@Id
@JsonProperty("_id")
@GeneratedValue(generator = "uuid2")
@GenericGenerator(name = "uuid2", strategy = "uuid2")
@Column(name = "id", nullable = false, updatable = false, unique = true)
private T id;
@CreatedDate
@Column(name = "created_on", nullable = false, updatable = false)
private Instant createdOn;
@CreatedBy
@Column(name = "created_by", nullable = false)
private String createdBy;
@LastModifiedDate
@Column(name = "modified_on", nullable = false)
private Instant modifiedOn;
@LastModifiedBy
@Column(name = "modified_by", nullable = false)
private String modifiedBy;
@Version
@JsonProperty("_version")
private Integer version;
AbstractPersistable() { } // No-args constructor required by JPA spec
public T getId() { return id; }
public Instant getCreatedOn() { return createdOn; }
public String getCreatedBy() { return createdBy; }
public Instant getModifiedOn() { return modifiedOn; }
public String getModifiedBy() { return modifiedBy; }
public Integer getVersion() { return version; }
@Override
public String toString() {
return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE)
.append("id", id)
.append("createdOn", createdOn)
.append("createdBy", createdBy)
.append("modifiedOn", modifiedOn)
.append("modifiedBy", modifiedBy)
.append("version", version)
.toString();
}
}@Entity
@Immutable
@Table(name = "tb_name")
public final class JpaEntity extends AbstractPersistable<UUID> {
private static final long serialVersionUID = -1352464759104643303L;
@Column(name = "column1", length = 128, nullable = false)
private String one;
@Column(name = "column2", length = 128, nullable = false)
private String two;
private JpaEntity() { } // No-args constructor required by JPA spec
public JpaEntity(final String one, final String two) {
this.one = one;
this.two = two;
}
public String getOne() { return one; }
public String getTwo() { return two; }
@Override
public int hashCode() {
return Objects.hash(one, two);
}
@Override
public boolean equals(final Object obj) {
if (this == obj) { return true; }
if (!(obj instanceof JpaEntity)) { return false; }
final JpaEntity entity = (JpaEntity) obj;
return Objects.equals(one, entity.one) &&
Objects.equals(two, entity.two);
}
@Override
public String toString() {
return new ToStringBuilder(this, ToStringStyle.DEFAULT_STYLE)
.appendSuper(super.toString())
.append("one", one)
.append("two", two)
.toString();
}
}在向用户代理发送响应时，Spring Boot将为JpaEntity生成适当的JSON表示。
如果您希望控制哪些字段被序列化，则可以利用@JsonView注释在序列化/反序列化发生时包括/排除一组成员/字段，例如：
// CustomView.java
public interface CustomView { }
// JpaEntity.java
@JsonView(CustomView.class)
@Column(name = "column1", length = 128, nullable = false)
private String one;
// TheController.java
// When CustomView is used you are only going to get back what's annotated
// with CustomView in the given response type (JpaEntity on this case)
@JsonView(CustomView.class)
@GetMapping(path = "{entity-id}", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> getById(final @PathVariable("entity-id") String id, final HttpServletRequest request) {
log.info("{} {}", request.getMethod(), request.getRequestURI());
final Optional<JpaEntity> result = service.searchById(UUID.fromString(id));
if (result.isPresent()) {
return ResponseEntity.ok(result.get());
}
return ResponseEntity.notFound().build();
}或者，您可以使用另一种返回类型，例如：JpaEntityResponse。
public final class JpaEntityResponse {
private String one;
private String three;
private String andFour;
private JpaEntityResponse() { } // No-args constructor required by JPA spec
public JpaEntityResponse(final String one, final String two, final String andFour) {
this.one = one;
this.three = three;
this.andFour = andFour;
}
// ...getters
}然后，在“服务”类中的某个地方，假设您正在处理两个不同的域模型，并希望将一些字段聚合到JpaEntityResponse中，那么您只需要从中挑选感兴趣的成员/字段，构建JpaEntityResponse并返回它(同时还需要修改控制器的方法以返回此类型)。
Stack Overflow用户
发布于 2019-12-10 05:57:10
您首先需要一个可以映射到您的表的实体，以及该实体的crud/JPA存储库。您可以查询存储库(在控制器中)，并控制API要发回的字段(映射到表的列)。
下面是一个示例(您需要包含spring web依赖项才能启用自动Jackson配置)。在@JsonIgnore注释中，忽略JSON响应字段。但它将在java对象中可用。
@Entity
public class Order {
@Column(name = "product_id")
protected Long productId;
@Column(name = "order_date")
protected Date orderDate;
@JsonIgnore
@Column(name = "order_number")
protected Date orderNumber;
//setters and getters
}
@Transactional
public interface OrderRepo extends JpaRepository<Order, Long>{
}
@Controller
public class OrderController
{
public OrderController(){}
@Autowired
OrderRepo orderRepo;
@GetMapping(/orders/{id})
public Order findOrder(@PathVariable("id")long id)
{
return orderRepo.findById(id);
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/59256232
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