java - 在spring boot中将Entity映射到DTO时的循环依赖
问题描述
我有两个实体类:
@Data
@Entity
@Table(name="Foo", schema="REF_DATA")
public class Foo {
private Long fooId;
private String fooName;
@OneToMany(mappedBy="foo")
@ToString.Exclude
private List<Bar> bars;
}
@Data
@Entity
@Table(name="Bar", schema="REF_DATA")
public class Bar {
private Long barId;
private String barName;
@ManyToOne
@JoinColumn(name="fooId")
private Foo foo;
}
他们各自的 DTO 看起来像:
public class FooDto {
private Long fooId;
private String fooName;
@JsonIgnoreProperties("foo")
private List<BarDto> bars;
}
public class BarDto {
private Long barId;
private String barName;
@JsonIgnoreProperties("bars") //added to avoid the cyclic dependency
private FooDto foo;
}
当用户调用时/getAllData
,我们将返回以下 DTO:
public class FooBar {
List<FooDto> foo;
List<BarDto> bars;
}
我们能够使用 JPA 从后端获取数据,但是在将实体映射到 Dto 时出错。映射器代码如下所示:
public interface DomainToDtoMapper<E extends BaseEntity, D extends BaseDto> {
D mapDomainToDto(E domain);
}
public class FooDomainToDtoMapper implements DomainToDtoMapper<Foo, FooDto> {
@Override
public FooDto mapDomainToDto(Foo domain) {
FooDto fooDto = new FooDto();
FooDto.setfooId(domain.getfooId());
FooDto.setfooName(domain.getfooName());
if (domain.getBars() != null) {
BarDomainToDtoMapper barDomainToDtoMapper= new BarDomainToDtoMapper();
fooDto.setBars(domain.getBars().stream()
.map(barDomainToDtoMapper::mapDomainToDto)
.collect(Collectors.toList()));
}
return fooDto;
}
}
public class BarDomainToDtoMapper implements DomainToDtoMapper<Bar, BarDto> {
@Override
public BarDto mapDomainToDto(Bar domain) {
BarDto barDto = new BarDto();
barDto.setBarId(domain.getBarId());
barDto.setBarName(domain.getBarName());
//works fine if we remove this If condition but Bar won't have Foo in final output
if (domain.getFoo() != null) {
FooDomainToDtoMapper fooDomainToDtoMapper= new FooDomainToDtoMapper();
barDto.setFoo(domain.getFoo());
}
return barDto ;
}
}
映射Bar
到时,BarDto
我们收到 StackOverflow 错误。
org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.StackOverflowError
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) [spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) [spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) [tomcat-embed-core-9.0.37.jar:4.0.FR]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) [spring-webmvc-5.2.8.RELEASE.jar:5.2.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) [tomcat-embed-core-9.0.37.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-9.0.37.jar:9.0.37]
Caused by: java.lang.StackOverflowError: null
at com.jpmorgan.markets.dto.mapper.FooDomainToDtoMapper .mapDomainToDto(FooDomainToDtoMapper .java:17) ~[classes/:na]
at com.jpmorgan.markets.dto.mapper.BarDomainToDtoMapper .mapDomainToDto(BarDomainToDtoMapper .java:23) ~[classes/:na]
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[na:1.8.0_231]
at java.util.Iterator.forEachRemaining(Iterator.java:116) ~[na:1.8.0_231]
at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801) ~[na:1.8.0_231]
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482) ~[na:1.8.0_231]
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472) ~[na:1.8.0_231]
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[na:1.8.0_231]
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_231]
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[na:1.8.0_231]
BarDto
同样,FooDto
如果用户通过 Id 请求它们,我们希望返回个人。但问题是,在最终输出中,一个必须包含另一个对象。我尝试在实体中添加@JsonBackReference
和@JsonManagedReference
,仍然得到相同的错误。是因为我们将实体显式映射到 DTO 而不是直接返回实体吗?有没有更好的方法来做到这一点而不使用类似的东西Mapstruct
?
解决方案
You need to use @JsonBackReference
and @JsonManagedReference
as used in the below in below code.
Foo Entity
@Data
@Entity
@Table(name="Foo", schema="REF_DATA")
public class Foo {
private Long fooId;
private String fooName;
@OneToMany(mappedBy="foo")
@ToString.Exclude
@JsonManagedReference
private List<Bar> bars;
}
Bar Entity
@Data
@Entity
@Table(name="Bar", schema="REF_DATA")
public class Bar {
private Long barId;
private String barName;
@ManyToOne
@JoinColumn(name="fooId")
@JsonBackReference
private Foo foo;
}
*Note: If still faced any problem then try removing @JsonManagedReference
from Foo
entity.
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