如何解决春季启动时将实体映射到DTO时的循环依赖性
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;
}
它们各自的DTO如下:
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;
}
当用户致电/getAllData
时,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Entity映射到Dto时遇到错误。映射器代码如下:
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 ;
}
}
将Bar
映射到BarDto
时,我们遇到了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]
类似地,如果用户按ID要求返回个人BarDto
和FooDto
,我们希望返回它们。但问题是,在最终输出中,一个对象必须包含另一个对象。我尝试在实体中添加@JsonBackReference
和@JsonManagedReference
,但仍然遇到相同的错误。是否因为我们将实体显式映射到DTO而不是直接返回实体?不用使用Mapstruct
之类的方法,还有其他更好的方法吗?
解决方法
您需要使用下面的代码中的@JsonBackReference
和@JsonManagedReference
。
Foo实体
@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;
}
酒吧实体
@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;
}
*注意:如果仍然遇到任何问题,请尝试从@JsonManagedReference
实体中删除Foo
。
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