通过其 ID 序列化 JAXB 对象? [英] Serialize a JAXB object via its ID?
问题描述
在我的数据模型中,我有这样的效果:
In my data model, I have something to this effect:
@Entity
public class Target {
@Id
@GeneratedValue
private Long id;
/* ...etc... */
}
@Entity
public class Dependency {
@Id
@GeneratedValue
private Long id;
@ManyToOne(optional=false)
@Column(name="target_id")
private Target target;
/* ...etc... */
}
我已经很好地序列化了 Target
,但是我需要序列化 Dependency
.基本上,我需要的是这样的:
I'm already serializing Target
just fine, but I need to serialize Dependency
. Essentially, what I need is something like this:
<dependency>
<id>100</id>
<targetId>200</targetId>
</dependency>
有没有办法在不修改我的模型的情况下在 JAXB 注释中做到这一点?
Is there a way to do this in JAXB annotations without modifying my model?
推荐答案
对于这个用例,您可以使用 XmlAdapter
:
You could use an XmlAdapter
for this use case:
package forum7278406;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class TargetAdapter extends XmlAdapter<Long, Target> {
@Override
public Long marshal(Target target) throws Exception {
return target.getId();
}
@Override
public Target unmarshal(Long id) throws Exception {
Target target = new Target();
target.setId(id);
return target;
}
}
XmlAdapter
使用 @XmlJavaTypeAdapter
注释注册在 Dependency
类上:
The XmlAdapter
is registered on the Dependency
class using the @XmlJavaTypeAdapter
annotation:
package forum7278406;
import javax.persistence.*;
import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
@Entity
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Dependency {
@Id
@GeneratedValue
private Long id;
@ManyToOne(optional=false)
@Column(name="target_id")
@XmlJavaTypeAdapter(TargetAdapter.class)
private Target target;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Target getTarget() {
return target;
}
public void setTarget(Target target) {
this.target = target;
}
}
走得更远
我们可以使用 EntityManager
从数据库中查询相应的实例,而不是仅仅创建 Target
的新实例.我们的 XmlAdapter
将更改为如下所示:
Instead of just creating a new instance of Target
we could use an EntityManager
to query the corresponding instance from the database. Our XmlAdapter
would be changed to look something like:
package forum7278406;
import javax.persistence.EntityManager;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class TargetAdapter extends XmlAdapter<Long, Target> {
EntityManager entityManager;
public TargetAdapter() {
}
public TargetAdapter(EntityManager entityManager) {
this.entityManager = entityManager;
}
@Override
public Long marshal(Target target) throws Exception {
return target.getId();
}
@Override
public Target unmarshal(Long id) throws Exception {
Target target = null;
if(null != entityManager) {
target = entityManager.find(Target.class, id);
}
if(null == target) {
target = new Target();
target.setId(id);
}
return target;
}
}
现在要在我们的 XmlAdapter
上设置 EntityManager
的实例,我们可以执行以下操作:
Now to set the instance of EntityManager
on our XmlAdapter
, we can do the following:
Unmarshaller umarshaller = jaxbContext.createUnmarshaller();
TargetAdapter targetAdatper = new TargetAdapter(entityManager);
unmarshaller.setAdapter(targetAdapter);
这篇关于通过其 ID 序列化 JAXB 对象?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!