通过它的ID序列化一个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：

  @Entity 
 public class Target { b 
 $ b @Id 
 @GeneratedValue 
私人长ID; 
 
 / * ... etc ... * / 
} 
 
 @实体
公共类别依赖关系{
 
 @Id 
 @GeneratedValue 
私人长ID; 
 
 @ManyToOne（可选= false）
 @Column（name =target_id）
私人目标目标; 
 
 / * ... etc ... * / 
} 
  

我已经序列化 Target 就好了，但我需要序列化 Dependency 。基本上，我需要的是这样的：

 <依赖关系> 
< id> 100< / id> 
< targetId> 200< / targetId> 
< /依赖关系> 
  

有没有办法在不修改模型的情况下在JAXB注释中执行此操作？

  package forum7278406; 
 
 import javax.xml.bind.annotation.adapters.XmlAdapter; 
 
 public class TargetAdapter extends XmlAdapter< Long，Target> {
 
 @Override 
 public Long marshal（Target target）抛出异常{
 return target.getId（）; 
 
 $ b @Override 
 public target unmarshal（Long id）throws Exception {
 Target target = new Target（）; 
 target.setId（id）; 
回报目标; 
 
 
 $ b $ / code> 

使用 @XmlJavaTypeAdapter 注释在 Dependency 类中注册XmlAdapter ：

  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 
私人长ID; 
 
 @ManyToOne（可选= false）
 @Column（name =target_id）
 @XmlJavaTypeAdapter（TargetAdapter.class）
私有目标目标; 
 
 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; 
} 
 
} 
  





---

继续

而不是仅创建 Target 我们可以使用 EntityManager 从数据库中查询相应的实例。我们的 XmlAdapter 会被改为：



  package forum7278406; 
 
导入javax.persistence.EntityManager; 
 import javax.xml.bind.annotation.adapters.XmlAdapter; 
 
 public class TargetAdapter extends XmlAdapter< Long，Target> {
 
 EntityManager entityManager; 
 $ b $ public TargetAdapter（）{
} 
 
 public TargetAdapter（EntityManager entityManager）{
 this.entityManager = entityManager; 
} 
 
 @Override 
 public Long marshal（Target target）抛出异常{
 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）; 
} 
返回目标; 
} 
 
} 
  

现在设置 EntityManager 在我们的 XmlAdapter 上，我们可以做到以下几点：



  Unmarshaller umarshaller = jaxbContext.createUnmarshaller（）; 
 TargetAdapter targetAdatper = new TargetAdapter（entityManager）; 
 unmarshaller.setAdapter（targetAdapter）; 
  




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... */
}

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>

Is there a way to do this in JAXB annotations without modifying my model?

解决方案

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;
    }

}

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;
    }

}

---

Going Further

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;
    }

}

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);

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