(moxy) jaxb 编组和休眠代理对象 [英] (moxy) jaxb marshaling and hibernate proxy objects
问题描述
在过去的几天里，我尝试使用 MOXy JAXB 支持 Hibernate 模型的 XML 编组/解组.尝试这样做时，我遇到了休眠代理对象的问题.考虑类似的事情:
In the last couple of days I have tried to make support for XML marshalling/unmarshalling of a Hibernate model, using MOXy JAXB. Trying to do this, I have run into a problem with hibernates proxy objects. Consider something like:
public class User {
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "address")
public Address getAddress() {
return address;
}
}
public abstract class Address {
// Something
}
public class CoolAddress extends Address {
public String getSomething() {
return something;
}
}
我尝试使用 MOXy JAXB 通过以下方式映射此代码:
I have tried to map this code using MOXy JAXB in the following way:
@XmlAccessorType(XmlAccessType.NONE)
public class User {
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "address")
@XmlElement
public Address getAddress() {
return address;
}
}
@XmlAccessorType(XmlAccessType.NONE)
@XmlSeeAlso(CoolAddress.class)
public abstract class Address {
// Something
}
@XmlAccessorType(XmlAccessType.NONE)
public class CoolAddress extends Address {
@XmlElement
public String getSomething() {
return something;
}
}
我的问题是休眠实例化了通过在用户上调用 getAddress() 获得的地址的代理对象.然后，当 JAXB 尝试封送对象时，它无法发现它实际上是它正在尝试封送的 CoolAddress，这导致 CoolAddress 中的属性没有被封送.
My problem is that hibernate instantiates a proxy object of the address obtained by calling getAddress() on a User. Then, when JAXB tries to marshal the object, it can't find out that it actually is a CoolAddress it is trying to marshal, which results in that properties in CoolAddress not being marshaled.
我已经搜索/考虑了以下可能的解决方案:
I have googled/considered the following possible solutions:
- 以某种方式从 JAXB 获得回调，允许我将正在编组的对象替换为另一个对象.这将允许我从代理获取真实对象.
- 触摸模型中的所有对象，这将使休眠获取真实对象.除了手动运行所有非瞬态属性之外，我还没有找到任何聪明的方法，这很乏味.
- 设置休眠以在我正在编组模型的会话中使用急切获取.
我正在寻找替代建议，或者是否可以(并且容易)实施上述建议之一.任何帮助表示赞赏:).
I'm looking for alternative suggestions, or if one of the above suggestions is possible (and easy) to implement. Any help is appreciated :).
推荐答案
要解决这个 Hibernate 问题，您可以使用 XmlAdapter.XmlAdapter 看起来类似于 marshal 方法中的逻辑是从代理转换为真实对象:
To solve this Hibernate issue you may be able to use an XmlAdapter. The XmlAdapter would look something like where the logic in the marshal method is to convert from the proxy to the real object:
package forum6838323;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public class AddressAdapter extends XmlAdapter<Address, Address> {
@Override
public Address unmarshal(Address v) throws Exception {
return v;
}
@Override
public Address marshal(Address v) throws Exception {
// TODO Auto-generated method stub
return null;
}
}
您配置 XmlAdapter 如下:
public class User {
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "address")
@XmlJavaTypeAdapter(AddressAdapter.class)
public Address getAddress() {
return address;
}
}
如果您需要将初始化的 XmlAdapter 传递给 JAXB 编组器，您也可以这样做，请参阅以下示例:
If you need to pass an initialized XmlAdapter to the JAXB marshaller, you can do that as well, see the following for an example:
使用 EclipseLink JPA 的替代方法
注意:EclipseLink JPA 中的延迟加载不会导致此问题:
Note: The lazy loading in EclipseLink JPA does not cause this issue:
用户
package forum6838323;
import javax.persistence.*;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;
@Entity
@Table(name="users")
@XmlRootElement
public class User {
private int id;
Address address;
@Id
@XmlAttribute
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "address")
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}
地址
package forum6838323;
import javax.persistence.*;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlSeeAlso;
@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="TYPE", discriminatorType=DiscriminatorType.STRING)
@DiscriminatorValue("ADDRESS")
@XmlSeeAlso(CoolAddress.class)
public class Address {
private int id;
private String street;
@Id
@XmlAttribute
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
}
酷地址
package forum6838323;
import javax.persistence.*;
@Entity
@DiscriminatorValue("COOL")
public class CoolAddress extends Address {
private String something;
public String getSomething() {
return something;
}
public void setSomething(String something) {
this.something = something;
}
}
演示
package forum6838323;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
public class Demo {
public static void main(String[] args) throws Exception {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("Forum6838323");
EntityManager em = emf.createEntityManager();
User user = em.find(User.class, 2);
System.out.println("user.address BEFORE marshal: " + user.address);
JAXBContext jc = JAXBContext.newInstance(User.class);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(user, System.out);
System.out.println("user.address AFTER marshal: " + user.address);
}
}
输出
您可以从输出中看到地址值正在被延迟加载，因为该字段在封送之前为空，之后填充:
You can see from the output that the address value is being lazily loaded since the field is null before the marshal and populated afterwards:
user.address BEFORE marshal: null
[EL Finest]: 2011-07-27 11:47:13.118--ServerSession(23503403)--Thread(Thread[main,5,main])--Execute query ReadObjectQuery(name="Forum6838323" referenceClass=Address )
[EL Finest]: 2011-07-27 11:47:13.118--ServerSession(23503403)--Connection(10272075)--Thread(Thread[main,5,main])--Connection acquired from connection pool [default].
[EL Fine]: 2011-07-27 11:47:13.118--ServerSession(23503403)--Connection(10272075)--Thread(Thread[main,5,main])--SELECT ID, TYPE, STREET, SOMETHING FROM ADDRESS WHERE (ID = ?)
bind => [2]
[EL Finest]: 2011-07-27 11:47:13.118--ServerSession(23503403)--Connection(10272075)--Thread(Thread[main,5,main])--Connection released to connection pool [default].
[EL Finest]: 2011-07-27 11:47:13.118--UnitOfWork(6131844)--Thread(Thread[main,5,main])--Register the existing object forum6838323.CoolAddress@109ea96
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<user id="2">
<address xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="coolAddress" id="2">
<street>2 B Road</street>
<something>Cool Road</something>
</address>
</user>
user.address AFTER marshal: forum6838323.CoolAddress@83b1b
这篇关于(moxy) jaxb 编组和休眠代理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！
