（MOXY）JAXB編組和休眠代理對象

Question

在過去幾天我試圖使一個休眠模式的XML編組/解組的支持，使用莫西JAXB。試圖做到這一點，我遇到了休眠代理對象的問題。 考慮是這樣的：

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; 
    } 
} 

我試圖映射以下列方式使用莫西JAXB驗證碼：

@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; 
    } 
} 

我的問題是，Hibernate的實例調用的getAddress獲得的地址的代理對象（）在用戶。然後，當JAXB試圖編組對象，它不能發現，它實際上是一個CoolAddress它試圖元帥，這導致在CoolAddress性能沒有被編。

我用Google搜索/考慮以下可能的解決方案：

• 在某種意義上，從JAXB得到一個回調，讓我來代替被編爲另一個對象。這將允許我從代理中獲取真實對象。
• 觸摸模型，這將使​​休眠獲取真實對象的所有對象。除了手動運行所有非瞬態屬性之外，我一直無法找到任何明智的方法，這很安靜。
• 設置休眠使用預先抓取會話我編組模型。

我正在尋找替代建議，或者如果上述建議之一是可能（和容易）實施。任何幫助表示讚賞:)。

Answer 1

爲了解決這個問題Hibernate的問題，你可能能夠使用XmlAdapter。該XmlAdapter看起來像其中元帥方法的邏輯是從代理轉換爲真正的對象：

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; 
    } 
} 

如果你需要傳遞初始化的XmlAdapter到JAXB編組，你可以做到這一點爲好，見一個例子如下：

• Using JAXB to cross reference XmlIDs from two XML files

---

替代使用的EclipseLink JPA

注：懶加載中的EclipseLink JPA不會導致此問題：

用戶

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; 
    } 

} 

CoolAddress

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); 
    } 

} 

輸出

您可以從輸出中看到，地址VAL由於該字段在元帥之前爲零，並且之後被填充，所以ue被延遲加載：

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