Question

在过去的几天里，我尝试使用MOXy JAXB来支持Hibernate模型的XML编组/解组。试图这样做，我遇到了hibernates代理对象的问题。考虑类似的事情：

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以下列方式映射此代码：

@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hibernate实例化通过在User上调用getAddress（）获得的地址的代理对象。然后，当JAXB试图封送该对象时，它无法发现它实际上是一个正在尝试封送的CoolAddress，这导致CoolAddress中的属性没有被封送。

我用google搜索/考虑了以下可能的解决方案：

以某种方式从JAXB获取回调，允许我将被封送的对象替换为另一个。这将允许我从代理中获取真实对象。
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，这是非常繁琐的。
设置休眠以在会话中使用急切提取我正在整理模型。

我正在寻找其他建议，或者上述建议之一是否可行（并且易于实施）。任何帮助表示赞赏:)。

Answer 1

要解决此Hibernate问题，您可以使用XmlAdapter。 XmlAdapter看起来就像marshal方法中的逻辑从代理转换为真实对象的地方：

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;
    }

}

您可以按如下方式配置XmlAdapter：

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：

Using JAXB to cross reference XmlIDs from two XML files

替代使用EclipseLink JPA

注意：EclipseLink JPA中的延迟加载不会导致此问题：

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; } }

<强>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; } }

<强> 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; } }

<强>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); } }

<强>输出

您可以从输出中看到地址值被延迟加载，因为该字段在编组之前为空并在之后填充：

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

（moxy）jaxb编组和hibernate代理对象

1 个答案: