如何在unmarshal期间使用JAXB XmlAdapter处理XML IDREF的前向引用？

在解组过程中是否可以在JAXB XmlAdapter中处理XML IDREF元素的前向引用？例如,我有以下XML complexType：

<xs:complexType name="person">
    <xs:complexContent>
        <xs:sequence>
            <xs:element name="dateOfBirth" type="xs:dateTime" minOccurs="0"/>
            <xs:element name="firstName" type="xs:string" minOccurs="0"/>
            <xs:element name="gender" type="xs:string" minOccurs="0"/>
            <xs:element name="guardian" type="xs:IDREF" minOccurs="0"/>
            <xs:element name="homePhone" type="xs:string" minOccurs="0"/>
            <xs:element name="lastName" type="xs:string" minOccurs="0"/>
        </xs:sequence>
    </xs:complexContent>
</xs:complexType>

监护人字段可以在文档中的其他位置引用另一个Person类型元素.我正在编组时使用XmlAdapter,以便第一次对象进行编组时,它会被包含编组,并且此对象的任何后续出现都将通过引用进行编组.请参阅上一个mine的问题.但是,由于我的XML实例文档的创建方式,Person元素的第一次出现可能发生在IDREF发生之后.

这是可能的吗？或者我需要以不同的方式处理这个问题？谢谢！

我对你的 related question有一个答案我概述了如何使用XmlAdapter来实现一个用例,其中第一次出现的对象是通过包含/嵌套编组的,所有其他出现都是通过引用编组的：

> Can JAXB marshal by containment at first then marshal by @XmlIDREF for subsequent references?

选项#1 – @ XmlID / @ XmlIDREF

如果您的所有Person对象都通过嵌套表示,并且您想要引入一些基于键的关系,那么您最好使用@XmlID将字段/属性标记为键,将@XmlID用于将字段/属性标记为外部键.您的Person类看起来像：

@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    @XmlID
    private String id;

    @XmlIDREF
    private Person guardian;
}

选项#2 – 使用XmlAdapter

如果您将我的previous answer中的XmlAdapter更新为：

package forum7587095;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlSeeAlso;
import javax.xml.bind.annotation.XmlType;
import javax.xml.bind.annotation.adapters.XmlAdapter;

public class PhoneNumberAdapter extends XmlAdapter<PhoneNumberAdapter.AdaptedPhoneNumber,PhoneNumber>{

    private List<PhoneNumber> phoneNumberList = new ArrayList<PhoneNumber>();
    private Map<String,PhoneNumber> phoneNumberMap = new HashMap<String,PhoneNumber>();

    @XmlSeeAlso(AdaptedWorkPhoneNumber.class)
    @XmlType(name="phone-number")
    public static class AdaptedPhoneNumber {
        @XmlAttribute public String id;
        public String number;

        public AdaptedPhoneNumber() {
        }

        public AdaptedPhoneNumber(PhoneNumber phoneNumber) {
            id = phoneNumber.getId();
            number = phoneNumber.getNumber();
        }

        public PhoneNumber getPhoneNumber() {
            PhoneNumber phoneNumber = new PhoneNumber();
            phoneNumber.setId(id);
            phoneNumber.setNumber(number);
            return phoneNumber;
        }

    }

    @XmlType(name="work-phone-number")
    public static class AdaptedWorkPhoneNumber extends AdaptedPhoneNumber {

        public String extension;

        public AdaptedWorkPhoneNumber() {
        }

        public AdaptedWorkPhoneNumber(WorkPhoneNumber workPhoneNumber) {
            super(workPhoneNumber);
            extension = workPhoneNumber.getExtension();
        }

        @Override
        public WorkPhoneNumber getPhoneNumber() {
            WorkPhoneNumber phoneNumber = new WorkPhoneNumber();
            phoneNumber.setId(id);
            phoneNumber.setNumber(number);
            phoneNumber.setExtension(extension);
            return phoneNumber;
        }
}

    @Override
    public AdaptedPhoneNumber marshal(PhoneNumber phoneNumber) throws Exception {
        AdaptedPhoneNumber adaptedPhoneNumber;
        if(phoneNumberList.contains(phoneNumber)) {
            if(phoneNumber instanceof WorkPhoneNumber) {
                adaptedPhoneNumber = new AdaptedWorkPhoneNumber();
            } else {
                adaptedPhoneNumber = new AdaptedPhoneNumber();
            }
            adaptedPhoneNumber.id = phoneNumber.getId();
        } else {
            if(phoneNumber instanceof WorkPhoneNumber) {
                adaptedPhoneNumber = new AdaptedWorkPhoneNumber((WorkPhoneNumber)phoneNumber);
            } else {
                adaptedPhoneNumber = new AdaptedPhoneNumber(phoneNumber);
            }
            phoneNumberList.add(phoneNumber);
        }
        return adaptedPhoneNumber;
    }

    @Override
    public PhoneNumber unmarshal(AdaptedPhoneNumber adaptedPhoneNumber) throws Exception {
        PhoneNumber phoneNumber = phoneNumberMap.get(adaptedPhoneNumber.id);
        if(null != phoneNumber) {
            if(adaptedPhoneNumber.number != null) {
                phoneNumber.setNumber(adaptedPhoneNumber.number);
            }
            return phoneNumber;
        }
        phoneNumber = adaptedPhoneNumber.getPhoneNumber();
        phoneNumberMap.put(phoneNumber.getId(),phoneNumber);
        return phoneNumber;
    }

}

然后,您将能够解组首先出现引用的XML文档：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
    <phone-number id="A"/>
    <phone-number id="B">
        <number>555-BBBB</number>
    </phone-number>
    <phone-number id="A">
        <number>555-AAAA</number>
    </phone-number>
    <phone-number xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="work-phone-number" id="W">
        <number>555-WORK</number>
        <extension>1234</extension>
    </phone-number>
    <phone-number xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="work-phone-number" id="W"/>
</customer>

如何在unmarshal期间使用JAXB XmlAdapter处理XML IDREF的前向引用？

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