如何在解组期间使用JAXB XmlAdapter处理XML IDREF的前向引用

Question

是否有可能在解组过程中处理JAXB XmlAdapter中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>

中guardian字段可以引用文档中其他地方的另一个Person类型元素。我目前在编组时使用XmlAdapter，以便在第一次编组对象时，它通过包含进行编组，并且该对象的任何后续事件都通过引用进行编组。看看我之前的问题。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元素出现之后。

这是可能的吗?还是我需要用不同的方式来处理?谢谢!

Answer 1

我对你的相关问题有一个答案，我概述了如何使用XmlAdapter来实现通过包含/嵌套编组对象的第一次出现和所有其他出现通过引用编组的用例:

• JAXB可以先通过包含封送，然后再通过@ xmldref封送用于后续引用吗?

选项1 - @XmlID/@XmlIDREF

如果你所有的Person对象都是通过嵌套来表示的，并且你想引入一些基于键的关系，那么你最好使用@XmlID将字段/属性标记为键，使用@XmlID将字段/属性映射为外键。您的Person类看起来像:

@XmlAccessorType(XmlAccessType.FIELD)
public class Person {
    @XmlID
    private String id;
    @XmlIDREF
    private Person guardian;
}

获取更多信息

• http://blog.bdoughan.com/2010/10/jaxb-and-shared-references-xmlid-and.html

选项#2 -使用XmlAdapter

如果您将XmlAdapter从我之前的答案更新为:

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;
    }
}

那么您将能够解组如下所示的XML文档，其中引用首先发生:

<?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>