JAXB最初可以通过收容进行封送，然后通过@XmlIDREF封送后续引用吗？ [英] Can JAXB marshal by containment at first then marshal by @XmlIDREF for subsequent references?

问题描述

我想知道是否可以对我的类进行注释，以便第一次编组遇到一个对象，它会生成一个相应类型的XML元素，但是任何其他任何后续对该对象的引用都将具有XML IDREF条目创建？

I'm wondering if it's possible to annotate my classes so that the first time the marshaller encounters an object, it generates an XML element of the appropriate type, but any subsequent reference to this object by anything else will have an XML IDREF entry created?

推荐答案

您可以利用JAXB的 XmlAdapter 的概念来执行以下操作：

You can leverage the concept of JAXB's XmlAdapter to do something like the following:

input.xml

以下是我将用于此示例的XML文档。第三个电话号码条目是对第一个电话号码条目的引用，以及第五个电话号码条目是对第4个的引用。

The following is the XML document I will use for this example. The 3rd phone-number entry is a reference to the 1st phone-number entry, and the 5th phone-number entry is a reference to the 4th.:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
    <phone-number id="A">
        <number>555-AAAA</number>
    </phone-number>
    <phone-number id="B">
        <number>555-BBBB</number>
    </phone-number>
    <phone-number id="A"/>
    <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>

客户

客户类维护一个 PhoneNumber 对象的集合。同一个PhoneNumber实例可能会在集合中多次出现。

The customer class maintains a collection of PhoneNumber objects. The same instance of PhoneNumber may appear multiple times in the collection.

package forum7587095;

import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Customer {

    private List<PhoneNumber> phoneNumbers;

    @XmlElement(name="phone-number")
    public List<PhoneNumber> getPhoneNumbers() {
        return phoneNumbers;
    }

    public void setPhoneNumbers(List<PhoneNumber> phoneNumbers) {
        this.phoneNumbers = phoneNumbers;
    }

}

PhoneNumber

这是一个可以出现在文档本身或作为参考的类。这将使用 XmlAdapter 进行处理。使用 @XmlJavaTypeAdapter 注释配置XmlAdapter。由于我们在类型/类级别指定了此适配器，因此它将应用于引用 PhoneNumber 类的所有属性：

This is a class that can either appear in the document itself or as a reference. This will be handled using an XmlAdapter. An XmlAdapter is configured using the @XmlJavaTypeAdapter annotation. Since we have specified this adapter at the type/class level it will apply to all properties referencing the PhoneNumber class:

package forum7587095;

import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlJavaTypeAdapter(PhoneNumberAdapter.class)
public class PhoneNumber {

    private String id;
    private String number;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    @Override
    public boolean equals(Object arg0) {
        if(null == arg0 || arg0.getClass() != this.getClass()) {
            return false;
        }
        PhoneNumber test = (PhoneNumber) arg0;
        if(!equals(id, test.getId())) {
            return false;
        }
        return equals(number, test.getNumber());
    }

    protected boolean equals(String control, String test) {
        if(null == control) {
            return null == test;
        } else {
            return control.equals(test);
        }
    }

    @Override
    public int hashCode() {
        return id.hashCode();
    }

}

WorkPhoneNumber

根据您的评论，我添加了 PhoneNumber 的子类。

Based on your comment I have added a subclass of PhoneNumber.

package forum7587095;

public class WorkPhoneNumber extends PhoneNumber {

    private String extension;

    public String getExtension() {
        return extension;
    }

    public void setExtension(String extension) {
        this.extension = extension;
    }

    @Override
    public boolean equals(Object arg0) {
        if(!super.equals(arg0)) {
            return false;
        }
        return equals(extension, ((WorkPhoneNumber) arg0).getExtension());
    }

}

PhoneNumberAdapter

以下是 XmlAdapter 的实现。请注意，如果之前看过PhoneNumber对象，我们必须维护。如果有，我们只填充 AdaptedPhoneNumber 对象的 id 部分。

Below is the implementation of the XmlAdapter. Note that we must maintain if the PhoneNumber object has been seen before. If it has we only populate the id portion of the AdaptedPhoneNumber object.

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) {
            return phoneNumber;
        }
        phoneNumber = adaptedPhoneNumber.getPhoneNumber();
        phoneNumberMap.put(phoneNumber.getId(), phoneNumber);
        return phoneNumber;
    }

}

演示

确保 XmlAdapter 的相同实例用于整个 marshal 和 unmarshal 操作我们必须在 Marshaller 和<上专门设置XmlAdapter的实例code> Unmarshaller ：

To ensure the same instance of the XmlAdapter is used for the entire marshal and unmarshal operations we must specifically set an instance of the XmlAdapter on both the Marshaller and Unmarshaller:

package forum7587095;

import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Customer.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        unmarshaller.setAdapter(new PhoneNumberAdapter());
        File xml = new File("src/forum7587095/input.xml");
        Customer customer = (Customer) unmarshaller.unmarshal(xml);

        System.out.println(customer.getPhoneNumbers().get(0) == customer.getPhoneNumbers().get(2));
        System.out.println(customer.getPhoneNumbers().get(3) == customer.getPhoneNumbers().get(4));

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setAdapter(new PhoneNumberAdapter());
        marshaller.marshal(customer, System.out);
    }

}

输出

true
true
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<customer>
    <phone-number id="A">
        <number>555-AAAA</number>
    </phone-number>
    <phone-number id="B">
        <number>555-BBBB</number>
    </phone-number>
    <phone-number id="A"/>
    <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>

更多信息

• http：//blog.bdoughan .com / 2011/09 / mixing-nesting-and-references-with.html


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


• http://blog.bdoughan.com/search/label/XmlAdapter


• http：//blog.bdoughan .com / 2010/11 / jaxb-and-inheritance-using-xsitype.html


• http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-using-substitution.html

• http://blog.bdoughan.com/2011/09/mixing-nesting-and-references-with.html
• http://blog.bdoughan.com/2010/10/jaxb-and-shared-references-xmlid-and.html
• http://blog.bdoughan.com/search/label/XmlAdapter
• http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-using-xsitype.html
• http://blog.bdoughan.com/2010/11/jaxb-and-inheritance-using-substitution.html

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