我想知道是否可以注释我的类，以便编码程序第一次遇到对象时，它会生成适当类型的XML元素，但是其他任何对该对象的后续引用都会创建XML IDREF条目吗？
最佳答案
您可以利用JAXB的XmlAdapter的概念执行以下操作:
input.xml
以下是本示例将使用的XML文档。第3个phone-number条目是对第1个phone-number条目的引用，第5个phone-number条目是对第4个条目的引用:
<?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
PhoneNumber对象的集合。同一PhoneNumber实例在集合中可能出现多次。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;
}
}
电话号码
这是一个类，可以显示在文档本身中，也可以作为引用。这将使用
XmlAdapter处理。 XmlAdapter使用@XmlJavaTypeAdapter批注进行配置。由于我们已经在类型/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: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();
}
}
工作电话号码
根据您的评论，我添加了
PhoneNumber的子类。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());
}
}
电话号码适配器
以下是
XmlAdapter的实现。请注意，如果以前已经看到过PhoneNumber对象，我们必须进行维护。如果有的话，我们只填充id对象的AdaptedPhoneNumber部分。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
为了确保整个
XmlAdapter和marshal操作都使用相同的unmarshal实例，我们必须在Marshaller和Unmarshaller上都专门设置XmlAdapter的实例: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>
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