我的问题的答案
让我进一步了解有关使用XmlSeeAlso，XmlElementReference以及JaxbContext.newInstance中涉及的类规范的问题的详细信息。
我开始尝试回答这个问题：
我在下面创建了Junit测试。为此，我来到了这里：
在这种状态下，代码可编译并运行 - 它会编组o.k.但不像预期的那样流氓。 元帅的结果是：
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Message>
<BasicInfo ref="id001"/>
</Message>
Unmarshalling不会像适配器中的代码那样创建BasicInfo：
public BasicInfo unmarshal(BasicInfoRef info) throws Exception {
BasicInfo binfo=new BasicInfo();
binfo.id=info.ref;
return binfo;
}
我发现这一切都非常令人困惑 - 事情似乎有些矛盾，而且大多数情况下并没有像我期望的那样对JaxB设置有所帮助。大多数组合不起作用，那些起作用的组合还没有给出完整的结果。我认为这也取决于所使用的版本和实现。
更新 经过考虑：
以下修改后的代码接近预期。
尝试时出现的错误是：
javax.xml.bind.MarshalException
- with linked exception:
[com.sun.istack.SAXException2: unable to marshal type "com.bitplan.storage.jaxb.TestRefId$BasicInfo$BasicInfoRef" as an element because it is missing an @XmlRootElement annotation]
at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:323)
这段代码有很多评论可以评论进出，以找出如果有人尝试会发生什么...... 我仍然不知道避免多余注释的最佳解决方案是什么。
修改后的代码：
package com.bitplan.storage.jaxb;
import static org.junit.Assert.*;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlSeeAlso;
import javax.xml.bind.annotation.adapters.XmlAdapter;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAccessType;
import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorNode;
import org.eclipse.persistence.oxm.annotations.XmlDiscriminatorValue;
import org.junit.Test;
/**
* Test the Reference/Id handling for Jaxb
*
* @author wf
*
*/
public class TestRefId {
@XmlDiscriminatorNode("@reforid")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlJavaTypeAdapter(RefOrId.Adapter.class)
public static class RefOrId {
@XmlAttribute(name = "reforid")
public String reforid;
public RefOrId() {
}
@XmlAttribute
public String id;
@XmlAttribute
public String ref;
public static class Adapter extends XmlAdapter<RefOrId, RefOrId> {
@Override
public RefOrId marshal(RefOrId idref) throws Exception {
if (idref == null)
return null;
System.out.println("marshalling " + idref.getClass().getSimpleName()
+ " reforid:" + idref.reforid);
if (idref instanceof Ref)
return new Id(((Ref) idref).ref);
return idref;
}
@Override
public RefOrId unmarshal(RefOrId idref) throws Exception {
System.out.println("unmarshalling " + idref.getClass().getSimpleName()
+ " reforid:" + idref.reforid);
return idref;
}
}
}
@XmlDiscriminatorValue("id")
@XmlAccessorType(XmlAccessType.FIELD)
public static class Id extends RefOrId {
public Id() {
reforid = "id";
}
public Id(String pId) {
this();
this.id = pId;
}
}
@XmlDiscriminatorValue("ref")
@XmlAccessorType(XmlAccessType.FIELD)
public static class Ref extends RefOrId {
public Ref() {
reforid = "ref";
}
public Ref(String pRef) {
this();
this.ref = pRef;
}
}
/*
* https://stackoverflow.com/questions/8292427/is-it-possible-to-xmlseealso-on-a
* -class-without-no-args-constructor-which-has
*/
@XmlRootElement(name = "BasicInfo")
public static class BasicInfo {
public BasicInfo() {
};
public BasicInfo(String pId, String pInfo) {
this.id = new Id(pId);
this.basic = pInfo;
}
// @XmlTransient
public RefOrId id;
public String basic;
}
@XmlRootElement(name = "SpecificInfoA")
// @XmlJavaTypeAdapter(BasicInfo.Adapter.class)
public static class SpecificInfoA extends BasicInfo {
public SpecificInfoA() {
};
public SpecificInfoA(String pId, String pInfo, String pInfoA) {
super(pId, pInfo);
infoA = pInfoA;
}
public String infoA;
}
@XmlRootElement(name = "Message")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({ SpecificInfoA.class, BasicInfo.class })
public static class Message {
public Message() {
};
public Message(BasicInfo pBasicInfo) {
basicInfos.add(pBasicInfo);
}
// @XmlJavaTypeAdapter(BasicInfo.Adapter.class)
// @XmlElement(name="basicInfo",type=BasicInfoRef.class)
@XmlElementWrapper(name = "infos")
@XmlElement(name = "info")
public List<BasicInfo> basicInfos = new ArrayList<BasicInfo>();
}
/**
* marshal the given message
*
* @param jaxbContext
* @param message
* @return - the xml string
* @throws JAXBException
*/
public String marshalMessage(JAXBContext jaxbContext, Message message)
throws JAXBException {
Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
// output pretty printed
jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
StringWriter sw = new StringWriter();
jaxbMarshaller.marshal(message, sw);
String xml = sw.toString();
return xml;
}
/**
* test marshalling and umarshalling a message
*
* @param message
* @throws JAXBException
*/
public void testMessage(Message message) throws JAXBException {
@SuppressWarnings("rawtypes")
Class[] classes = { Message.class, SpecificInfoA.class, BasicInfo.class }; // BasicInfo.class,};
// https://stackoverflow.com/questions/8318231/xmlseealso-alternative/8318490#8318490
// https://stackoverflow.com/questions/11966714/xmljavatypeadapter-not-being-detected
JAXBContext jaxbContext = JAXBContext.newInstance(classes);
String xml = marshalMessage(jaxbContext, message);
System.out.println(xml);
Unmarshaller u = jaxbContext.createUnmarshaller();
Message result = (Message) u.unmarshal(new StringReader(xml));
assertNotNull(result);
assertNotNull(message.basicInfos);
for (BasicInfo binfo : message.basicInfos) {
RefOrId id = binfo.id;
assertNotNull(id);
System.out.println("basicInfo-id " + id.getClass().getSimpleName()
+ " for reforid " + id.reforid);
// assertEquals(message.basicInfo.id, result.basicInfo.id);
}
xml = marshalMessage(jaxbContext, result);
System.out.println(xml);
}
/**
* switch Moxy
*
* @param on
* @throws IOException
*/
public void switchMoxy(boolean on) throws IOException {
File moxySwitch = new File(
"src/test/java/com/bitplan/storage/jaxb/jaxb.properties");
if (on) {
PrintWriter pw = new PrintWriter(new FileWriter(moxySwitch));
pw.println("javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory");
pw.close();
} else {
moxySwitch.delete();
}
}
@Test
public void testStackOverflow8292427() throws JAXBException, IOException {
boolean[] moxyOnList = { false };
for (boolean moxyOn : moxyOnList) {
switchMoxy(moxyOn);
System.out.println("Moxy used: " + moxyOn);
Message message = new Message(new BasicInfo("basicId001",
"basicValue for basic Info"));
message.basicInfos.add(new SpecificInfoA("specificId002",
"basicValue for specific Info", "specific info"));
message.basicInfos.add(new SpecificInfoA("specificId002",
"basicValue for specific Info", "specific info"));
testMessage(message);
}
}
}
这是上面提到的Junit测试（更新前）：
package com.bitplan.storage.jaxb;
import static org.junit.Assert.*;
import java.io.StringReader;
import java.io.StringWriter;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElementRef;
import javax.xml.bind.annotation.XmlElementRefs;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlSeeAlso;
import javax.xml.bind.annotation.adapters.XmlAdapter;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAccessType;
import org.junit.Test;
// Test the Reference/Id handling for Jaxb
public class TestRefId {
/*
* https://stackoverflow.com/questions/8292427/is-it-possible-to-xmlseealso-on-a-class-without-no-args-constructor-which-has
*/
@XmlRootElement(name="BasicInfo")
@XmlJavaTypeAdapter(BasicInfo.Adapter.class)
public static class BasicInfo {
@XmlRootElement(name="BasicInfo")
@XmlAccessorType(XmlAccessType.FIELD)
public static class BasicInfoRef {
@XmlAttribute(name = "ref")
public String ref;
}
public static class Adapter extends XmlAdapter<BasicInfoRef,BasicInfo>{
@Override
public BasicInfoRef marshal(BasicInfo info) throws Exception {
BasicInfoRef infoRef = new BasicInfoRef();
infoRef.ref=info.id;
return infoRef;
}
@Override
public BasicInfo unmarshal(BasicInfoRef info) throws Exception {
BasicInfo binfo=new BasicInfo();
binfo.id=info.ref;
return binfo;
}
} // Adapter
public String id;
public String basic;
}
@XmlJavaTypeAdapter(BasicInfo.Adapter.class)
public static class SpecificInfoA extends BasicInfo {
public String infoA;
}
@XmlRootElement(name="Message")
@XmlAccessorType(XmlAccessType.FIELD)
@XmlSeeAlso({SpecificInfoA.class,BasicInfo.class})
public static class Message {
// https://stackoverflow.com/questions/3107548/xmljavatypeadapter-w-inheritance
@XmlElementRefs({
@XmlElementRef(name="basic", type=BasicInfo.class),
// @XmlElementRef(name="infoA", type=SpecificInfoA.class)
})
public BasicInfo basicInfo;
}
@Test
public void testStackOverflow8292427() throws JAXBException {
Message message=new Message();
SpecificInfoA info=new SpecificInfoA();
info.id="id001";
info.basic="basicValue";
info.infoA="infoAValue";
message.basicInfo=info;
@SuppressWarnings("rawtypes")
Class[] classes= {Message.class,SpecificInfoA.class,BasicInfo.class,BasicInfo.BasicInfoRef.class}; // BasicInfo.class,};
// https://stackoverflow.com/questions/8318231/xmlseealso-alternative/8318490#8318490
JAXBContext jaxbContext = JAXBContext.newInstance(classes);
Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
// output pretty printed
jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
StringWriter sw = new StringWriter();
jaxbMarshaller.marshal(message, sw);
String xml=sw.toString();
System.out.println(xml);
Unmarshaller u = jaxbContext.createUnmarshaller();
Message result = (Message) u.unmarshal(new StringReader(xml));
assertNotNull(result);
assertNotNull("basicInfo should not be null",result.basicInfo);
assertEquals("id001",result.basicInfo.id);
}
}