It seems JAXB can't read what it writes. Consider the following code:
JAXB似乎無法讀取它所寫的內容。考慮下面的代碼:
interface IFoo {
void jump();
}
@XmlRootElement
class Bar implements IFoo {
@XmlElement
public String y;
public Bar() {
y = "";
}
public Bar(String y) {
this.y = y;
}
@Override
public void jump() {
System.out.println(y);
}
}
@XmlRootElement
class Baz implements IFoo {
@XmlElement
public int x;
public Baz() {
x = 0;
}
public Baz(int x) {
this.x = x;
}
@Override
public void jump() {
System.out.println(x);
}
}
@XmlRootElement
public class Holder {
private List<IFoo> things;
public Holder() {
things = new ArrayList<>();
}
@XmlElementWrapper
@XmlAnyElement
public List<IFoo> getThings() {
return things;
}
public void addThing(IFoo thing) {
things.add(thing);
}
}
// ...
try {
JAXBContext context = JAXBContext.newInstance(Holder.class, Bar.class, Baz.class);
Holder holder = new Holder();
holder.addThing(new Bar("1"));
holder.addThing(new Baz(2));
holder.addThing(new Baz(3));
for (IFoo thing : holder.getThings()) {
thing.jump();
}
StringWriter s = new StringWriter();
context.createMarshaller().marshal(holder, s);
String data = s.toString();
System.out.println(data);
StringReader t = new StringReader(data);
Holder holder2 = (Holder)context.createUnmarshaller().unmarshal(t);
for (IFoo thing : holder2.getThings()) {
thing.jump();
}
}
catch (Exception e) {
System.err.println(e.getMessage());
}
It's a simplified example, of course. The point is that I have to store two very differently implemented classes, Bar and Baz, in one collection. Well, I observed that they have pretty similar public interface, so I created an interface IFoo and made them two to implement it. Now, I want to have tools to save and load this collection to/from XML. Unfortunately, this code doesn't quite work: the collection is saved, but then it cannot be loaded! The intended output is
當然,這是一個簡化的例子。重點是,我必須在一個集合中存儲兩個非常不同的實現類,Bar和Baz。我觀察到它們有非常相似的公共接口,所以我創建了一個接口IFoo,並讓它們兩個來實現它。現在,我想要一些工具來保存和加載這個集合到/從XML。不幸的是,這段代碼不能正常工作:保存了集合,但是不能加載它!預期的輸出
1
2
3
some xml
1
2
3
But unfortunately, the actual output is
但不幸的是,實際輸出是
1
2
3
some xml
com.sun.org.apache.xerces.internal.dom.ElementNSImpl cannot be cast to testapplication1.IFoo
Apparently, I need to use the annotations in a different way? Or to give up on JAXB and look for something else? I, well, can write "XMLNode toXML()" method for all classes I wan't to (de)marshal, but...
顯然,我需要以不同的方式使用注釋?或者放棄JAXB,尋找其他東西?我可以為我不想編組的所有類編寫“XMLNode toXML()”方法,但是…
8
Try the following @XmlAnyElement(lax=true)
. The lax
flag tells the JAXB (JSR-222) implementation to match elements to domain objects based their @XmlRootElement
and @XmlElementDecl
annotations. Without it the contents are treated as DOM nodes.
試試以下@XmlAnyElement(寬松= true)。lax標志告訴JAXB (JSR-222)實現根據其@XmlRootElement和@XmlElementDecl注釋將元素匹配到域對象。沒有它,內容將被視為DOM節點。
@XmlRootElement
public class Holder {
private List<IFoo> things;
public Holder() {
things = new ArrayList<>();
}
@XmlElementWrapper
@XmlAnyElement(lax=true)
public List<IFoo> getThings() {
return things;
}
public void addThing(IFoo thing) {
things.add(thing);
}
}
For More Information
的更多信息
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