JAXB Configuration was broken by upgrading from JDK 1.7 to JDK 1.8 u05 for collections

Question

The code below used to work under the JAXB implementation used by JDK 1.7, but now under JDK 1.8 it's broken. In the code below you will find the key change that seems to make it work in 1.8. The "fix" under 1.8 is not really a fix because it's bad practice to expose internal collections for direct modification by the outside world. I want to control access to the internal list through my class and I don't want to complicate things by making observable collections and listening to them. This is not acceptable.

Is there any way to get my original code to work under the JAXB of JD 1.8?

 @XmlElementWrapper(name = "Wrap")
   @XmlElement(name = "Item", required = true)
   public synchronized void setList(List<CustomObject> values) {
     list.clear();
     list.addAll(values);
   }

public synchronized List<CustomObject> getList() {
//      return new ArrayList(list); // this was the original code that worked under 1.7
      return list; //this is the only thing that works under 1.8
   }

After more analysis, the problem seems to be coming from JAXB not calling the setter method for collections anymore (it used to under JDK 1.7). Now under JDK 1.8, it calls the getter and modifies the collection directly. This poses several problems:

1-forces the user to expose an internal collection to the outside world for free modification (bad practice) 2-doesn't allow the user to do any custom code when the list changes (such as what you could do if the setter was called). It might be possible to make an observable collection and listen to it, but this is a much more complicated workaround than just calling the setter method.

Answer 1

Background

When a collection property is mapped in JAXB it first checks the getter to see if the collection property has been pre-initialized. In the example below I want to have my property exposed as List<String>, but have the backing implementation be a LinkedList ready to hold 1000 items.

private List<String> foos = new LinkedList<String>(1000);

@XmlElement(name="foo")
public List<String> getFoos() {
    return foos;
}

Why Your Code Used to Work

If you previously had JAXB call the setter on a property mapped to a collection that returned a non-null response from the getter, then there was a bug in that JAXB implementation. Your code should not have worked in the previous version either.

How to Get the Setter Called

To have the setter called you just need to have your getter return null, on a new instance of the object. Your code could look something like:

import java.util.*;
import javax.xml.bind.annotation.*;

@XmlRootElement(name = "Foo")
public class Foo {

    private List<CustomObject> list = null;

    @XmlElementWrapper(name = "Wrap")
    @XmlElement(name = "Item", required = true)
    public synchronized void setList(List<CustomObject> values) {
        if (null == list) {
            list = new ArrayList<CustomObject>();
        } else {
            list.clear();
        }
        list.addAll(values);
    }

    public synchronized List<CustomObject> getList() {
        if (null == list) {
            return null;
        }
        return new ArrayList(list);
    }

}

---

UPDATE

If you don't need to perform any logic on the List returned from JAXB's unmarshalling then using field access may be an acceptable solution.

@XmlRootElement(name = "Foo")
@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {

    @XmlElementWrapper(name = "Wrap")
    @XmlElement(name = "Item", required = true)
    private List<CustomObject> list = null;

    public synchronized void setList(List<CustomObject> values) {
        if(null == list) {
            list = new ArrayList<CustomObject>();
        } else {
            list.clear();
        }
        list.addAll(values);
    }

    public synchronized List<CustomObject> getList() {
        return new ArrayList(list);
    }

}