I've attempted to serialize several classes with the Collection interface as an attribute. It appears that this produces an invalid JSON string. Here's an example of the output I'm getting:

{"TestCollection": {
  "strings": [ "class" :"list""
    "String1"
  ]
}}

Notice the extra quote after list, for example. Also, here is the code I'm using to produce this output.

import java.util.ArrayList;
import java.util.Collection;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.json.JsonHierarchicalStreamDriver;

public class TestCollection {
private Collection strings;
public Collection getStrings() {
return strings;
}
public void setStrings(Collection strings) {
this.strings = strings;
}
public static void main(String[] args){
TestCollection test = new TestCollection();
ArrayList strings = new ArrayList();
strings.add("String1");
test.setStrings(strings);
XStream xs = new XStream(new JsonHierarchicalStreamDriver());
String xml = xs.toXML(test);
System.out.println(xml);
}
}