XStream arrayList to and from XML

Question

I do not know where the problem is at the moment. First time using xml, and I got some problems with putting ArrayList in xml file and taking it from it.

I was found this and I tried to do it same way: How to convert List of Object to XML doc using XStream

but unfortunately I failed. Here what I have so far: Class that holds ArrayList:

public class ElbowList{

private ArrayList<Elbow> elbows = new ArrayList<>();

public ElbowList(){
    elbows = new ArrayList<Elbow>();
}

public void setElbows(ArrayList<Elbow> elbows){
    this.elbows.clear();
    this.elbows = elbows;
}

public ArrayList<Elbow> getElbows() {
    return elbows;
}

public void add(Elbow elbow){
    elbows.add(elbow);
}
}

Save to XML:

MainFrame mainFrame = (MainFrame) SwingUtilities.getWindowAncestor(SetupPanel.this);
            ElbowList elbowList = (ElbowList) mainFrame.getObjects().get(2); //get ElbowList object
            XStream xstream = new XStream();
            xstream.alias("elbow", Elbow.class);
            xstream.alias("elbows", ElbowList.class);
            xstream.addImplicitCollection(ElbowList.class, "elbows", Elbow.class);

            String xml = xstream.toXML(elbowList.getElbows());
            System.out.println(xml);

            try {
                PrintWriter out = new PrintWriter("Save.xml");
                out.println(xml);
                out.close();
            } catch (FileNotFoundException ex) {
                Logger.getLogger(SetupPanel.class.getName()).log(Level.SEVERE, null, ex);
            }

And that one above actually seems to work correctly. Load XML file, there is where I got an exception call:

try {
                XStream xstream = new XStream();
                FileReader reader = new FileReader("Save.xml");

                MainFrame mainFrame = (MainFrame) SwingUtilities.getWindowAncestor(SetupPanel.this);
                ElbowList elbowList = (ElbowList) mainFrame.getObjects().get(2);
                elbowList.setElbows((ArrayList<Elbow>) xstream.fromXML(reader));//exception occurs here

                SpacePanel spacePanel = (SpacePanel) mainFrame.getObjects().get(1);
                spacePanel.repaint();

            } catch (IOException ex) {
                Logger.getLogger(SetupPanel.class.getName()).log(Level.SEVERE, null, ex);
            }

An exception I get:

Exception in thread "AWT-EventQueue-0" com.thoughtworks.xstream.converters.ConversionException: elbow : elbow
---- Debugging information ----
message             : elbow
cause-exception     : com.thoughtworks.xstream.mapper.CannotResolveClassException
cause-message       : elbow
class               : java.util.ArrayList
required-type       : java.util.ArrayList
converter-type      : com.thoughtworks.xstream.converters.collections.CollectionConverter
path                : /list/elbow
line number         : 2
version             : 1.4.7
-------------------------------
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:50)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:134)
    at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:32)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1185)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1169)
    at com.thoughtworks.xstream.XStream.fromXML(XStream.java:1040)
    at view.SetupPanel$2.actionPerformed(SetupPanel.java:78)
(...)

I dont get why there is an conversion exception, for me everything seems right if it comes to this line when exception occurs. I have no more ideas whats wrong, please help.

Answer 1

You forgot to add

XStream xstream = new XStream();
xstream.alias("elbow", Elbow.class);
xstream.alias("elbows", ElbowList.class);
xstream.addImplicitCollection(ElbowList.class, "elbows", Elbow.class);

too, when loading.