Fails to internalize ObservableList

[MichaelEllis]

Starting with a simple class for a person

package xstreamfxextensions;

import com.thoughtworks.xstream.annotations.XStreamAlias;
import com.thoughtworks.xstream.annotations.XStreamImplicit;
import javafx.beans.property.IntegerProperty;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;

@XStreamAlias("Person")   //define class level alias
public class Person {

    @XStreamAlias("Sex")
    public enum Sex {

        MALE, FEMALE, UNKNOWN, OTHER
    };

    public StringProperty name = new SimpleStringProperty(this, "name", "nameless");
    public IntegerProperty age = new SimpleIntegerProperty(this, "age", 0);
    public ObjectProperty<Sex> sex = new SimpleObjectProperty<>(this, "sex", Sex.MALE);

    public ObservableList<Person> children  = FXCollections.<Person>observableArrayList();

    public Person(String name, int age, Sex sex) {
        this.name.set(name);
        this.age.set(age);
        this.sex.set(sex);
    }

    @Override
    public String toString() {
        return "Person{"
                + "name=" + name.get()
                + ", age=" + age.get()
                + ", sex=" + sex.get()
                + ", children=" + children
                + '}';
    }

}

A simple test class to use XStream and XStreamFX to externalise and internalise some people.

package xstreamfxextensions;

import com.dooapp.xstreamfx.FXConverters;
import com.sun.javafx.collections.ObservableListWrapper;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.io.xml.StaxDriver;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import javafx.beans.property.SimpleBooleanProperty;
import javafx.beans.property.SimpleFloatProperty;
import javafx.beans.property.SimpleIntegerProperty;
import javafx.beans.property.SimpleListProperty;
import javafx.beans.property.SimpleLongProperty;
import javafx.beans.property.SimpleMapProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.property.SimpleSetProperty;
import javafx.beans.property.SimpleStringProperty;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.sax.SAXSource;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.stream.StreamResult;
import org.junit.Test;
import org.xml.sax.InputSource;
import xstreamfxextensions.Person.Sex;

public class XStreamFXExtensionsTest {

    /**
     * Add XStream aliases for common JavaFX types
     *
     * @param xstream
     */
    public static void addFXAliases(XStream xstream) {
        Class[] cs = new Class[]{
            ObservableListWrapper.class,

            // The Simple... properties
            SimpleStringProperty.class,
            SimpleIntegerProperty.class,
            SimpleObjectProperty.class,
            SimpleFloatProperty.class,
            SimpleBooleanProperty.class,
            SimpleListProperty.class,
            SimpleLongProperty.class,
            SimpleMapProperty.class,
            SimpleSetProperty.class,
            SimpleFloatProperty.class,};

        for (Class c : cs) { // 
            // Alias the class's simple name to its pull name
            xstream.alias(c.getSimpleName(), c);
        }
    }

    @Test
    public void testSXtreamPerson() throws IOException {
        XStream xstream = new XStream(new StaxDriver());
        Person fred = new Person("Fred", 71, Sex.MALE);
        fred.children.add(new Person("Paul", 21, Sex.MALE));
        fred.children.add(new Person("James", 20, Sex.MALE));
        fred.children.add(new Person("Angela", 20, Sex.FEMALE));

        xstream.autodetectAnnotations(true);
        FXConverters.configure(xstream);
        addFXAliases(xstream);

        //Object to XML Conversion
        String xml = formatXml(xstream.toXML(fred));
        Files.write(Paths.get("PeopleImplicit.xml"), xml.getBytes());

        //XML to Object Conversion
        Person a = (Person) xstream.fromXML(xml);
        System.out.println(a);
    }

    public static String formatXml(String xml) {
        try {
            Transformer serializer = SAXTransformerFactory.newInstance().newTransformer();
            serializer.setOutputProperty(OutputKeys.INDENT, "yes");
            serializer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
            Source xmlSource = new SAXSource(new InputSource(new ByteArrayInputStream(xml.getBytes())));
            StreamResult res = new StreamResult(new ByteArrayOutputStream());
            serializer.transform(xmlSource, res);
            return new String(((ByteArrayOutputStream) res.getOutputStream()).toByteArray());
        } catch (Exception e) {
            return xml;
        }
    }

}

Running this results in error:

Testcase: testSXtreamPerson(xstreamfxextensions.XStreamFXExtensionsTest):   Caused an ERROR
Cannot instantiate com.sun.javafx.collections.ObservableListWrapper : com.sun.javafx.collections.ObservableListWrapper
---- Debugging information ----
message             : Cannot instantiate com.sun.javafx.collections.ObservableListWrapper
cause-exception     : java.lang.InstantiationException
cause-message       : com.sun.javafx.collections.ObservableListWrapper
class               : com.sun.javafx.collections.ObservableListWrapper
required-type       : com.sun.javafx.collections.ObservableListWrapper
converter-type      : com.dooapp.xstreamfx.ObservableListConverter
path                : /Person/children
line number         : 5
class[1]            : xstreamfxextensions.Person
converter-type[1]   : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
version             : 1.4.8
-------------------------------
com.thoughtworks.xstream.converters.ConversionException: Cannot instantiate com.sun.javafx.collections.ObservableListWrapper : com.sun.javafx.collections.ObservableListWrapper
---- Debugging information ----
message             : Cannot instantiate com.sun.javafx.collections.ObservableListWrapper
cause-exception     : java.lang.InstantiationException
cause-message       : com.sun.javafx.collections.ObservableListWrapper
class               : com.sun.javafx.collections.ObservableListWrapper
required-type       : com.sun.javafx.collections.ObservableListWrapper
converter-type      : com.dooapp.xstreamfx.ObservableListConverter
path                : /Person/children
line number         : 5
class[1]            : xstreamfxextensions.Person
converter-type[1]   : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
version             : 1.4.8
-------------------------------
    at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.createCollection(AbstractCollectionConverter.java:79)
    at com.thoughtworks.xstream.converters.collections.CollectionConverter.createCollection(CollectionConverter.java:103)
    at com.dooapp.xstreamfx.ObservableListConverter.createCollection(ObservableListConverter.java:40)
    at com.thoughtworks.xstream.converters.collections.CollectionConverter.unmarshal(CollectionConverter.java:79)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:66)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshallField(AbstractReflectionConverter.java:480)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:412)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.unmarshal(AbstractReflectionConverter.java:263)
    at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
    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:1206)
    at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:1190)
    at com.thoughtworks.xstream.XStream.fromXML(XStream.java:1061)
    at com.thoughtworks.xstream.XStream.fromXML(XStream.java:1052)
    at xstreamfxextensions.XStreamFXExtensionsTest.testSXtreamPerson(XStreamFXExtensionsTest.java:77)
Caused by: java.lang.InstantiationException: com.sun.javafx.collections.ObservableListWrapper
    at java.lang.Class.newInstance(Class.java:427)
    at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.createCollection(AbstractCollectionConverter.java:77)
Caused by: java.lang.NoSuchMethodException: com.sun.javafx.collections.ObservableListWrapper.<init>()
    at java.lang.Class.getConstructor0(Class.java:3082)
    at java.lang.Class.newInstance(Class.java:412)

I found modifying ObservableListConverter to

package com.dooapp.xstreamfx;

import com.sun.javafx.collections.ObservableListWrapper;
import com.thoughtworks.xstream.converters.Converter;
import com.thoughtworks.xstream.converters.collections.CollectionConverter;
import com.thoughtworks.xstream.mapper.Mapper;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import xstreamfxextensions.Person;

/**
 * TODO write documentation<br>
 * <br>
 * Created at 21/09/11 09:32.<br>
 *
 * @author Antoine Mischler <antoine@dooapp.com>
 * @since 2.2
 */
public class ObservableListConverter extends CollectionConverter implements Converter {

    public ObservableListConverter(Mapper mapper) {
        super(mapper);
    }

    @Override
    public boolean canConvert(Class type) {
        return ObservableList.class.isAssignableFrom(type);
    }

    @Override
    protected Object createCollection(Class type) {
        if (type == ObservableListWrapper.class) {
            return FXCollections.<Person>observableArrayList();
        }
        return super.createCollection(type);
    }
}

Explanation: ObservableListWrapper does not have a no argument constructor but has to be created with the FXCollections.observableArrayList() factory method.

So all well and good...

Until you try to to mark the collection with @XStreamImplicit In which case you get the same problem.

Any help with this gratefully appreciated!