Problem with XMLDecoder and a custom ClassLoader

Question

NOTE: Posted over in Serialization forum as more appropriate there, sorry for the crosspost but didn't notice that forum at first. Please direct any replies there.
I am implementing an application based around Java Plugin Framework (jpf.sourceforge.net). In short one consequence of this framework is that each plugin uses its own classloader with scope of that plugins classes.
One plugin I am using requires the ability to deserialize objects from a javabean xml file. I am using XMLDecoder to do this, and I used the constructor to pass the current plugin ClassLoader to it.
This however only partially seems to work, this is a shortened extract from an example xml
<java version="1.5.0" class="java.beans.XMLDecoder">
<object class="usermanager.javabeans.BeanUser">
  <string>drftpd</string>
  <void property="downloadedBytes">
   <long>737132544</long>
  </void>
  <void property="hostMaskCollection">
   <void method="add">
    <object class="usermanager.HostMask">
     <string>*@*</string>
    </object>
   </void>
  </void>
   <void property="keyedMap">
   <void method="put">
    <object class="dynamicdata.Key">
     <class>commands.UserManagement</class>
     <string>slots</string>
     <class>java.lang.Integer</class>
    </object>
    <int>0</int>
   </void>
etc...Now without passing XMLDecoder a ClassLoader as would be expected I get a ClassNotFoundException for the first <object>.
However if I pass XMLDecoder the correct ClassLoader it reads the xml fine until it reaches <class>commands.UserManagement</class> at which point again I get a ClassNotFoundException.
Here is the stacktrace from that exception:
java.lang.ClassNotFoundException: commands.UserManagement
     at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
     at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
     at java.lang.Class.forName0(Native Method)
     at java.lang.Class.forName(Class.java:242)
     at com.sun.beans.ObjectHandler.classForName(ObjectHandler.java:67)
     at com.sun.beans.ObjectHandler.classForName(ObjectHandler.java:54)
     at java.beans.Statement.invoke(Statement.java:140)
     at java.beans.Expression.getValue(Expression.java:98)
     at com.sun.beans.MutableExpression.getValue(ObjectHandler.java:400)
     at com.sun.beans.ObjectHandler.getValue(ObjectHandler.java:106)
     at com.sun.beans.ObjectHandler.endElement(ObjectHandler.java:327)
     at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:625)
     at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1241)
     at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(XMLDocumentFragmentScannerImpl.java:1685)
     at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:368)
     at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:834)
     at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:764)
     at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:148)
     at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1242)
     at javax.xml.parsers.SAXParser.parse(SAXParser.java:344)
     at javax.xml.parsers.SAXParser.parse(SAXParser.java:120)
     at java.beans.XMLDecoder.readObject(XMLDecoder.java:205)
     at usermanager.javabeans.BeanUserManager.loadUser(BeanUserManager.java:128)
Now after looking through some of the source it appears to me at least that XMLDecoder when processing an <object> uses an ObjectHandler with the ClassLoader as a parameter, however a class contained within a <class> element gets handled by Statement.invoke() which uses an ObjectHandler without a ClassLoader specified thus using the standard ClassLoader.
I've managed to work around it for now by setting the contextClassLoader to the correct one before calling readObject() in XMLDecoder and then reverting it back immediately after, but this feels like somewhat of a hack to me.
I would've expected it to have been properly handled when passing the ClassLoader to XMLDecoder rather than like it is.
Anyone know if this is intended behaviour or a bug? and if the former is there any recommended way to deal with this other than the one I'm currently using.
NOTE: Posted over in Serialization forum as more appropriate there, sorry for the crosspost but didn't notice that forum at first. Please direct any replies there.
Message was edited by:
djb61
NOTE: Reposting to Serialization

Answer 1

You can provide a cell renderer to the JTree to paint the checkBox.
The following code checks or unchecks the box with each click also:
_tree.setCellRenderer(new DefaultTreeCellRenderer()
  private JCheckBox checkBox = null;
  public Component getTreeCellRendererComponent(JTree tree,
                                                Object value,
                                                boolean selected,
                                                boolean expanded,
                                                boolean leaf,
                                                int row,
                                                boolean hasFocus)
    // Each node will be drawn as a check box
    if (checkBox == null)
      checkBox  = new JCheckBox();
      checkBox .setBackground(tree.getBackground());
    DefaultMutableTreeNode node = (DefaultMutableTreeNode)value;
    checkBox.setText(node.getUserObject().toString());
    checkBox.setSelected(selected);
    return checkBox;
});