[jdom-interest] Serialization Trouble through Inheritance

[Rolf Lear]

Hi Björn 

I don't have my 'JDOM Laptop' with me at the moment, so I can't easily
reproduce your problem, but, I suspect this is just an issue of
implementing your own read/write object methods.

What happens if you add the following methods to your 'MyElement' class? I
believe this should fix things..... try it... :-)



	/**
	 * Serialize out the MyElement.
	 * 
	 * @serialData
	 * The Stream protocol is:
	 * <ol>
	 *   <li>Write the super Element class out...
	 * </ol>
	 * 
	 * @param out where to write the Element to.
	 * @throws IOException if there is a writing problem.
	 */
	private void writeObject(final ObjectOutputStream out) throws IOException
{
		out.defaultWriteObject();
	}

	/**
	 * Read a MyElement off the ObjectInputStream.
	 * 
	 * @see #writeObject(ObjectOutputStream)
	 * @param in where to read the Element from.
	 * @throws IOException if there is a reading problem.
	 * @throws ClassNotFoundException when a class cannot be found
	 */
	private void readObject(final ObjectInputStream in)
			throws IOException, ClassNotFoundException {
		in.defaultReadObject();
	}


Rolf



On Thu, 09 Aug 2012 16:08:48 +0200, Björn Buchner
<b.buchner at isys-software.de> wrote:
> Hi Folks,
> 
> I am using the JDOM 2.0.2 release and experienced some trouble when it 
> comes to serialization.
> 
> De-/serializing an Element object through the standard 
> ObjectOutput/InputStream is no problem. Trouble starts when I try to 
> deserialize an object of a class that inherits from Element.
> 
> It always ends with a InvalidClassException: no valid constructor. 
> Normally this indicates that JRE is missing a public default 
> constructor, but as you can see in the example below the subclass
> has a default constructor.
> 
> Thanks in advance for your help
> 
> Example code:
> 
> public class MyElement extends Element {
> 
>      private static final long serialVersionUID = -4220756491425652053L;
> 
>      public MyElement() {
>          super();
>      }
> 
> 
>      public static void main(String ... args) throws IOException, 
> ClassNotFoundException {
>         ByteArrayOutputStream buffer = new ByteArrayOutputStream();
>         ObjectOutputStream outStream = new ObjectOutputStream(buffer);
> 
>         MyElement element = new MyElement();
> 
>         outStream.writeObject(element);
>         outStream.flush();
>         ObjectInputStream inStream = new ObjectInputStream(new 
> ByteArrayInputStream(buffer.toByteArray()));
>         element = (MyElement)inStream.readObject();
>      }
> }
> 
> Result:
> 
> Exception in thread "main" java.io.InvalidClassException: 
> <packageremoved>; no valid constructor
>      at 
>
java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(ObjectStreamClass.java:147)
>      at 
> java.io.ObjectStreamClass.checkDeserialize(ObjectStreamClass.java:755)
>      at 
>
java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1751)
>      at
java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1347)
>      at java.io.ObjectInputStream.readObject(ObjectInputStream.java:369)
>      at <packageremoved>.main(MyElement.java:29)