Hi Michael,
Michael Mogley wrote:
> Hi Jörg,
>
> Ok, I wrote a small self-contained class to illustrate the issue:
>
> import java.io.EOFException;
> import java.io.ObjectInputStream;
> import java.util.LinkedList;
> import java.util.List;
>
> import org.apache.commons.io.IOUtils;
> import org.apache.commons.lang3.StringUtils;
> import org.slf4j.Logger;
> import org.slf4j.LoggerFactory;
>
> import com.thoughtworks.xstream.XStream;
>
> public class TestXStreamReferencing
> {
> //~ Statics
> ------------------------------------------------------------------
>
> static private final Logger LOG =
> LoggerFactory.getLogger(TestXStreamReferencing.class);
>
> //~ Methods
> ------------------------------------------------------------------
>
> public static void main(String[] args)
> {
> try
> {
> String xml = StringUtils.join(new String[] {
> "<list>",
> " <typeA/>",
> " <typeA/>",
> " <typeB>",
> " <items>",
> " <typeA reference=\"../../../typeA[2]\"/>",
> " </items>",
> " </typeB>",
> "</list>"
> }, "\n");
>
> // Read objects.
> XStream xsUsersAndGroups = new XStream();
> xsUsersAndGroups.alias("typeA", TypeA.class);
> xsUsersAndGroups.alias("typeB", TypeB.class);
>
> ObjectInputStream isUsersAndGroups =
> xsUsersAndGroups.createObjectInputStream(IOUtils.toInputStream(xml));
>
> try
> {
> while (true)
> {
> Object nextObject = isUsersAndGroups.readObject();
>
> LOG.info("read: {}", nextObject);
> }
> }
> catch (EOFException e)
> {
> }
> }
> catch (Throwable t)
> {
> LOG.error(t.getMessage(), t);
> }
> }
[snip]
OK, this explains it. Reading or writing individual objects in an
ObjectStream does not preserve references between those objects. Each
writeObject/readObject call is a separate marshalling process. Have alook at
XStream's acceptance tests. In MultipleObjectsInOneStream is a workaround
with a custom MarshallingStrategy that overcomes this limitation.
Hope this helps,
Jörg
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