[Hibernate-issues] [Hibernate-JIRA] Created: (HB-320) Allow java.beans.XMLEncoder to process persisted classes possessing collections

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  A new issue has been created in JIRA.

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  http://opensource.atlassian.com/projects/hibernate/secure/ViewIssue.jspa?=
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Here is an overview of the issue:
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        Key: HB-320
    Summary: Allow java.beans.XMLEncoder to process persisted classes posse=
ssing collections
       Type: Improvement

     Status: Unassigned
   Priority: Minor

    Project: Hibernate2
 Components:=20
             core
   Versions:
             2.1 beta 3

   Assignee:=20
   Reporter: Roberto S. Tyley

    Created: Tue, 9 Sep 2003 7:27 AM
    Updated: Tue, 9 Sep 2003 7:27 AM
Environment: Win 2000, JDK 1.4.2

Description:

java.beans.XMLEncoder was introduced in J2SE v1.4, and provides a convenien=
t method of serialising an object graph to an XML file:

http://java.sun.com/j2se/1.4.2/docs/api/java/beans/XMLEncoder.html

It would be nice to be able to extract a copy of the information stored in =
a hibernate database as an XML file, ie. by doing a hibernate query to get =
the information you want (possibly "from o in class java.lang.Object", or w=
hatever), and translate this object graph to XML using XMLEncoder. Unfortun=
ately, this approach does not work in the common case of persisted classes =
possessing collections - a LazyInitializationException is raised processing=
 the collection (an example trace is included below). This exception occurs=
 even if your session is still open, in fact even if you disable lazy initi=
alization, because of the approach used by XMLEncoder to check for circular=
ities in the object graph. When asked to persist an object, XMLEncoder appe=
ars to instantiate a new instance of that class, to allow it to check if it=
 already has a suitable previous reference to the object (see java.beans.Pe=
rsistenceDelegate.writeObject()). Unfortunately, when a net.sf.hibernate.co=
llection.PersistentCollection has this treatment, the instantiatation of th=
e new instance does not appear supply it with a reference to the Session ob=
ject- XMLEncoder's further attempts to query the state of the collection fa=
il with a LazyInitializationException. If your object graph has yet to be p=
ersisted, ie. the collections in it are still vanilla HashMaps, etc, the XM=
LEncoder will work fine.

XMLEncoder is intended to be a JavaBean serialiser, and as Hibernate persis=
ted classes have to conform to the JavaBean pattern, you'd expect the XMLEn=
coder to work well here - is there a possibility of allowing this to happen=
? I think one possible line of attack may be providing a series of java.bea=
ns.PersistenceDelegate classes to handle hibernate collections - any other =
ideas?!

cheers,
Roberto

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Trace follows below:

net.sf.hibernate.LazyInitializationException: Failed to lazily initialize a=
 collection - no Session
=09at net.sf.hibernate.collection.PersistentCollection.initialize(Persisten=
tCollection.java:164)
=09at net.sf.hibernate.collection.PersistentCollection.read(PersistentColle=
ction.java:63)
=09at net.sf.hibernate.collection.Set.size(Set.java:108)
=09at java.util.AbstractSet.equals(AbstractSet.java:72)
=09at java.beans.DefaultPersistenceDelegate.equals(DefaultPersistenceDelega=
te.java:207)
=09at java.beans.DefaultPersistenceDelegate.doProperty(DefaultPersistenceDe=
legate.java:220)
=09at java.beans.DefaultPersistenceDelegate.initBean(DefaultPersistenceDele=
gate.java:254)
=09at java.beans.DefaultPersistenceDelegate.initialize(DefaultPersistenceDe=
legate.java:395)
=09at java.beans.PersistenceDelegate.writeObject(PersistenceDelegate.java:1=
03)
=09at java.beans.Encoder.writeObject(Encoder.java:55)
=09at java.beans.XMLEncoder.writeObject(XMLEncoder.java:250)
=09at java.beans.Encoder.writeExpression(Encoder.java:260)
=09at java.beans.XMLEncoder.writeExpression(XMLEncoder.java:363)
=09at java.beans.PersistenceDelegate.writeObject(PersistenceDelegate.java:1=
00)
=09at java.beans.Encoder.writeObject(Encoder.java:55)
=09at java.beans.XMLEncoder.writeObject(XMLEncoder.java:250)
=09at java.beans.Encoder.writeObject1(Encoder.java:192)
=09at java.beans.Encoder.cloneStatement(Encoder.java:205)
=09at java.beans.Encoder.writeStatement(Encoder.java:236)
=09at java.beans.XMLEncoder.writeStatement(XMLEncoder.java:326)
=09at java.beans.DefaultPersistenceDelegate.invokeStatement(DefaultPersiste=
nceDelegate.java:242)
=09at java.beans.java_util_List_PersistenceDelegate.initialize(MetaData.jav=
a:245)
=09at java.beans.PersistenceDelegate.initialize(PersistenceDelegate.java:19=
1)
=09at java.beans.DefaultPersistenceDelegate.initialize(DefaultPersistenceDe=
legate.java:393)
=09at java.beans.PersistenceDelegate.writeObject(PersistenceDelegate.java:1=
03)
=09at java.beans.Encoder.writeObject(Encoder.java:55)
=09at java.beans.XMLEncoder.writeObject(XMLEncoder.java:250)
=09at java.beans.Encoder.writeExpression(Encoder.java:260)
=09at java.beans.XMLEncoder.writeExpression(XMLEncoder.java:363)
=09at java.beans.PersistenceDelegate.writeObject(PersistenceDelegate.java:1=
00)
=09at java.beans.Encoder.writeObject(Encoder.java:55)
=09at java.beans.XMLEncoder.writeObject(XMLEncoder.java:250)
=09at java.beans.Encoder.writeObject1(Encoder.java:192)
=09at java.beans.Encoder.cloneStatement(Encoder.java:205)
=09at java.beans.Encoder.writeStatement(Encoder.java:236)
=09at java.beans.XMLEncoder.writeStatement(XMLEncoder.java:326)
=09at java.beans.XMLEncoder.writeObject(XMLEncoder.java:253)
=09at com.thisbedisonfire.madgag.Main.main(Main.java:88)


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