Hibernate jars in client tier

rcasturi · **Joined:** Thu Nov 06, 2003 10:04 pm **Posts:** 22

I have come across an issue where I am finding myself the need to include hibernate jars (specifically hibernate2.jar and odmg.jar) in the client tier jars. The reason is this.

Since I have a rather complex object hierarchy in my J2EE environment, I am using my business classes themselves as the ones that are mapped for Hibernate to persist. And they are also being sent across to remote clients for viewing in a GUI.

Now in some of the business classes, there are collections which have been specified as java.util.List. Hibernate I understand sometimes replaces those List collections with net.sf.hibernate.List implementations. So when those business classse with those List collections get to the client side, I am getting ClassNotFoundException if I donot have the hibernate jars on the client classpath.

I wanted to know if anyone has any ideas to cleanly resolve this, or if I am stuck with having to include those jars to send to the client. Ofcourse the better solution is to convert the complex business objects to more simpler data transfer objects and send those to the client. But I wanted to find out if what I described is a common scenario and if there are any solutions.

Thanks
Rama

VampBoy · **Posted:** Wed Feb 25, 2004 6:14 pm

Well, you are not alone. We too have encountered the same scenario and are simply putting the required .jar files on the client.

Your suggestion of 'replacing' the hibernate implementation of list with say, for example, an ArrayList is all fine on the surface. However, bear in mind that the hibernate implementations for collections keep track of state for the sake of performing cascading operations. Simply replacing those lists would break that horribly I would think.

RobJellinghaus · **Joined:** Thu Jan 08, 2004 6:17 pm **Posts:** 278

No, the Hibernate collections are safe to serialize to the client side. Since the client side has no session anyway, the collections' lazy loading state does not need to be preserved.

I think the only real answer to the problem of exposing the client to business classes or persistence classes that they shouldn't really see is to do some kind of DTO mapping to plain data classes without Hibernate or business-logic code.

This post (in a long thread about all these issues) outlines one hbm2java extension to make it at least easier to create the basic POJOs themselves, and then writing the generic DTO converter is at least possible without needing any further code generation. (Still hope to put my money where my mouth is on that....)

Cheers,
Rob

RobJellinghaus · **Joined:** Thu Jan 08, 2004 6:17 pm **Posts:** 278

...And since the collections' lazy loading state does not need to be preserved, it is safe to change the collections altogether from Hibernate collections to java.util collections.

(Though see this thread discussing the problems when you save a (cascaded) object graph that uses getID() for equals() and hashCode(), and that has been (partially) stored in hashed collections before being saved....)

Cheers!
Rob

rcasturi · **Joined:** Thu Nov 06, 2003 10:04 pm **Posts:** 22

So are you saying other than using some kind of DTO mapping to our business objects, no one has found a better solution. I really donot like the idea of having to maintain two almost identical class hierarchies, one for the business/domain classes and one for their DTO equivalents. And especially I donot like the idea of having to replace hibernate specific collection implementations in the DTO instances everytime I do persistence related work.

If the answer is that we have to include hibernate jars, is there a minimal jar in hibernate bundle that can be sent to the client that just includes the basic types of hibernate. Is this a feasible idea?

christian · **Posted:** Thu Feb 26, 2004 2:19 pm

There is no minimal JAR. You only need the hibernate2.jar and cglib2.jar (about 1 MB) on the client to successfully deserialize a detached object graph. It's not perfect, but it might be OK for a Webstart/static installation in a LAN.

baliukas · **Posted:** Thu Feb 26, 2004 3:09 pm

I am not sure it will work, but
It must be possible to serialize collections as standard implementations and proxies as original objects traspariently (replace in "writeReplace" method). Doe's somebody tried it ?

rcasturi · **Joined:** Thu Nov 06, 2003 10:04 pm **Posts:** 22

Can you please explain what you mean by "replace in "writeReplace" method"? I am not sure I understood your point.

baliukas · **Posted:** Thu Feb 26, 2004 4:20 pm

"writeReplace" method is specified in java serialization. I am not sure it is a good idea, but it is possible to serialize collection this way:

"Serializable classes that need to designate an alternative object to be used when writing an object to the stream should implement this special method with the exact signature:

ANY-ACCESS-MODIFIER Object writeReplace() throws ObjectStreamException;
"

class MyCollection extends AbstractCollection implements Serializable{

Object writeReplace(){

return new ArrayList(this);

}

}

Serialization will put ArrayList to stream not instance of MyCollection and
ArrayList will be deserialized on client side. It is possible to test

emmanuel · **Posted:** Mon Mar 01, 2004 11:41 am

Note that all-delete-orphanj won't work this way. collection state is keep in Hibernate collection implementation

rcasturi · **Joined:** Thu Nov 06, 2003 10:04 pm **Posts:** 22

So the solution to this is either use DTO mechanism or send hibernate jars to the client? Is that correct?

RobJellinghaus · **Joined:** Thu Jan 08, 2004 6:17 pm **Posts:** 278

Yes, that's correct.

aamir · **Joined:** Sun Oct 03, 2004 9:00 am **Posts:** 7

I was experiencing the same problem and it solved when i copied odmg-3.0.jar, hibernate2.jar and cgi-full.lib.jar.

However, I am facing the Mismatched Serialization UIDs problem in my Eclipse RCP. All Java VM arguments are same in stande alone and Eclipse RCP. Following is the stack trace of this exception:

java.rmi.MarshalException: CORBA MARSHAL 1229125786 No; nested exception is:
org.omg.CORBA.MARSHAL: Unable to read value from underlying bridge : Mismatched serialization UIDs : Source (Rep. IDRMI:java.util.HashMap:86573568A211C011:0507DAC1C31660D1) = 0507DAC1C31660D1 whereas Target (Rep. ID RMI:dash.hms.common.bo.ServiceCategory:ED162ABB6FFDC0FF:45A41691EA4BC44E) = 45A41691EA4BC44E vmcid: 0x4942f000 minor code: 2202 completed: No
at com.sun.corba.se.impl.javax.rmi.CORBA.Util.mapSystemException(Util.java:197)
at javax.rmi.CORBA.Util.mapSystemException(Util.java:67)
at dash.hms.client._SetupService_Stub.getServiceCategory(_SetupService_Stub.java:772)
at dash.hms.ui.HMSPlugin.start(HMSPlugin.java:70)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl$1.run(BundleContextImpl.java:958)
at java.security.AccessController.doPrivileged(Native Method)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleContextImpl.java:954)
at org.eclipse.osgi.framework.internal.core.BundleContextImpl.start(BundleContextImpl.java:937)
at org.eclipse.osgi.framework.internal.core.BundleHost.startWorker(BundleHost.java:417)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.start(AbstractBundle.java:293)
at org.eclipse.core.runtime.adaptor.EclipseClassLoader.findLocalClass(EclipseClassLoader.java:110)
at org.eclipse.osgi.framework.internal.core.BundleLoader.findLocalClass(BundleLoader.java:371)
at org.eclipse.osgi.framework.internal.core.BundleLoader.findClass(BundleLoader.java:402)
at org.eclipse.osgi.framework.adaptor.core.AbstractClassLoader.loadClass(AbstractClassLoader.java:93)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at org.eclipse.osgi.framework.internal.core.BundleLoader.loadClass(BundleLoader.java:307)
at org.eclipse.osgi.framework.internal.core.BundleHost.loadClass(BundleHost.java:332)
at org.eclipse.osgi.framework.internal.core.AbstractBundle.loadClass(AbstractBundle.java:1315)
at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:161)
at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:151)
at org.eclipse.core.internal.registry.ConfigurationElement.createExecutableExtension(ConfigurationElement.java:138)
at org.eclipse.core.internal.registry.ConfigurationElementHandle.createExecutableExtension(ConfigurationElementHandle.java:48)
at org.eclipse.core.internal.runtime.PlatformActivator$1.run(PlatformActivator.java:216)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:273)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:129)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.eclipse.core.launcher.Main.basicRun(Main.java:185)
at org.eclipse.core.launcher.Main.run(Main.java:710)
at org.eclipse.core.launcher.Main.main(Main.java:694)
Caused by: org.omg.CORBA.MARSHAL: Unable to read value from underlying bridge : Mismatched serialization UIDs : Source (Rep. IDRMI:java.util.HashMap:86573568A211C011:0507DAC1C31660D1) = 0507DAC1C31660D1 whereas Target (Rep. ID RMI:dash.hms.common.bo.ServiceCategory:ED162ABB6FFDC0FF:45A41691EA4BC44E) = 45A41691EA4BC44E vmcid: 0x4942f000 minor code: 2202 completed: No
at com.ibm.rmi.iiop.CDRInputStream.read_value(CDRInputStream.java:1745)
at dash.hms.client._SetupService_Stub.getServiceCategory(_SetupService_Stub.java:761)
... 29 more