How to store java objects in the DB?

I'm an undergraduate student in computer science, Brazil. I`m having a problem 
regarding the java objects storage in the DB. Here is deal:

                      ---------------
                      |  interface  |
                      |  MY_INTERF  |
                      |             |
                      |  invoke()   |
                      ---------------
                            |
              --------------------------------------------------------------
              |                               |                        |
       ---------------                  ---------------
       |   object    |                  |   object    |
       |  MY_OBJ A   |                  |  MY_OBJ B   |
       |             |                  |             |           * * * * * 
       |  invoke()   |                  |  invoke()   |
       ---------------                  ---------------

I need to store the "MY_OBJ A", "MY_OBJ B", ..  objects that implements 
the "MY_INTERF" interface in a conteiner (such as a Vector or a Hashtable one) 
of a Factory Object (like the Garage one). The objects "MY_OBJ A", "MY_OBJ B" 
are serializable, but the following error happens when processing with OPP:

PvOGenericInstanceImpl:
java.lang.ClassNotFoundException: PvOGenericInstanceImpl
	at java.net.URLClassLoader$1.run(URLClassLoader.java:198)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:186)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:299)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:265)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:255)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:315)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:140)
	at org.ozoneDB.tools.OPP.OPP.makeProxy(OPP.java:224)
	at org.ozoneDB.tools.OPP.OPP.makeProxies(OPP.java:199)
	at org.ozoneDB.tools.OPP.OPP.main(OPP.java:147)

Some one can help me?



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