How to persistent static object

Question

JDO always assigns a StateManager to a PersistenceCapable object when
creating instance. If an object is static, it'll keep its StateManager for
ever after instantiation. So If I excute the following code repeadly, kodo
will complain that persistence manager has been closed.
1) Get PersistenceManager
2) Begin transaction
3) Get object from datastore. If not exist, create a new object. This
object is a static.
4) Commit transaction
5) pm.close
For the first time, kodo will assign a new StateManager to this static
object. But for the second time, exception, "persistence manager has been
closed", will arise when excuting some of object's methods. Because each
StateManager object owns a PersistenceManager object. If this pm is
closed, according StateManager object is also useless.
After enhancing, kodo will change some getter/setter methods to
according jdo getter/setter ones. These methods may invoke
startManager.isLoaded(), which invokes pm.isActive(). Unfortunately, pm
has been closed.
Any other tricky methods to persistent static object ?
Thanks !

Answer 1

Dear Marc,
Thanks for your kind help. It's an effective advice to prevent
persistent object from being static.
However, what if the object to be persistent is an enumeration type
constant ? For example :
public class MyEnumType
private String name = null;
private int value = 0;
protected MyEnumType( String name, int value )
this.name = name;
this.value = value;
public static final TYPE_1 = new MyEnumType( "type 1", 1 );
public class EnumTypeUseClass
private MyEnumType type = null;
public void setType(..) {..}
public MyEnumType getType() {..}
public class TestClass
public void f()
PersistenceManager pm = null;
try
// Obtain pm
pm = ...;
pm.currentTransaction().begin();
EnumTypeUseClass use = new EnumTypeUseClass();
// Obtain myenumtype object from datastore
MyEnumType type = getJdoObject( pm, MyEnumType.class, "value ==" +
MyEnumType.TYPE_1.getValue() );
// Following line will cause "PersistenceManager has been closed"
exception
use.setType( type );
pm.makePersistent( use );
pm.currentTransaction().commit();
catch( .. )
finally
pm.close();
public static void main( String args[] )
for( int i = 0; i < 10; i ++ )
f();
Actually, exception is caused by MyEnumType.TYPE_1.getValue() because
this object's pm has been closed in the first loop time.
Now I solved this problem by not persistent MyEnumType objects, and
change type field in EnumTypeUseClass from MyEnumType to int.
But I still wonder how to persistent static objects.
Maybe your first advice is feasible, but I think it will make your
program tangly. Do you think so ? :)
Marc Prud'hommeaux wrote:
Liang-
You are correct that a persistent instance must be associated with a
PersistenceManager. You could always just leave the PersistenceManager
open (if using optimistic transaction, Kodo won't tie up database
resources in this case). Another option is to not have the singleston
instance be a static variable, but have it be obtained via a factory
method that takes a PersistenceManager argument.
If this doesn't help, perhaps you could help clarify the situation by
posting some code that shows that you would like to do?
In article <[email protected]>, Liang Zhilong wrote:
JDO always assigns a StateManager to a PersistenceCapable object when
creating instance. If an object is static, it'll keep its StateManager for
ever after instantiation. So If I excute the following code repeadly, kodo
will complain that persistence manager has been closed.
1) Get PersistenceManager
2) Begin transaction
3) Get object from datastore. If not exist, create a new object. This
object is a static.
4) Commit transaction
5) pm.close
For the first time, kodo will assign a new StateManager to this static
object. But for the second time, exception, "persistence manager has been
closed", will arise when excuting some of object's methods. Because each
StateManager object owns a PersistenceManager object. If this pm is
closed, according StateManager object is also useless.
After enhancing, kodo will change some getter/setter methods to
according jdo getter/setter ones. These methods may invoke
startManager.isLoaded(), which invokes pm.isActive(). Unfortunately, pm
has been closed.
Any other tricky methods to persistent static object ?
Thanks !
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com