UserType with non-public constructor?

lmiranda · **Joined:** Mon Nov 29, 2004 2:26 pm **Posts:** 28

Hi,

I would like to persist a typesafe enumeration in Hibernate without breaking the pattern, so I'd like to keep my constructors private if possible.

I was under the belief that Hibernate would support constructing objects with private and protected constructors via the Reflection API (when given sufficient security permissions of course) as it does for properties.

However, the constructor for CustomType uses Class.newInstance() to instantiate my persistent enum, which yields an IllegalAccessException (context shown in code snippet below).

Is there a reason why CustomType does not use ReflectHelper.getDefaultConstructor(Class clazz) to "safely" get a reference to the class's default constructor and then instantiate it? Doing this would cause AccessibleObject.setAccessible(true) to be called on my enumeration's private default constructor, which is exactly what I would like to happen

Code:

public class CustomType extends AbstractType {
   
   // ...
   
   public CustomType(Class userTypeClass) throws MappingException {
      
      name = userTypeClass.getName();

      try {
         userType = (UserType) userTypeClass.newInstance();
      }
      catch (InstantiationException ie) {
         throw new MappingException( "Cannot instantiate custom type: " + userTypeClass.getName() );
      }
      catch (IllegalAccessException iae) {

         // ******************
         // I get this error:
         // ******************
         throw new MappingException( "IllegalAccessException trying to instantiate custom type: " + userTypeClass.getName() );

      }
      catch (ClassCastException cce) {
         throw new MappingException( userTypeClass.getName() + " must implement net.sf.hibernate.UserType" );
      }
      types = userType.sqlTypes();

      if ( !Serializable.class.isAssignableFrom( userType.returnedClass() ) ) {
         LogFactory.getLog(CustomType.class).warn("custom type does not implement Serializable: " + userTypeClass);
      }
   }

   /...
}

Many thanks,
Luís

PS I'm referring to Hibernate 2.1.6

max · **Posted:** Mon Nov 29, 2004 3:16 pm

what custom type do you have that need to not have a public constructor ?

custom types normally doesn't contain a single line of businesscode - only some glue code between your domain to hibernate.....so hard to find a usecase for it - please show me ?

and besides if you think you have a fix then please provide a patch instead of some halfbaked code ;)

lmiranda · **Joined:** Mon Nov 29, 2004 2:26 pm **Posts:** 28

I'd be happy to provide a fix, I'm just not sure if it's something that needs to be fixed or if it should behave this way by design.

I'm not using CustomType directly but this is where the exception crops up. I'm implementing UserType so I can persist a typesafe enumeration, as described in this link: UserType for persisting a Typesafe Enumeration with a VARCHAR column.

So I have a persistent Enum base class:

Code:

public abstract class Enum implements Serializable, Comparable, UserType {
    // default constructor for hibernate
    protected Enum() {
        super();
    }

    // implement the interfaces...
}

And a concrete typesafe enumeration:

Code:

public final class ProvisioningState extends Enum {
    // default constructor for hibernate
    private ProvisioningState() {
        super();
    }

    private ProvisioningState(int ordinal, String name) {
        super(ordinal, name);
    }

    public static final ProvisioningState FOO = new ProvisioningState(0, "Foo");
    public static final ProvisioningState BAR = new ProvisioningState(1, "Bar");
}

I would like the constructors to remain non-public to prevent a user of this class from instantiating it.

The (interesting part of the) stack trace I get:

curio · **Joined:** Tue Oct 05, 2004 9:45 am **Posts:** 263

hi,

just a remark (perhaps i'm mixing something) ...

The UserType should not be your "Enum" or "ProvisioningState" ..
the UserType can 'only' handle it ...!

gtx
curio

max · **Posted:** Tue Nov 30, 2004 6:59 am

you are not following the example ;)

The business type (in your case Enum and Rating - btw. Enum is a reaally bad name to use as enum is a keyword in 1.5) should not implement/extends UserType.

You should have an additional EnumUserType class, so you remove the hibernate dependency from your code - and thus also don't have much need to not having a default constructor on the UserType.

lmiranda · **Joined:** Mon Nov 29, 2004 2:26 pm **Posts:** 28

max wrote:

btw. Enum is a reaally bad name to use as enum is a keyword in 1.5

Oops. Duly noted, thanks. :)

max wrote:

You should have an additional EnumUserType class, so you remove the hibernate dependency from your code - and thus also don't have much need to not having a default constructor on the UserType.

Sorry, the example that was followed was actually UserType for persisting Typesafe Enumerations with a single class. Even with the first example, however, I would argue that the constructor should be private in order to prevent instantiation of this class by a user.

max · **Posted:** Tue Nov 30, 2004 7:27 am

well - it cannot come out of sync nor be used to much ;)

...but again, you are welcoem to provide a patch if you would like to have the opportunity to have it use the reflection trick.

max · **Posted:** Tue Nov 30, 2004 7:29 am

and regarding that page - it is a bad example ;(

i'll make a comment on that page about it.

lmiranda · **Joined:** Mon Nov 29, 2004 2:26 pm **Posts:** 28

You're right, this solution creates an unwanted dependency on Hibernate instead of the "transparent persistency" that we would like. I will probably end up using the 2-class solution as it is conceptually nicer (although more work). ;)

For those who don't care about this dependency, however, I think ability to keep the constructor private would be useful, so I'll be submitting a patch.

Thanks again,
Luís