Best Practice for Spring MVC form-backing object tree initialization?

Call it overkill if you like, but what we actually ended up doing was to create a generic factory that will take any object and use reflection to (recursively) find all the null properties and instantiate an object of the correct type. I did this using Apache Commons BeanUtils This way you can take an object that you may have gotten from various sources (a DAO, deserialization from XML, whatever), pass it through this factory, and use it as a form-backing object without worrying that something you need for binding may be null Admittedly, this means instantiating properties that we may not need for a given form, but in our case that doesn't typically apply.

Call it overkill if you like, but what we actually ended up doing was to create a generic factory that will take any object and use reflection to (recursively) find all the null properties and instantiate an object of the correct type. I did this using Apache Commons BeanUtils. This way you can take an object that you may have gotten from various sources (a DAO, deserialization from XML, whatever), pass it through this factory, and use it as a form-backing object without worrying that something you need for binding may be null.

Admittedly, this means instantiating properties that we may not need for a given form, but in our case that doesn't typically apply.

Just for curiosity: To get your goal, do you use BeanUtils. CloneBean method? If not, would it be possible you show how to?

– Arthur Ronald F D Garcia May 18 '10 at 18:13 No, I don't use cloneBean. Briefly, the situation might be, for example, that I could have a Contact object that has an Address property which is null. I need to put a new Address object there.So I use PropertyDescriptor.getPropertyType() to get the property's class, and then use Class.getConstructor().newInstance() to instantiate it.

The only complexity is that in some cases the property type is an interface; in those cases, for the application I described, I rely on the naming convention that we used for interfaces -- if the interface is IAddress, the implementation is Address. – JacobM May 18 '10 at 18:21.

Not clear for me but assuming i'm right :) : 1) Yes, When you write person.contactInfo.homeAddress. Street , read person.getContactInfo().getHomeAddress().getStreet(). If ContactInfo or HomeAddress or Street objects are null, invocation of one of their method raises a NullPointException.

2)I usually initializes member objects at declaration, just like in code snippet. Don't see the benefit of factory class to do the job if initialization values are inconditionnal. I don't clearly see the problem where you are forced to create a Person twice... but I may be tired ;).

If I'm retrieving stuff from the database, then the initialization at declaration will create a ContactInfo, which will then be replaced by another ContactInfo created by the DAO with data in it. So I'll have created an extra one. – JacobM Dec 19 '08 at 14:23.

I would generally make sure objects are fully initialized - it makes using the object that much simplier and avoids you scattering null checks throughout your code. In the case you give here I'd probably put the initialization in the getter so the child object is only instantiated when it's actually going to be used, ie: when the getter is called and then only if it's null. In terms of loading from the database with one-to-one relationships I'd normally do the join and load the lot.

The performance impact is typically minimal but you should be aware that there may be one. When it comes to one-to-many relationships I normally go for lazy loading. Bernate will take of this for you, but if you're rolling your own then you just need a custom implementation of List that calls the appropriate DAO when any of the methods relating to its contents are called.

The one exception to this behavior with one-to-many relationships is when you've got a list of parent objects that you intend to iterate over and for each parent you want to iterate over its children. Obviously the performance would suck because you'd be making a n + 1 calls to the DB when you could actually do it with 2 calls.

Thanks. I like the idea of putting the initialization in the getter; best of both worlds for me. I'll try it out and mark this as the "answer" if it seems to be working out.

For collections I like to use LazyList from Apache Commons. It allows you to specify a factory. – JacobM Dec 19 '08 at 14:24 1 Addendum to the LazyList point -- it turns out that Spring has a lazy list itself called AutoPopulatingList.

– JacobM Jan 23 '09 at 17:20.

I've gone with the Factory method approach (not a fan of using a seperate class for it, to me it makes more sense to have it in a static method so it's all in one place). I have something like - public static Person getInstanceForContactInfoForm() { ContactInfo contactInfo = ContactInfo. GetInstanceForContactInfoForm(); Person person = new Person(contactInfo); // set whatever other properties you need for Person // just enough to 1-render the form and 2-avoid any exceptions return person; } If I'm loading the Person from the database, I have a method in the Person class called something like "initalizeForContactInfoForm" or something.

After loading the Person from the database, I'll call this method in the Service layer in the method that is called by the Spring MVC method which returns the Form Backing Object. I don't think this is a really a convention, it's just an approach I cooked up on my own. I don't really see what any drawbacks are so if somebody disagrees please let me know...

Drawback for us is that we're frequently using a given instance as the form backing object for multiple forms. Also, of course, this increases the overhead of adding a new form or adding new fields to a form -- now you have to change the object and the DAO in addition to the form. – JacobM Jan 23 '09 at 17:28.

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