Question

I have a Java\Spring\Hibernate application – complete with domain classes which are basically Hibernate POJOs

There is a piece of functionality that I think can be written well in Grails.

I wish to reuse the domain classes that I have created in the main Java app

What is the best way to do so ?

Should I write new domain classes extending the Java classes ? this sounds tacky
Or Can I ‘generate’ controllers off the Java domain classes ?

What are the best practices around reusing Java domain objects in Grails\Groovy
I am sure there must be others writing some pieces in grails\groovy

If you know about a tutorial which talks about such an integration- that would be awesome !!!

PS: I am quite a newbie in grails-groovy so may be missing the obvious. Thanks !!!

Answer 1

Do you really want/need to use Grails rather than just Groovy?

Grails really isn’t something you can use to add a part to an existing web app. The whole “convention over configuration” approach means that you pretty much have to play by Grails’ rules, otherwise there is no point in using it. And one of those rules is that domain objects are Groovy classes that are heavily “enhanced” by the Grails runtime.

It might be possible to have them extend existing Java classes, but I wouldn’t bet on it – and all the Spring and Hibernate parts of your existing app would have to be discarded, or at least you’d have to spend a lot of effort to make them work in Grails. You’ll be fighting the framework rather than profiting from it.

IMO you have two options:

• Rewrite your app from scratch in Grails while reusing as much of the existing code as possible.
• Keep your app as it is and add new stuff in Groovy, without using Grails.

The latter is probably better in your situation. Grails is meant to create new web apps very quickly, that’s where it shines. Adding stuff to an existing app just isn’t what it was made for.

EDIT:
Concerning the clarification in the comments: if you’re planning to write basically a data entry/maintenance frontend for data used by another app and have the DB as the only communication channel between them, that might actually work quite well with Grails; it can certainly be configured to use an existing DB schema rather than creating its own from the domain classes (though the latter is less work).