InfoQ Article: Grails + EJB Domain Models Step-by-Step

A legacy approach to using EJBs. Wow that speaks volumes.

And do it with another language. Ouch.

Floyd I cant figure if you think Java has a future or if you think we should all party on the VM like it was (a) 1999 (Corba container).

This is what frustrates me about the Java space right now. Everyone is so rattled by ruby and scripts and trying to wedge Java in a buzz trend that is so far removed from where Java is that its not even worth discussing Java in a "rails" context.

Or discussing rails in an EJB context.

If we have to port rails to the JVM to be happy then maybe we should just use the ruby interpreter and support its toolset and let IBM handle the legacy integration as they are so keen to do.

Its not interesting or all that relevant.

I think you missed the point - the article doesn't treat EJB as legacy, it's about developing a domain model in EJB and using Grails to quickly build a web app around it.

Considering strategies like Domain Driven Design, focusing on your domain model in Java and generating the UI around that is an emerging best practice that tools like Grails can enable.

Where was it mentioned that EJB3 is legacy? Grails is all about embracing Java, the platform, language and tools.

Java has a huge future and it speaks volumes for the strength of the platform that Grails and its underlying frameworks (Spring, Hibernate, SiteMesh, Quartz etc.) exist.

In terms of porting Rails, well yes that is one option, but Rails (as with Ruby's runtime) has a very different object model and idioms for developing web applications. One that its contradictory to existing knowledge about specifications like Servlets, JSP and, indeed, EJB.

Grails is not a port of Rails and in fact is very different in many ways including how it is based on Java frameworks.

"built on the Groovy language" and "fully integrated with Java"
"built on the PL/SQL language" and "fully integrated with Java"
"built on Javascript language" and "fully integrated with Java"
"built on ActiveX" and "fully integrated with Java"
"Built on Flash" and "fully integrated with Java"

I didnt miss the point. The point was accessing EJBs with something other than Java. And if EJB 3 is a big plus in combination with another language then *something* in this picture just went legacy.

And something just went "integration strategy"

Thats how you know what legacy is and isnt.

If we were talking about using Grails to build a front-end to a VSAM file, I'd agree with you that we're talking about legacy integration; however, that's not the case.

There's a distinct difference between...

* Using a current technology to integrate with a pre-existing (legacy) application,

versus...

* Using a current technology (like Grails) in concert with another complimentary and current technology (like EJB) to build a new application.

The point was accessing EJBs with something other than Java. And if EJB 3 is a big plus in combination with another language then *something* in this picture just went legacy.

OK Ill give you that, but you cant ignore the undercurrent of the Java space right now which is desperately trying to wedge the competition into its model out of fear of outright rejection.

What if the smalltalk guys had insisted that Java run in a smalltalk VM? What would people have thought of them? The smalltalk VM was way ahead of Java in the early days.

So now the Java scene wants to steal ruby and rails from the cradle and I say well if Java is so great then let Java solve its own problems without coopting the vibe of the scripting languages.

I think Java is trying to change before anyone acknowledges or speaks aloud of a greater failure of OO or more specifically Java projects to deliver.

I think Java is trying to change before
anyone acknowledges or speaks aloud of a greater failure of OO or more
specifically Java projects to deliver.

Any reason why the relationaship management code can't be generated too? It was a little anticlimactic to learn that the developer had to manually edit the generated groovy code just to handle the object relationaships. I'm assuming all that info is stored as annotations in the EJBs.

Hi,
I followed up this step-by-step and successfully run 'grails run-app'.
Everything looked great except this case:
I assigned 3 computers to an employee, for example, jane and I got
3 instances of the same 'jane' listed in the browser(IE6.0) when I click on
employeeBean list link. That seems a bug. How can I fix it?
Thanks.

This is one the todo list: jira.codehaus.org/browse/GRAILS-172

Good catch. Thanks for your feedback.

There's apparently problem with the dynamic list method, which is used to fetch the list of employees. You can track the problem here: jira.codehaus.org/browse/GRAILS-284

This is a really great article and does a very nice job of showing off the features of Grails. However, I was sort of hoping for an article about integrating Grails and EJB. As it is, the author just illustrates the flexibility of the new EJB pojo implementation as well as the rapid development capabilities of Grails. What I'd like to see (and I believe is slated for a release later this year) is the ability to map those beans to/from ones already deployed on an existing EJB container instead of simply using Hibernate and copying the pojo implementations into the project. Maybe this is already possible using some tricks with the Spring configuration, but I don't know Spring well enough to say. In any case, thanks for a great article!

Randall,

Your comment is exactly what I was thinking! I read the article and there's no mention of an app server or anything like that! Just copying the entity code and using that. While Grails looks cool, we've got a lot invested in the JEE resources. Guess we'll have to see what develops!

Yes, thats what I try to find out as well.

Would it be possible to the content of this article in pdf format, to be able to read it offline and print it nicely? Thanks.

Hi,

I am stuck following your steps in a very early stage ("run-app" directly after "create-app"):
(I am running the grails / groovy-versions mentioned above with JDK 1.6.0_03 on Windows XP SP2)

> grails run-app

Welcome to Grails 1.0-RC2 - grails.org/
Licensed under Apache Standard License 2.0
Grails home is set to: C:\Programme\Dev\grails-1.0-RC2

Base Directory: c:\Arbeit\Allgemein\Dev\Projekte\GrailsTest1
Environment set to development
Note: No plugin scripts found
Running script C:\Programme\Dev\grails-1.0-RC2\scripts\RunApp.groovy
groovy.lang.MissingPropertyException: No such property: war for class: java.lang.String
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:48)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.getProperty(ScriptBytecodeAdapter.java:474)
at Config.run(Config.groovy:62)
....

Do you have any hints for me?

Kind regards
Michael

Hello again,

FYI: just fixed the error by changing the line
grails="error"
to
grails.app="error"
in the generated file "grails-app/conf/Config.groovy".

Kind regards
Michael

When I try out the tutorial I get an error which is logged in the JIRA (GRAILS-2042). However there seems to be no action on this issue ? Any workaround available for this ? (am using Grails 1.0 RC3)
- Venky

Jason,

Thanks for the article - it's awesome.
I was wondering what needs to be done to make the following search scrollable...being very new to grails, i'm having a real hard time figuring it out...

I went through Step 1 to 3 with following changes
in ejb3_grails dir
./src/java/com/jasonrudolph/ejb3example/entity/EmployeeBean.java
./src/java/com/jasonrudolph/ejb3example/entity/ComputerBean.java
./grails-app/conf/hibernate/hibernate.cfg.xml
./lib/mysql-connector-java-5.1.6-bin.jar
./grails-app/conf/ApplicationDataSource.groovy
I am not sure about hibernate.cfg.xml location.

At Step 4 - Generate the Scaffolding, I got an error.
% grails generate-controller
.....
No domain class found for name com.jasonroudolph.ejb3example.entity.EmployeeBean.
Please try again and enter a valid domain class name

How to move forward?
Thanks for the help!

The thing I actually need is using the existing EJB 3 domain entities within a GORM entity. For example I already have a User entity bean developed using EJB 3 annotations. I am going develop the new entities in GORM. So, how can I reference/use the User entity from within the GORM entities?

I have J2EE EJB2 Session bean and EntityBean application. I would like to migrate EJB2 Session beans and Entity Beans to another working Grails application. Kindly let me know the migration steps