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From: Wes Wannemacher <wesw@wantii.com>
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To: "Struts Users Mailing List" <user@struts.apache.org>
Subject: Re: How do my Actions get to Hibernate so they can persist my
 objects?
Date: Sun, 8 Mar 2009 20:46:00 -0400
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On Sunday 08 March 2009 20:07:26 Peterus Greatus wrote:
> I am hoping someone can paint a picture for me as I do not really
> understand the relationship between Struts2 + Spring + Hibernate. The
> reason I know about Spring is every book or tutorial I can find with
> Struts2 and persistence uses Spring.
>
> Background is my last programming in Java was 9 years ago with Struts =E2=
=80=93 I
> really enjoyed it and now I=E2=80=99ve to write a new web app so I chose =
Struts2.
> Over the past two weeks I=E2=80=99ve spent more time learning Hibernate, =
Ant,
> something called Maven, I bought a Struts book that use Maven and now I=
=E2=80=99ve
> to understand something called Spring!

Spring is not as hard as it appears. The Spring libraries are dauntingly bi=
g,=20
but in reality, the core of spring is actually quite easy to understand, yo=
u=20
just have to wrap your mind around Inversion of Control. It will come=20
naturally if you've used it before, but if Spring is your first venture, ba=
re=20
with it a bit, you'll be glad you did.

>
> I thought this was going to be easier than Struts 1 with JDBC and writing
> my own SQL.
> It=E2=80=99s not programming its learning frameworks!
>
> Anyway back to my question. I understand Struts2 quite well now, I can ma=
ke
> forms and produce success pages. Everything is transient. I now need to a=
dd
> some persistence so I am using Hibernate (as its seems to be the bees
> knees). After much reading of a large book about Hibernate I understand h=
ow
> that works=E2=80=A6.
>
> What I don=E2=80=99t get is how my Struts2 action talks to Hibernate.
> I've added a Listener to my web.xml for Hibernate, but not sure when that
> is used.
> I have a HibernateUtil that creates a SessionFactory which I understand is
> used for transactions with the database. I want that guy to start when my
> web app is started in Tomcat so all I have to do is go to him to make a DB
> connection.
>
> But how do I get a session from the factory within a Struts2 Action? It
> seems odd to put code into each Action to do this. I imagine people more
> clever than I solved this problem.

In a way, you are answering your own question about how Spring fits in...=20
Struts does not concern itself with things such as database transactions (o=
r=20
any transactions). In most applications, you'll find that you "wire" up thi=
ngs=20
like a Spring service into your application, then by way of the Spring plug=
in,=20
your action will automagically retrieve an instance of the service through =
a=20
setter on your action. More below.


>
> I figure this is where Spring comes in with Inversion of Control or some
> other concept I=E2=80=99ve started reading about.
>
> I've read this guy
> http://struts.apache.org/2.0.11/docs/struts-2-spring-2-jpa-ajax.html
> This PersonService object seems like a hokie solution. Do I make a Service
> for each object I want to persist? Thats a bit mad. I have to define all =
of
> these services in Spring too? I=E2=80=99m already defining a bunch of Hib=
ernate
> mapping xml file for each object I want persisted=E2=80=A6 I'm writing mo=
re XML
> than Java.
> Also how come I=E2=80=99m defining the database connection details in Spr=
ing when I
> have them in my hibernate.cfg.xml ?

=46irst off, rather than making a "service," think of it as a DAO. This is=
=20
actually a good pattern to follow. On top of that, if you're pretty handy w=
ith=20
the latest Java features, you can build a DAO pretty easily using generics.=
 I=20
have a full example similar to the one you mentioned available here -=20

http://code.google.com/p/struts2inpractice/source/browse/#svn/trunk/ch04ex01
=20
The difference between my example and the one you referred to is that I use=
 a=20
generic dao. In fact, this will sound like a shameless plug for my book, bu=
t I=20
spend the first couple of chapters trying to explain how all of these piece=
s=20
fit together.=20

>
> I think what is lacking is an explanation of why certain things are done
> the way they are (it=E2=80=99s supposed to be a tutorial=E2=80=A6for begi=
nners). Even those
> tutorial writing guys over at RoseIndia don't seem to have nailed this.

The reason things are spiralling the way you noticed is that each framework=
=20
makes an attempt to cover a particular design pattern. In the case of=20
applications like you mentioned, you have something similar to the followin=
g -

Struts2->	Spring->	JPA or Hibernate
MVC		IoC/DI		Database Persistence

There are significant advantages to adopting solid design patterns to solve=
=20
problems. The learning curve can be steep, but you reap the benefits of=20
reusability, testability and stability.=20

>
> I understand Tomcat, Web Apps with Servlets & JSPs. Spring seems to wrap
> itself around Hibernate. Tomcat somehow makes Spring go, which in turn do=
es
> the Hibernate bit. I don=E2=80=99t see how my Actions in Tomcat get to th=
e database
> via Hibernate any easier with Spring.

The piece you're missing here is that Spring services can easily be wired i=
nto=20
your actions. If you have a bean named springBean defined in your=20
applicationContext.xml, then have the spring plugin installed in your strut=
s=20
app. Then, you have a setter on your action called=20
setSpringBean(SpringBeanInterface sbi), the plugin will see the setter and=
=20
give you a copy of the service. It's pretty slick and saves you quite a bit=
 of=20
time and exception handling.

>
> I read this guys post here
> http://mail-archives.apache.org/mod_mbox/struts-user/200709.mbox/ So I=E2=
=80=99m
> pretty certain I need to be using Spring.
>
> To me it seems like Spring is a pre-requisite for Java development. Maybe=
 I
> need to be drinking the Spring Kool-Aid.

The need to use Spring really increases proportional to the size of the=20
project. It is definitely another layer of complexity, but it is worth it i=
f=20
you are building an application to scale up over time. At the same time, th=
e=20
more you use it, the more you'll find it helping you. The wiring of=20
dependencies is just one piece, there are also quite a few other helpful=20
advantages, AOP, transaction management, and mock objects to name a few.

Again, this will seem like a setup for my book, but I am currently writing =
it=20
with the intention to introduce people into modern development techniques l=
ike=20
this. I take the approach that Struts is a common piece, but that most=20
applications will have the need to utilize other libraries such as Spring,=
=20
Guice, EJB or any number of other helper frameworks.=20

=2DWes

=2D-=20

Wes Wannemacher
Author - Struts 2 In Practice=20
Includes coverage of Struts 2.1, Spring, JPA, JQuery, Sitemesh and more
http://www.manning.com/wannemacher


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