Mod Perl or Servlets?

A nameless submittor dropped this in my inbox: "I've heard people comment that Java Servlets are better than Perl CGI scripts. I've also heard the counter comment that while Java Servlets beat Perl, Mod Perl beats Servlets. I don't want to start a flame war, but I'm like to see the meat of this debate. Which is the better tool for server side web development? This is an area I'm about to get into and I'd like to see the pros and cons of each." I won't comment, if I did it would show my obvious Perl bias.

Comments

(ker-thump) Another log for the fire

[h2odragon]

I don't think anybody's mentionioned Python yet. Without extensive knowledge of the other alternatives, all I can say is that with a little care PyApache works for me. It's much like usual CGI in use, with some tricks like a dictionary for each Apache child process.

There's a different implementation of the same idea (embedding the python interpreter) called httdapy, I think, that's a little deeper into Apache interface-wise; I seem to recall it would work with Zope, too. That project is a "web application server" done in Python, if you haven't heard of it yet.

Two Different Tools For Two Different Uses

[marvinx]

Yes, you can certainly build interactive, dynamic web sites with both servlets and mod_perl. But to correctly build the site, you have to look at the scope of the site.

For quick and dirty sites, and if you already love Perl, then mod_perl is fine (personally I think PHP is easier). For sites that have a very limited scope, and for those which code maintanence does not matter, go ahead and pick a scripting language you are comfortable with. The whole point of those scripting languages is to enable rapid development. mod_perl allows you to take the rapid development to a web server.

If your application is large, or needs to scale, you will need to engineer the site, not just hack/script it. Today's extensive interactive sites need to cope with thousands of users and millions of hits. True, mod_perl will handle it as far as execution is conserned, but a n-tier, engineered application will create a better solution.

For those n-tier type applications, servlets are only part of the solution.

In a true n-tier web application, you will see many partitions emerge. Some of those partitions are

• client
  
• presentation
  
• business logic
  
• data
  

You will also see that servlets (and Java Server Pages) only fit in the presentation layer. To create a scalable application, you will want to abstract the business logic from the presentation. There are many solutions for business logic, and the Java universe promotes EJB.

The point is that to correctly choose a development environment, look at the scope of the application. If it's large, it must be correctly engineered, and a true OO language such as Java has a lot of advantages going for it. Those advantages include architectures such as servlets, JSP, fast server side VMs, rich class heirarchy, EJB, and support for latest XML/XSL technologies.

mod_perl tip

[Matts]

I work purely with mod_perl, so I won't disservice you with biased rumblings of how I think mod_perl is better - follow the advice of another poster here: Pick whichever tool your company/team has more experience with, and feels most comfortable working with. That's the only decision that should matter. Good perl people are expensive (as are good Java people - but the perl ones are harder to find/employ) though.

My tip is simply if you go the mod_perl route, please don't pick the no-brainer Apache::Registry route (this is a CGI-emulation mode). It will just in the long term cause you more troubles than it's worth. If you're working on an application complex enough to require choosing between either mod_perl or servlets then it's large enough to sit down and design it well. First design it without even thinking about the language: Think objects. Then work that into mod_perl. And use the mod_perl API to the full - there are some very cool things in there, like the $r->notes and $r->pnotes methods.

Also, mod_perl is far more than just a way to develop applications. You can do anything you can imagine to the actual Apache server with mod_perl - which makes it an indispensible tool for sysadmins. Witness Randall Schwartz's recent web techniques column on stopping naughty IE5 offline downloaders from sucking all available bandwidth, all done in mod_perl. (may not be available on stonehenge.com yet - try the mod_perl mailing list archives).

Finally, buy some books:

"Writing Apache Modules in Perl and C" by Doug MacEachern and Lincoln Stein. Excellent guide to everything mod_perl.

"Object Oriented Perl" by Damian Conway. Superb guide to doing things right the OO way in perl.