Bye Bye Blogger

At last, I have moved my blog to my own domain.
Please find it at http://blog.ckkloverdos.com.
The relevant feed is at http://blog.ckkloverdos.com/feed/.

On Handling Dependent Resources - The Ensure/Create/Test Pattern

Recently, I had to restructure some resource handling code. The case that I had some resources A, B, C, ... and each one depended on some other in order either to be created or to function properly. So I had to devise a way to handle the dependencies and make sure that whenever I used a resource, all its dependencies are met.

I will use a simplistic example to make things clearer. Let's say we have resource A, which depends on resource B, which in turn depends on resource C. A is created using B and B is created using C. Our code always uses A directly, so we need to make sure that B and C have been created before using A.

My second approach to the solution is a lazy, bottom-up one. Before using A, I need to ensure that it is functioning correctly and of course lazily create it at some point. Also, I assume that we can always have some test functionality to make sure that A is "alive". For example, for a DB connection we can always issue some test SQL statement (select 1 from dual is common among Oracle developers). In the previous statements, please notice my italics on the three notions: ensure, create, test. So here are my findings:

Client code that uses A:

ensure(A)
  ...do something with A...

The backbone routines:

def ensure(A):
  if A is null:
    create(A)
  test(A)

def create(A):
  dispose(A)
  ensure(B)
  B.create(A)

def test(A):
  ...

Notice that I am also using one more routine, namely dispose. Its role is to safely dispose a resource, meaning that it takes care that the resource is not null, it properly handles exceptions and so on. Of course, as you can understand, there are a lot more details for a production-ready code and the routines admit variations...Also, in the generic case, we may have a graph of dependencies...

This is how I came to the programming pattern, for which I just chose the name in the title. As I wrote above, this is my second approach. The first was a top-down one . But I am not going to give it here....

On tools [mytex]

I have always been fond of tools that makes life easier....

I recently needed to recompile one of my papers in Greek and mytex did - once more - its job perfectly well.

I made it during my stay at the National Hellenic Documentation Center in order to handle masses of LaTeX-based (!!!) documentation I had produced there.

mytex helps one with the parsing of LaTeX files written in mixed greek and english. It can automatically insert proper babel commands for the language switches.

Spring 2.0.1 and BEA WebLogic Server 9.2 Integration

Spring brings the power of POJOs to BEA's server

Spring 2.0.1 and BEA WebLogic Server 9.2 Integration by Andy Piper and Eric Hsiao, Rod Johnson, Chris Wall -- WebLogic Server 9.2 provides a platform for enhanced management, ease-of-use and scalability of Java applications. The Spring Framework enables a simpler, POJO based, approach to Java EE development without sacrificing the power of the platform. This article describes the synergy of these two systems, and introduces the Spring on WebLogic kit.

First Post

Just for historical reasons...

More will come soon. For the moment, take a look at my space: http://ckkloverdos.com