Monthly Archives: January 2012

Leiningen and standalone clojure programs

Hacking away at various clojure-related stuff lead me to start using Leiningen. “Lein” is a build tool similar to Maven (and interoperates in fact…) to help you concentrate on coding.

At some point in the day’s coding I wanted to run my code standalone instead of in a REPL. I needed a main entry point to the various algorithms I was writing that was outside of unit tests, so I decided to use the “lein run” command to do it for me.

In order to get a program running via lein using a main method, you have to provide the namespace of the class to run. If you want a JAR produced that’ll have the Main-Class declaration in your MANIFEST.MF you also need to add :aot and :main namespace.here to your project.clj AND add (:gen-class) in the (ns) call of your desired .clj holding a -main method. Phew!

To re-cap, then:

  • To run a .clj that has a -main method/function declared, add (:gen-class) to its (ns) call and then run lein run namespace.here
  • To produce a JAR with lein, do the above and add :aot and :main namespace.here to your project.clj then run lein compile && lein uberjar

Learning Programming Languages

I’m a hacker. Hackers like learning. Every year I try and learn a new programming language: it helps me to get better at thinking, I learn new ways of programming, it’s fun and I keep abreast with technology.

In picking up a new language I run through certain easy problems that help me tackle the necessities of learning the APIs for a particular language and picking up habits (both good and bad) that are idiomatic of the chosen tongue. So, I decided to document what I do to learn to code. You can read it on my wiki.

Modern Service Oriented Architecture: the basics

Just some of my notes on looking over SOA related theory.

What is “SOA”?
Service Oriented Architecture is a means of exposing business services
separately from their platform and codebase in order to provide local
and/or remote invokation of said services through abstracted data types
and signatures.

Put simply: SOA allows you to talk to alternate platforms by removing
the bespoke or language-specific features and data types to a
higher/specified representation providing interoperability between
platforms without the need for their awareness of eachother.

As a real world example, an organisation can provide interoperation
between legacy and new systems by abstracting the manner of how they
talk and the underlying content: new code can use technologies like XML
to define the data and the corresponding types and the two systems can
work together through that abstraction. This scenario is commonplace
among business where different streams are responsible for systems and
so a common format for data interchange is necessary to allow the two to
co-exist separately.

SOA also provides a more modular approach to service integration: if a
web service can “proxy” requests from one system to another, the two can
change independently without the need for related changes to the
services themselves. Such a scenario – one of proxying – can encourage
an ecosystem of services allowing each to communicate with seemingly
unrelated counterparts through a common set of data types and methods.

Benefits of SOA
Typically, the “promises” of SOA are numerous.

SOA allows for system agility
As aluded to previously, the ability for bespoke systems – those written
for specific purposes in a language of choice – to communicate with each
other allows for greater flexibility and scalability with an
organisation’s data. For example, if you can have your sales systems
talking to your suppliers through an aggregation service to warn of
unusual sales volumes, out-of-stock items and so-on, you can better
support the volume of a growing business and provide real-time response
to customer needs.

Consider an organisation where a sales system cannot speak with the MI
to ascertain whether a customer on the phone holds an account with you.
Crazy, no? In scenarios like this where legacy, decades-old and
difficult to support systems hold the key to sales success but are the
hindrance to it, SLA can be leveraged to quickly and easily have the two
communicating and providing front-line departments with the information
they need.

SOA can encourage innovation
In the post-Google era, notions of service “mash-ups” are commonplace.
These newfound, new-age businesses popularised the developer by
harnessing open source technologies and building public-facing APIs: all
built on service oriented architecture. They encouraged interoperation
between seemingly unrealted entities which built a platform for
innovation and a revolution in the software industry.

If you reduce this scale and manage to accomplish this very nature
within an organisation, then new products and alternatives to existing
ones spring from innovative and organic attitudes from developers and
system integrators.

Ouch

Don’t sudo telinit 6 all willy-nilly in a terminal without thinking twice. I just restarted this server accidentally! Very ouch.

I’ve decided to have this alias in my .bashrc:

alias telinit="echo Do you really want to telinit this server?!"