[Tech] Distributed SCM: Playing with Repos

As some may have noticed, I migrated nearly all my projects in the last year from Subversion to Mercurial (and GIT). Step by step, as I am rather conservative with changing to new technologies, particularly when they are at the heart of the project. And changing the SCM is sort of a surgery on the open heart.

However, after nearly a year of experience I must say, SCM was (for me) never easier and more enjoyable than with distributed SCMs, particularly with Mercurial. Excellent documentation, easy and straightforward to use. Yet these days I was asking myself: If I would have to name one outstanding feature that would convince me to change from a centralised system like Subversion to DSCM, what would it be?

The answer might be surprising, but for me it is clearly this: No headache and fear when working with the repository any more. What do I mean with that? Well: I was never a Subversion guru and everytime I needed to do an operation I did not do very often (branching, merging) I was sweating. Should I press the button, am I making a mistake? What exactly do these options mean in the SVN client? Did Eclipse now mess up the local copy? Should I commit? After all, you are always working with the repository. If you mess up, you have a problem, and all team members with you. Not a nice procedure.

But with a DSCM there is no master repository, hence in case of doubt I make a clone, play around with the clone. Should I mess it up, I delete the clone and nothing happened. If everything is fine I push the results. This is for me personally the most essential feature of systems like Mercurial. I can play around even with esotherik plugins and features without the fear to destroy anything. This also makes learning for new users way easier.

What is your opinion?

[Pub] Best-Practice Book and the New Year

Some of you might already have noticed, that we were not very active in blogging the last months. The reason is, that (most of us) were heavily involved in finishing our "Best Practice Software Engineering" book that will be available Feb/March 2010. The publisher is Spektrum Akademischer Verlag (Springer), the book is in German.

It was a lot of work and required most of our publishing energy. I believe the result is good and I hope that it will be useful for some of you.

A detailed description of the book can be found at the publishers website.

If you are as enthusiastic as we are, you can even pre-order it via Amazon ;-)

So, for now, I want to thank all readers of our Blog, hope you had a successful 2009 and wish you all the best for 2010. Looking forward to comments from you about our book and upcoming blog posts.

[Tech] Simple Java Template Engine

Template engines are widely used in Web Frameworks, such as Struts, JSF and many other technologies. Apart from classical Web Framework, template engines can be very useful in integration projects. In an actual integration project that deals with a lot of XML data exchange, I discovered the Java Template Engine Library FreeMarker. This Open Source Library is a generic template engine in order to generate any output, such as HTML, XML and any other user defined output based on your given template.

"[...]FreeMarker is designed to be practical for the generation of HTML Web pages, particularly by servlet-based applications following the MVC (Model View Controller) pattern. The idea behind using the MVC pattern for dynamic Web pages is that you separate the designers (HTML authors) from the programmers. Everybody works on what they are good at. Designers can change the appearance of a page without programmers having to change or recompile code, because the application logic (Java programs) and page design (FreeMarker templates) are separated. Templates do not become polluted with complex program fragments. This separation is useful even for projects where the programmer and the HTML page author is the same person, since it helps to keep the application clear and easily maintainable[...]"

I think HTML is one application area of FreeMarker. Consider 3rd party systems providing APIs consuming XML data or their own data structures. Construct their data format in the code is a grubby approach and furthermore the code becomes not maintainable. Using such a library you can manage your data exchange template outside your code and produce the final data by using the template engine. I see such template engines as classical transformers as in an Enterprise Service Bus:

In the above exmple you see, that you can use placeholders in your template files, which will be replaced by the real data when the transformation takes place. FreeMarker provides enhanced constructs such as if statements, loops and other stuff which can be used in your template files.

Template engines are often used in Web Frameworks, but the usage of template engines is also very useful when you must produce specific output for other systems.