Thoughts on agile software development
The blog posts on the FreshMarker template engine pursue several goals. On the one hand, the posts should of course entertain their readers. On the other hand, they also serve me to focus and document my ideas on various aspects of the implementation. One very interesting topic in this post is the management of variables within the Template Engine.
I am pleased to announce the release of FreshMarker 1.9.0. The version includes some new features and improvements. The library is now available on Maven Central. And for all those who like a cheat sheet, there is now one available here.
A wonderful achievement of agile software development is, that new features are implemented when they are needed and not before. It took a long time for the built-ins left_pad and right_pad for padding text to be implemented, but now they are finally here.
The FreshMarker Template Engine works with an interpolation system that only takes the type of a variable into account at evaluation time. This approach makes the use of variables in FreshMarker very flexible, but occasionally leads to runtime errors. These can be avoided if the type of a variable can be checked beforehand.
The FreshMarker Plug-In Mechanism was one of the first features to be realized for the template engine. The idea behind it was simple. With a proper plug-in mechanism, a new feature can be easily realized and integrated and if it fits the core functionality, it stays in FreshMarker. Otherwise it becomes an independent plug-in. This is how FreshMarker File, FreshMarker Money and FreshMarker Random were created. It also created the internal FreshMarker support for Version, Locale, Year, MonthYear, MonthDay, Duration, Period and some other classes.
Whitespace in a template engine like FreshMarker’s is fundamentally different from the rest of the characters outside of it’s language constructs. A considerable amount of whitespace and line breaks are only used to ensure that the structure of the template remains comprehensible to the author.
A further step on the way to static templates is the automation of their creation. A Maven plugin can be used to convert the FreshMarker template sources into Java source code. Although there are now more modern build tools, Maven is still used in many projects. The first task of the Maven plugin should be the validation of template sources.
As soon as the handling of optional values is built into FreshMarker, another interesting feature appears, which could be added with tiny changes. It was implemented in three steps, with the next step only becoming apparent once the previous step had been implemented. The whole thing started with the fact that empty optionals should be processed slightly differently than null values.
Agile software development is characterized, among other things, by the fact that features are developed on demand. This is one of the reasons why some features are not available in FreshMarker or are only added very late. Examples of late additions are the Include- and Import-Directives and the support of the StringBuilder and StringBuffer data types. For the former, the use case was not planned at the start of development and for the latter, support was simply forgotten. Another forgotten data type is the Optional class, which is now finally to be supported.
When updating some libraries that use FreshMarker, I was a bit surprised. The Hamcrest Matcher Generator library was still using Freemarker and also the library has never been published on Maven Central. Two things that should be fixed as soon as possible.