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Alex Miller from BEA Systems gave a presentation on domain specific languages at the St. Louis JUG yesterday.

Alex started by showing examples of several DSLs: regular expression, SQL, chess notation, needlework pattern notation, etc.

Some of the common properties of all of the DSLs shown are: compact, concise, having an implied context, assumption of domain knowledge, etc.

He then showed the pros and cons of introducing a DSL into a product. Both the pros and cons are consequences of the shared properties of DSLs.

He then introduced ways by which a DSL is implemented:

• through what Martin Fowler calls Fluent Interfaces
• using a scripting language like the BeanShell
• writing a parser yourself (either by hand or using a parser generator like Antlr)

Examples and implementations of a DSL for chart generation using the JFreeChart library in all three shades are shown.

There are some memorable quotes from the talk:

• If you look at a fluent interface from an API design point of view, they are terrible APIs
• (Of writing a parser, Terence Parr said) why do it by hand in five days when you can automate it in three years
• JavaCC has gone through too many hands in the past 10 years before landing in the spot on Java.net, while Terence has been doing nothing but Antlr during the same time. I wouldn't recommend JavaCC at this point

I started a mini-debate during the Q&A portion of the meeting by asking the "Spring+Hibernate" vs. "Java EE 5/EJB 3" question. It went off on multiple tangents (Struts being legacy, AJAX being tricky, etc.) but I did see one committed Hibernate believer in Kyle Cordes and one committed Spring believer in Jeff Grigg. Jeff Brown pointed out (when I asked him before the meeting) the two are not mutually exclusive: you can use both Spring and Hibernate in a Java EE 5 container, and your EJB 3 implementation may very well be Hibernate itself.

But Web 2.0 (Dojo, Prototype, AJAX, etc.) is the future.