Tag Archives: Juel

Expression Language Validation

We used juel as an expression language EL implementation in one our projects. The problem we had, was that we could not afford waiting for the expression to be checked at runtime. For example if you are accessing a pojo field, and that field does not exist, they you only know it in runtime.

To fix this, I created an extension and added a validate method. This method traverses the tree and checks all possible options to make sure the expression is valid with given objects.

I offered the new extention to the community, but they thought it is better to keep the Juel to minimum required to match the standard.

I am going  to publish as an extension to Juel in seperate branch. Maybe someone else also can make use of it. Not planned yet though.

MDA Approach for Card Scheme conversion

The idea is to use MDA approach for conversion of one card schema to the other one. The traditional way is to write java code field by field. What I suggested is to use MDA (Model Driven Approach) for the conversion. The idea is to define the model in a kind of object model, use XML to make the model and create the framework to execute the mode.

During the implementation I understood that usage of standard EL (Expression Language) would be very handy and I successfully tried Juel.

In this way, the conversion rules are much more meaningful and understandable. It is also possible to change them dynamically without recompiling.

There is only one important negative point and that one is type safety. Not all expression in Juel are checked against syntax in type of loading. My next task on this subject is to find how can I guaranty type safety, at least at the same level as java code.