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Janino is developed or distributed by Arno Unkrig and is licensed as freeware. An embedded Java compiler that compiles expressions or scripts on-the-fly. Janino is a compiler that reads a Java expression, block, or source file, and generates Java bytecode that is loaded and executed directly. It is not intended to be a development tool, but an embedded compiler for run-time compilation purposes, such as expression evaluators or "server pages" engines like JSP.
Properties
The major design goal was to keep the compiler small and simple, while partially sacrificing completeness. I don't like the idea of carrying around huge libraries for simple applications. See Parser for the list of implemented and missing language features.
When do you need an efficient expression evaluator?
Say you build an e-commerce system, which computes the shipping cost for the items that the user put into his/her shopping cart. Because you don't know the merchant's shipping cost model at implementation time, you could implement a set of shipping cost models that come to mind (flat charge, by weight, by number of items, ...) and select one of those at run-time.
In practice, you will most certainly find that the shipping cost models you implemented will rarely match what the merchant wants, so you must add custom models, which are merchant-specific. If the merchant's model changes later, you must change your code, re-compile and re-distribute your software.
Because this is so unflexible, the shipping cost expression should be specified at run-time, not at compile-time. This implies that the expression must be scanned, parsed and evaluated at run-tim...
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