JEXL is a library intended to facilitate the implementation of dynamic and scripting features in applications and frameworks written in Java.
JEXL is a library intended to facilitate the implementation of dynamic and scripting features in applications and frameworks written in Java.
From the official documentation:
JEXL implements an Expression Language based on some extensions to the JSTL Expression Language supporting most of the constructs seen in shell-script or ECMAScript. Its goal is to expose scripting features usable by technical operatives or consultants working with enterprise platforms.
The library exposes a small footprint API - the core features fit in 3 classes and 10 methods - that can be used in various conditions:
- Scripting features:
- Your application lets (advanced) users evaluate or define some simple expressions like computation formulas.
- Module or component configuration:
- Your application has configuration files (eventually generated by a design module) consumed by the end-user module that would benefit from variables and expressions.
- When it would be convenient to use IOC but overall complexity doesn't require (or can't depend upon) a full-blown library (Spring, Guice...).
- Loose-coupling of interfaces and implementations or duck-typing:
- You have optional classes that your code cant consider as compilation dependencies.
- You have to integrate and call "legacy" code or use components that you don't want to strongly depend upon.
- Simple template capabilities:
- Your application has basic template requirements and JSPs or Velocity would be overkill or too inconvenient to deploy.
JEXL name stands for Java EXpression Language, a simple expression language originally inspired by Apache Velocity and the Expression Language defined in the JavaServer Pages Standard Tag Library version 1.1 (JSTL) and JavaServer Pages version 2.0 (JSP). JEXL 2.0 added features inspired by Unified EL. The syntax is now close to a mix of ECMAScript and "shell-script" making it easy to master by technical operatives or consultants. The objects exposed and their behavior obviously need to be documented though...
The API and the expression language exploit Java-beans naming patterns through introspection to expose property getters and setters. It also considers public class fields as properties and allows to invoke any accessible method.
JEXL attempts to bring some of the lessons learned by the Velocity community about expression languages in templating to a wider audience. Commons Jelly needed Velocity-ish method access, it just had to have it.
It must be noted that JEXL is not a compatible implementation of EL as defined in JSTL 1.1 (JSR-052) or JSP 2.0 (JSR-152). For a compatible implementation of these specifications, see the Commons EL project.
