Overview

The xweld-expression module provides a small but powerful standalone module for representing Boolean or mathematical expressions, and parsing them from Strings that can be evaluated into either a Boolean or Numeric result. While there are several other Java expression languages available – SpEL, OGNL, MVEL, and JBoss EL, to name a few – the xweld-expression module is extremely lightweight and provides only those primitives typically required by the <xweld/> suite of tools. Because of its simplicity, it is extremely easy to set up and use.

One primary motivation for the expression class library is to support Permissions in xweld-security that use a context when they are evaluated. For example, expressions support the notion of context-sensitive permissions, to control enabling or disabling GUI controls according to a user's metadata, such as that user's region and product set. That said, xweld-expression is based on a technology-agnostic API allowing other expression language implementations to be integrated should the need arise in your application.

The xweld-expression language supports the following functionality:

  • Double or Boolean evaluation results
  • Expressions containing quoted String values and numeric literals and lists
  • Expressions containing Boolean relational operators, such as >, < ,=, & and |
  • Expressions referencing fields or methods of a context object passed at evaluation time using reflection
  • Expressions supporting parameters supplied at evaluation time
  • Expressions checking whether a field, parameter, or literal is contained in another list of values

The module documentation is available here:

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