alibaba/qlexpress

QLExpress is a scripting engine built in Java that lets you run small programs or business rules at runtime without recompiling your application. Instead of hard-coding logic like pricing rules, discount calculations, or approval conditions into your Java code, you write those rules as short scripts that QLExpress evaluates on the fly. This is useful when business logic changes frequently and you want to update rules without redeploying the whole application. The project was created at Alibaba around 2012 to handle the kinds of flexible calculations that arise in large e-commerce platforms, things like high-precision math, boolean rule combinations, and custom formula evaluation. It has been widely used across Alibaba's internal systems and was open-sourced so that other teams could use it too. The scripting syntax is loosely similar to Java and JavaScript. You can write loops, conditionals, define functions, create objects, and call methods on Java classes. Because it is a weakly typed language, you do not need to declare variable types. The engine is thread-safe by design, caches compiled scripts for reuse, and is packaged as a small 250KB jar file that runs in standard Java environments including Android devices. Safety controls let you restrict what scripts can do, for example blocking access to dangerous system calls or preventing infinite loops. This makes it practical to run scripts submitted by end users or non-developer staff without giving them unrestricted access to the underlying system. A major version 4.0 is in beta at the time of this writing, described as a significant rewrite with improved usability. The project is actively maintained and accepts contributions. The full README is longer than what was shown.