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Script JavaBeans with the Bean Scripting Framework

Add scripts to your JavaBeans or JavaBeans to your scripts

By Mark Johnson, JavaWorld.com, 03/17/00

The Bean Scripting Framework (BSF) is one of the more interesting Java offerings available free at IBM's alphaWorks site (see Resources). BSF lets Java programs run scripts written in other languages and also allows other scripting languages to use existing Java classes. If you have useful scripts written in Python or Perl, for example, or have some useful BasicScript program you don't want to reimplement in Java, BSF will let you call that script from your Java program. BSF can also do the reverse, letting you use Java facilities and existing classes from your scripting language. BSF currently supports interoperability between Java and the various languages that appear in Table 1. The documentation shipped with BSF indicates that support for more languages is in development. All of the languages listed are freely available, though the restrictions for commercial use vary. Downloading information for each language is available from the documentation shipped with BSF.

Some languages (as indicated in the table below), run only on Windows 95 or later, because the ActiveX scripting technology on which they rely is limited to Windows. The rest of the languages run portably on any system that has a Java Virtual Machine (JVM), since they are written in portable Java.

Language	Description
BML	IBM's Bean Markup Language
JScript	Microsoft's implementation of JavaScript. Windows only.
Mozilla Rhino	Netscape JavaScript, available from Mozilla. Written in Java.
NetRexx	IBM's Java implementation of the Rexx editor language. Written in Java.
PerlScript	ActiveState's Perl scripting environment. Windows only.
VBScript	VisualBasic scripting environment. Windows only.
Jacl	Java implementation of a large subset of Tcl.

JPython	Java implementation of Python.
LotusXSL	IBM/Lotus implementation of the XSL language

Scripting languages supported by BSF

In this article, I'll explain why you may want to use BSF in your application, whether you're writing it in a scripting language or in Java. You'll see how to use an existing Java class from a script written in a scripting language. Then, you'll see a Java program that can evaluate scripts written in other languages and can use the results. Finally, I'll explain some of the ways IBM is using BSF in its own products.

Why scripting?

I've always found Java's lack of an eval statement to be a bit disappointing. Of course, I understand the reasons for leaving it out. The JVM is big enough without building a Java compiler into it, and eval would add another level of complexity to security control. Besides, a lot of the things I'd like to do with eval can be done more efficiently, elegantly, and type-safely with class loading. But still, sometimes I just want to be able to evaluate an expression. Is that too much to ask?

Since I was born and raised on Unix, my head is filled with arcana about various scripting languages I've learned. I've written a lot of useful scripts over the years, some of them quite complex. (I once wrote a compiler-compiler in Perl. Don't ask.) I'd love to be able to use my scripts from Java, but doing so by way of System.runtime() is what I call "3-I": inefficient, inelegant, and icky.

 

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