Script JavaBeans with the Bean
Scripting Framework - JavaWorld March 2000
Tutorial Details:
Script JavaBeans with the Bean Scripting Framework
Script JavaBeans with the Bean Scripting Framework
By: By Mark Johnson
Add scripts to your JavaBeans or JavaBeans to your scripts
he 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.
I'd also like to be able to make my applications extensible by adding scripting languages to them, so users can add the functionality they want. Extensibility is a key requirement for all of the servers with which I've worked. A venerable and still-popular Web server extension mechanism is CGI (Common Gateway Interface). CGI allows any program, written in almost any language, to masquerade as a Web page, providing dynamic content. But CGI can be very inefficient: common implementations of CGI start a new process for every request. Server developers began adding embedded scripting languages to their server offerings, allowing their customers to extend and customize servers without the overhead of individual processes. Modern servers, such as Apache, provide an API or other facilities to let users create extensions in virtually any scripting language.
All of the situations described above can now be addressed in Java, by way of BSF. As I mentioned earlier, BSF allows Java programs to evaluate and access results from scripts written in other languages. BSF also does the reverse. With BSF, scripts written in those other languages can create, manipulate, and access values from Java objects.
Let's start our tour of BSF by using it to call Java code and using Java classes from some common scripting languages.
Using Java code from a script
One of the ways languages, and particular implementations of languages, differ from one another is in their relative ease of support for various features. For example, writing screen resolution-independent GUI elements may be easier in languages such as Java and the Tool command language's (Tcl) Tk extension, with their customizable layout managers, than in languages such as BasicScript or JavaScript, which have little or no dynamic layout control. BSF provides the scripting languages it supports with access to all the features of Java classes and the existing Java code base.
In the examples below, I demonstrate how to use BSF to create a simple Java user interface from JavaScript and Jacl. Then I'll show you how to use an existing Java dialog box to get user data from a Jacl script.
Ave, mundus!
Listing 1 shows a simple example for using BSF to create Java objects in Jacl. The script creates a simple frame containing a single button labeled "Ave, mundus!" (The label means "Hello, world!" in Latin. This spring I'm visiting two Latin countries, France and Italy, so I'm brushing up.) Clicking the button causes the script to exit. Listing 1. The "Ave, mundus!" program in Jacl
001 package require Java
002
003 set f [java::new java.awt.Frame "Jacl running in BSF"]
004 bsf addEventListener $f "window" "windowClosing" "exit"
005 set b1 [java::new java.awt.Button "Ave, mundus!"]
006 bsf addEventListener $b1 action {} { quit "Jacl says goodbye" }
007
008 $f add $b1
009 $f pack
010 $f show
011 $f toFront
012
013 proc quit { message } {
014 puts $message
015 exit 0
016 }
Line 2 in Listing 1 is a standard Tcl command that tells Jacl to load the java package. This statement creates a number of new commands in the Jacl interpreter, allowing Jacl statements to manipulate Java objects. BSF then allows Java objects and Jacl scripts to "talk" to one another via events.
Line 4 uses the standard Jacl java::new command to create a java.awt.Frame and associate it with the variable f .
Line 5 instructs BSF to add an event listener to the frame. (The following discussion assumes you understand Java 1.1+ event listener interfaces; if you don't, or if you need a refresher, see Resources below.) BSF creates a window event adapter object whose sole purpose is to listen for a windowClosing event to occur on the Frame object $f . When a windowClosing event occurs, the adapter object evaluates the Jacl expression "exit" , causing the program to exit.
The general syntax that tells BSF to add an event listener to an event source is:
bsf addEventListener eventSource adapterType filter handlerScript
The event listener is an object, called an event adapter , that evaluates the handlerScript whenever an event of a particular type occurs on the eventSource . The event adapter classes for standard Java event types are defined by BSF and come with the distribution, but you also can define new adapters for custom event types (see the BSF documentation to find out how). The adapterType is the type of event, and the filter is the name of the Java event interface method handling that event.
Line 6 creates a Button with the label "Ave, mundus!" and line 7 instructs BSF to evaluate the given Jacl script { quit "Jacl says goodbye" } whenever an actionEvent occurs. Since there's only one method in the ActionEventListener interface, the filter argument is empty.
Lines 8 through 11 correspond to method calls on the Frame object $f . The ability to call Java methods directly from Jacl, shown here, is provided by Jacl and the java package imported in line 2. Each scripting language has a slightly different way of calling methods on JavaBeans created in that language; see the BSF documentation for the description for the language you're using.
Lines 13 through 16 in Listing 1 form the definition of the quit procedure called by the event listener defined in line 6. This is the script that's evaluated when the user pushes the button.
Figure 1 shows the window that results when running the sample file hello_world.jacl (you can download the sample code and scripts free; see Resources ). To run BSF directly from the command line, be sure the Jacl and BSF jar files are in your classpath, then simply issue the following command to make sure the sample file is in your current directory:
java com.ibm.bsf.Main -in hello_world.jacl
Figure 1. The result of Listing 1
Reimplementing the same script in JavaScript is simple. The reimplementation appears in Listing 2 below.
Listing 2. "Ave, mundus!" in JavaScript
001
002 f = new java.awt.Frame("JavaScript running in BSF");
003 bsf.addEventListener (f, "window", "windowClosing",
004 "java.lang.System.exit (0);");
005 b1 = new java.awt.Button("Ave, mundus!");
006 bsf.addEventListener(b1, "action", null, "quit('JavaScript says goodbye')");
007
008 f.add(b1);
009 f.pack();
010 f.show();
011 f.toFront();
012
013 function quit( s ) {
014 java.lang.System.out.println( s );
015 java.lang.System.exit(0);
016 }
The program looks so much like Listing 1 that it scarcely needs explanation. The two scripts really differ only in the syntax of function calls and in how they access Java objects. Rhino JavaScript uses Netscape's LiveConn
Read
Tutorial at: Click here to view the tutorial
Rate Tutorial: Script JavaBeans with the Bean
Scripting Framework - JavaWorld March 2000
View Tutorial: Script JavaBeans with the Bean
Scripting Framework - JavaWorld March 2000
Related
Tutorials:
 Scripting power
saves the day
for your Java
apps
Scripting power
saves the day
for your Java
apps
|
Deploy code
servers in Jini systems
Deploy code
servers in Jini systems
|
Boost Struts with
Boost Struts with XSLT and XML
|
Container-managed relations for the
21st century
Container-managed relations for the
21st century
|
Navigate data with the Mapper framework
Navigate data with the Mapper framework
|
JDBC scripting, Part 2
JDBC scripting, Part 2
Programming and Java scripting in JudoScript
Summary
JudoScript is a rich functional scripting language, and an easy and powerful general programming and Java scripting language.
JudoScript's power comes from its synergy of
|
Prova
Prova: A Language for Rule Based Java Scripting, Information Integration, and Agent Programming
|
Groovy, Java\'s New Scripting Language
Groovy, Java\'s New Scripting Language
When some Java developers hear about Groovy, their first reaction often is, as mine was, "Oh, no, not another scripting language for Java." We already have, after all, JavaScript and Rhino, Jython, Jelly, BeanShell,
|
A lightweight nonintrusive EJB testing framework
A lightweight nonintrusive EJB testing framework
Summary
This article presents a simple, easy-to-deploy framework that enables fine-grained tests to be run on the container, making it possible to develop and maintain Enterprise JavaBeans components usin
|
Request bean ver. 1.5
Java bean allows you to proceed GET/POST requests to the specified host (cgi-script/servlet). So you can for example obtain contents of some page and use extracted information in your own jsp page.
|
Testing Your Enterprise JavaBeans with Cactus
Enterprise JavaBeans provide many advantages. But each server-side/back-end developer knows that development of EJBs is sometimes painful, time-consuming, and requires a lot of patience while creating assembly descriptors, application-server-specific conf
|
Struts, JavaServer Faces, and Java Studio Creator:
The Evolution of Web Application Frameworks Sun Microsystems' Craig McClanahan, the creator of the Apache Struts Framework, co-specification lead for JavaServer Faces 1.0, and prime architect for Sun Java Studio Creator's new release, explains all three.
|
What is Persistence Framework?
What is Persistence Framework?
What is Persistence Framework?
A persistence framework moves the program data in its most natural form (in memory objects) to and from a permanent data store the database. The persistence framework manages the
|
Open Source Web Frameworks in Java
Open Source Web Frameworks in Java
Open Source Web Frameworks in Java
Struts
Struts Frame work is the implementation of Model-View-Controller (MVC) design pattern for the JSP. Struts is maintained as a part of Apache Jakarta project and is open
|
Jakarta Struts Interview Questions
Jakarta Struts Interview Questions
Jakarta Struts Interview Questions
Q: What is Jakarta Struts Framework?
A: Jakarta Struts is open source implementation of MVC (Model-View-Controller) pattern for the development of web based applications.
|
developing a Session Bean and a Servlet and deploy the web application on
JBoss 3.0
developing a Session Bean and a Servlet and deploy the web application on JBoss 3.0
Writing Calculator Session Bean and Calling through JSP
Previous Tutorial Index Next
In this lesson I will show you how to develop a Calculator Stateless Session
|
developing a Session Bean and a Servlet and deploy the web application on
JBoss 3.0
developing a Session Bean and a Servlet and deploy the web application on JBoss 3.0
Writing Stateless Session Bean and Calling through Servlet
Previous Tutorial Index Next
In this lesson I will show you how to develop a Stateless Session Bean and
|
Beginner to advance guide to the Apache Struts
Beginner to advance guide to the Apache Struts
The Complete Apache Struts Tutorial
This complete reference of Jakarta Struts shows you how to develop Struts applications using ant and deploy on the JBoss Application Server. Ant script is provided
|
Struts Validator Framework Tutorial with Example
Struts Validator Framework Tutorial with Example
Struts HTML Tags
Struts Validator Framework
This lesson introduces you the Struts Validator Framework. In this lesson you will learn how to use Struts Validator Framework to validate the user
|
Understanding Struts Controller
Understanding Struts Controller
Understanding Struts Controller
In this section I will describe you the Controller part of the Struts Framework. I will show you how to configure the struts-config.xml file to map the request to some destination
|
|
|
|
