Kyle Cordes: Scripting Your Java App

Fri, 10 Nov 2006 06:02:41 GMT

This month's St. Louis JUG meeting featured Kyle Cordes talking about scripting Java applications

"I attended one of Edward Tufte's classes," started Kyle. I know right away that I won't be able to get the PowerPoint for the talk at the end. Kyle did the presentation in Eclipse and showed code.

Kyle handed out a one page summary that contained all the main points of the talk in complete sentences and paragraphs. Since it's not very creative to simply copy that sheet of paper into this blog, I'll summarize the talk into bullet points.

History of scripting
Bean Scripting Framework (BSF)
BeanShell (JSR 274)
Groovy (JSR 241)
Java 6 scripting (JSR 223)
Demos
Rhino (Mozilla's Java based JavaScript engine)
"You won't get into trouble by using the scripting language in the JDK"
We have been very happy using Rhino to scripting an enterprisey application
It's surprisingly easy to add scripting support
What's a scripting language
- Dynamic typing
- Interpreted execution
- eval
Why script
- Configuration
- More important in commercial systems
- "Alternate hard and soft layers"
- modular & testable
- Users will use scripting to create incredible values
Kinds of scripting APIs
- Rules scripting
- Plugin scripting
- External scripting
Sandbox is very important (scripts shouldn't be able to see your app's internals)

Where Is My java.home?

Thu, 15 Jun 2006 01:06:07 GMT

From time to time, I need to find out what my JVM thinks a certain system property is set. For example, the installation instructions of some software packages would say something like "put this file in the lib subdirectory of what your JVM thinks is java.home."

What I would usually do is to write a throw away Java program that prints out the said property. And of course you get tired of doing this tedious chore after a while. That's when you write a little script to do the work.

Here's my little script. It's call jenv, and it is written in the BeanShell scripting language:

[weiqi@gao]$ cat jenv
#!/usr/bin/env bsh

// Get all the system properties
props = System.getProperties();

if (bsh.args.length == 0) {
  // print them all
  for (name : props.propertyNames()) {
    print(name + "=" + props.getProperty(name));
  }
} else {
  outer_for:
  for (name : props.propertyNames()) {
    for (regex : bsh.args) {
      if (name.matches(".*" + regex + ".*")) {
        print(name + "=" + props.getProperty(name));
        break outer_for;
      }
    }
  }
}

It can be run anywhere a bash shell is available (Cygwin on Windows or Linux.) When this script is run bash delegates to another shell script called bsh passing the path name of the script file and any arguments. On Linux, my bsh script contains only the line:

java bsh.Interpreter "$@"

In Cygwin, since the file name passed to bsh is in Cygwin format, which Java doesn't understand, my bsh script has to do a little bit more:

#!/bin/bash
#
# Run the BeanShell command line interpreter
#
declare -a args
declare -i index

until [ -z "$1" ]
do
  if echo $1 | egrep -q '^/|^\.'
  then
    args[index]=`cygpath -a -w $1`
  else
    args[index]=$1
  fi
  ((index++))
  shift
done

java bsh.Interpreter ${args[@]}

The weird looking loop is there to straighten out any Cygwin path names to the Windows format so that Java can understand them. It's stolen from another script I've written.

Now that I have the scripts, finding out the values of system properties is as easy as finding out the values of environment variables. The command jenv by itself print out all system properties. If any command line arguments are supplied, they are used as regular expressions to filter the system properties. Only system properties whose name contains a substring that matches one of the regular expressions are printed.

[weiqi@gao]$ jenv user.home
user.home=C:\Documents and Settings\gao_w
[weiqi@gao]$ jenv user home
user.country=US
user.dir=u:\bin
user.variant=
user.home=C:\Documents and Settings\gao_w
user.timezone=
user.name=gaow
java.home=C:\Program Files\Java\jre1.5.0_07
user.language=en

Weiqi Gao's Observations - beanshell tag

Kyle Cordes: Scripting Your Java App

Where Is My java.home?