useful swing border

This could be useful to have a graphical view of how much space a component is taking on the screen.

class JComponent
  def create_border
    setBorder(BorderFactory.createLineBorder(Color.black))
  end
end

jruby monkeypatching java methods

require "java"

a = java.util.ArrayList
a.instance_eval do
  alias :size_original :size

  def size
     puts "calling size method"
     size_original
  end
end

As simple as that, you could redefine methods in your Java code. It’s not always good practice to monkeypatch, as inheritance is as effective, but in case of one-off scripts, it could be the way to go.

start jirb from jruby jar

Run this:

java -jar jruby.jar -S jirb

nokogiri on jruby

Here’s what I did to be able to use nokogiri (1.4.1) on JRuby jruby 1.5.0.RC3:

1. jgem install nokogiri

2. add

   require "java"

   at the top of your script, before require “nokogiri”

3. overwrite the dll’s in nokogiri’s ext folder with ones from libxml, specifically libxslt-1.1.26.win32.zip and libxml2-2.7.6.win32.zip
4. run the script with:

   jruby -X+O

   to enable ObjectSpace.

Enjoy!

how to run your java class’s main method from jruby

Last night I wrote a Java class that performs a checkout from a SVN repository. I was able to integrate it with Groovy really fast, and was wondering how fast I could get it going with JRuby. I started to do some research on google, I downloaded the JRuby binary from http://dist.codehaus.org/jruby/, and I fired up jirb to do some quick testing.
Before I get to the JRuby part, let me add a little bit of information about the class I wanted to run: the only method I was interested to run was main, because most of the information was hardcoded in it.

So, I imported Java’s String class, hoping to build an array I could pass to main.

java_import "java.lang.String" do |package,classname|
   "J#{classname}"
end

This imports Java’s String class under the name JString, because Ruby has a String class as well. To create a JString object, you use Ruby’s regular object creation syntax :

JString.new("whatever")

Ok, so after I imported the java.lang.String class, I created an array of them:

args = [JString.new("argument"),JString.new("otherArgument")]

And I passed it to the class’s main method :

require "java"

java_import "java.lang.String" do |pk,nm|
  "J#{nm}"
end

java_import "SCli"
args = [JString.new("first_arg"),JString.new("second_arg")]
SCli.main(args)

Notice I imported the SCli class as well. That is my Java class. In order for the import to work, you should place the class in the CLASSPATH variable, or add the class file to your JRuby project’s lib folder and add that folder to the CLASSPATH. Also, if your class is inside a package, you should add that to the java_import line. Mine wasn’t in one.

Running this script gave me the following error :

main.rb:9: for method main expected [#<Java::JavaClass:0x9d5793>]; got: [org.jruby.RubyArray]; error: argument type mismatch (TypeError)

I was kind of hoping the array would pass for a Java array 🙂 . So, I started to search after this error message, and I got to the Calling Java from JRuby page. After a little bit of reading, I got it to work using the following script :

require "java"

java_import "SCli"
args = ["arg1","arg2"].to_java(:string)
SCli.main(args)

Nice,right?