JRuby Embed (Red Bridge) Gotchas: __FILE__

About a month ago, I wrote __FILE__ didn't work when Ruby code was loaded from classpath in the thread, Load path issues inside jar / external app. Tracking jruby down with a debugger, I found out one solution. It was a combination of setting a feasible current directory and using File.expand_path.

Here's a test code:

# file_check.rb [Birch]

puts "__FILE__: #{__FILE__}"
puts "dirname: #{File.dirname(__FILE__)}"
puts "expanded path: #{File.expand_path(File.dirname(__FILE__))}"
puts "joined path 1: #{File.join(File.dirname(__FILE__), "abc.rb")}"
puts "joined path 2: #{File.join(File.expand_path(File.dirname(__FILE__)), "abc.rb")}"

// FileCheck.java
package vanilla;

import org.jruby.embed.LocalContextScope;
import org.jruby.embed.PathType;
import org.jruby.embed.ScriptingContainer;

public class FileCheck {

    private FileCheck() {
        //String userDir = System.getProperty("user.dir");
        //System.setProperty("user.dir", userDir+"/src/ruby");
        ScriptingContainer container = new ScriptingContainer(LocalContextScope.SINGLETHREAD);
        System.out.println("currentDirectory: " + container.getProvider().getRubyInstanceConfig().getCurrentDirectory());
        container.getProvider().getRubyInstanceConfig().setCurrentDirectory(System.getProperty("user.dir")+"/src/ruby");
        System.out.println("currentDirectory: " + container.getProvider().getRubyInstanceConfig().getCurrentDirectory());
        container.runScriptlet(PathType.CLASSPATH, "file_check.rb");
    }

    public static void main(String[] args) {
        new FileCheck();
    }
}

The absolute path to file_check.rb was /Users/yoko/NetBeansProjects/Birch/src/ruby/file_check.rb. So, I added the path, /Users/yoko/NetBeansProjects/Birch/src/ruby, to "-cp" option of java command. In a Java code, I set /Users/yoko/NetBeansProjects/Birch/src/ruby as the current directory. Then, the result was below:

yoko$ java -cp build/classes:/Users/yoko/DevSpace/jruby~main/lib/jruby.jar:./src/ruby  vanilla.FileCheck
currentDirectory: /Users/yoko/NetBeansProjects/Birch
currentDirectory: /Users/yoko/NetBeansProjects/Birch/src/ruby
__FILE__: file_check.rb
dirname: .
expanded path: /Users/yoko/NetBeansProjects/Birch/src/ruby
joined path 1: ./abc.rb
joined path 2: /Users/yoko/NetBeansProjects/Birch/src/ruby/abc.rb

As you see, a wrapped path by File.expand_path is correct though just File.dirname didn't work. The combination of setting the current directory and using File.expand_path would be the solution of this kind of cases. If you are using JSR223 or BSF, setting user.dir system property works as I commented out in the Java code. This is because JRuby uses the current directory when it expands a path, and the current directory is based on user.dir system property. If it is a web application, perhaps, we can set the current directory using ServletContext#getRealPath().