Problems Calling a Java Class from JRuby

Question

I'm trying to use boilerpipe from JRuby. I've seen the guide for calling Java from JRuby, and have used it successfully with another Java package, but can't figure out why the same thing isn't working with boilerpipe.

I'm trying to basically do the equivalent of this Java from JRuby:

URL url = new URL("http://www.example.com/some-location/index.html");
String text = ArticleExtractor.INSTANCE.getText(url);

Tried this in JRuby:

require 'java'
url = java.net.URL.new("http://www.example.com/some-location/index.html")
text = Java::DeL3sBoilerpipeExtractors::ArticleExtractor.INSTANCE.getText(url)

This is based on the API Javadocs for boilerpipe. Here's the error:

jruby-1.6.0 :042 > Java::DeL3sBoilerpipeExtractors::ArticleExtractor
NameError: cannot load Java class deL3sBoilerpipeExtractors.ArticleExtractor
        from org/jruby/javasupport/JavaClass.java:1195:in `for_name'
        from org/jruby/javasupport/JavaUtilities.java:34:in `get_proxy_class'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/site_ruby/shared/builtin/javasupport/java.rb:45:in `const_missing'
        from (irb):42:in `evaluate'
        from org/jruby/RubyKernel.java:1087:in `eval'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:158:in `eval_input'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:271:in `signal_status'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:270:in `signal_status'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:155:in `eval_input'
        from org/jruby/RubyKernel.java:1417:in `loop'
        from org/jruby/RubyKernel.java:1190:in `catch'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:154:in `eval_input'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:71:in `start'
        from org/jruby/RubyKernel.java:1190:in `catch'
        from /usr/local/rvm/rubies/jruby-1.6.0/lib/ruby/1.8/irb.rb:70:in `start'
        from /usr/local/rvm/rubies/jruby-1.6.0/bin/irb:17:in `(root)'

Looks like it didn't parse the camelcase into the appropriate Java package name. What am I doing wrong? I believe I've set up my classpath alright (last 3 entries), though there may be some conflict with xerces possibly being included twice:

$ echo $CLASSPATH
:/jellly/Maui1.2:/jellly/Maui1.2/src:/jellly/Maui1.2/bin:/jellly/Maui1.2/lib/commons-io-1.4.jar:/jellly/Maui1.2/lib/commons-logging.jar:/jellly/Maui1.2/lib/icu4j_3_4.jar:/jellly/Maui1.2/lib/iri.jar:/jellly/Maui1.2/lib/jena.jar:/jellly/Maui1.2/lib/maxent-2.4.0.jar:/jellly/Maui1.2/lib/mysql-connector-java-3.1.13-bin.jar:/jellly/Maui1.2/lib/opennlp-tools-1.3.0.jar:/jellly/Maui1.2/lib/snowball.jar:/jellly/Maui1.2/lib/trove.jar:/jellly/Maui1.2/lib/weka.jar:/jellly/Maui1.2/lib/wikipediaminer1.1.jar:/jellly/Maui1.2/lib/xercesImpl.jar:/jellly/boilerpipe-1.1.0/boilerpipe-1.1.0.jar:/jellly/boilerpipe-1.1.0/lib/nekohtml-1.9.13.jar:/jellly/boilerpipe-1.1.0/lib/xerces-2.9.1.jar

Charles Oliver Nutter · Accepted Answer · 2011-03-22 19:18:33Z

11

I'd recommend against trying to guess the module name we put under Java::, since for unusual packages it can get mangled pretty badly. Use java_import 'your.weird.package.ArticleExtractor' or if all the package components are compatible with Ruby method naming, you can also do Java::your.weird.package.ArticleExtractor.

Also, since you might run into this... you'll want to reference the INSTANCE variable as ArticleExtractor::INSTANCE, since we map it as a Ruby constant.

Have fun!

answered Mar 22, 2011 at 19:18

Charles Oliver Nutter

1,52510 silver badges5 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Christian Kohlschütter Over a year ago

Apologies for creating packages starting with "de.l3s". L3S is the name of the company/research center I was working for when developing the boilerpipe library http://www.L3S.de/

Jörg W Mittag Over a year ago

You gotta love StackOverflow. Ask a question about using a library from JRuby and you get the lead developer of JRuby and the creator of the library answering! (Within 6 minutes of asking the question, no less.)

Charles Oliver Nutter Over a year ago

I only answer the easy ones that quickly :)

Gregory Ostermayr · Accepted Answer · 2017-09-08 20:50:05Z

0

You can also use the nice Jruby Boilerpipe Gem which wraps the Java code

Or the pure ruby implementation of Boilerpipe Ruby Boilerpipe Gem

require 'boilerpipe'  

Boilerpipe::Extractors::ArticleExtractor.text("https://github.com/jruby/jruby/wiki/AboutJRuby")

answered Sep 8, 2017 at 20:50

Gregory Ostermayr

1,12110 silver badges18 bronze badges

Collectives™ on Stack Overflow

Problems Calling a Java Class from JRuby

2 Answers 2

3 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related