This Servelet listener is to work around https://github.com/jruby/jruby/issues/788 Written by bbrowning.

gistfile1.java

// Add this as a listener in your web.xml file prior to loading jruby-rack.
//
//
//  <listener>
//		<listener-class>lib.JnrConstantHackListener</listener-class>
//	</listener>
//	<listener>
//	  <listener-class>org.jruby.rack.rails.RailsServletContextListener</listener-class>
//	</listener>

package lib;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import jnr.constants.ConstantSet;

public class JnrConstantHackListener implements ServletContextListener {

    public void contextInitialized(final ServletContextEvent event) {
        ConstantSet.getConstantSet( "AddressFamily" );
        ConstantSet.getConstantSet( "Errno" );
        ConstantSet.getConstantSet( "Fcntl" );
        ConstantSet.getConstantSet( "INAddr" );
        ConstantSet.getConstantSet( "IPProto" );
        ConstantSet.getConstantSet( "NameInfo" );
        ConstantSet.getConstantSet( "OpenFlags" );
        ConstantSet.getConstantSet( "PRIO" );
        ConstantSet.getConstantSet( "ProtocolFamily" );
        ConstantSet.getConstantSet( "RLIM" );
        ConstantSet.getConstantSet( "RLIMIT" );
        ConstantSet.getConstantSet( "Shutdown" );
        ConstantSet.getConstantSet( "Signal" );
        ConstantSet.getConstantSet( "Sock" );
        ConstantSet.getConstantSet( "SocketLevel" );
        ConstantSet.getConstantSet( "SocketOption" );
        ConstantSet.getConstantSet( "Sysconf" );
        ConstantSet.getConstantSet( "TCP" );
        ConstantSet.getConstantSet( "WaitFlags" );
    }

    public void contextDestroyed(final ServletContextEvent event) {
    }
}