Wikk Wikk - 4 months ago 21
Java Question

Loading GAMS Java API in JRuby

I'm working on a Java/JRuby project which needs to be able to be able to interact with GAMS. I know we can use the Java API, but I would really like to be able to access it using JRuby if possible, since we're hoping to eventual add a DSL and some other complexity I'm not really excited about having to implement in pure Java.

Following the official Java API documentation for GAMS, I have downloaded and setup everything necessary to run GAMS from the command line, but I can't figure out how to include the GAMS directory in LD_LIBRARY_PATH and still run JRuby irb. When I run

export LD_LIBRARY_PATH=/home/wikk/Downloads/gams24.0_linux_x64_64_sfx

Then try to run irb with JRuby, I get

jruby: /home/wikk/Downloads/gams24.0_linux_x64_64_sfx/libstdc++.so.6: version 'GLIBCXX_3.4.15' not found (required by jruby)

I think this is what the documentation is asking me to do to run a Java program that calls the API, is there maybe some way to set LD_LIBRARY_PATH in irb, but before importing all the Java class files? I can do this successfully if I don't set LD_LIBRARY_PATH, but then GAMS tells me it can't find the main program when I try to create a new GAMSWorkspace object:

irb(main):002:0> ws = GAMSWorkspace.new
Java::ComGamsApi::GAMSException: could not find a GAMS system directory from
your environment variable, please set up properly before running a program!
from com.gams.api.GAMSWorkspace.verifySystemDirectory(GAMSWorkspace.java:335)

Am I doing this wrong? or does the API require some Java feature that isn't implemented in JRuby?


Finally came back to this problem, got it working through some trial and error. I also needed to run jruby with the -J-Djava.library.path=[GAMSDIR]/apifiles/Java/api flag, and add [GAMSDIR]/apifiles/Java/api/GAMSJavaAPI.jar to the classpath.

Once this is all in place, you can run gams models from ruby scripts:

    import com.gams.api.GAMSWorkspace
    import com.gams.api.GAMSJob
    import com.gams.api.GAMSVariable
    import com.gams.api.GAMSVariableRecord
    import com.gams.api.GAMSWorkspace

    ws = GAMSWorkspace.new

    j1 = ws.addJobFromGamsLib('trnsport')


    j1.out_db.get_variable('x').each_entry do |rec|
      puts "x(#{rec.get_keys[0]}, #{rec.get_keys[1]}): level = #{rec.get_level},   marginal = #{rec.get_marginal}"