Re: [Jpype-users] Problem with JPype (newbie)

[Tobias I. <th...@gm...>]

I don't know if you have received any response from anyone else. I have had
this email in my todo-queue for a few days now, and had some time to reply
to it today.

It sounds to me as if you are having classpath issues (the most disturbing
problem in the java-world in my opinion).
How do you ensure that the package containing your class-files are reachable
by the JVM? I have found that the best way is to put the jar in the java
extension directory. I believe it is located at $JAVA_HOME\lib\ext on
windows.
Try to put weka.jar there, that worked for me in a similar case.


I really think that the JPype startJVM method would be better if it had a
name-only parameter called classpath for specifying the
classpath, since this is something one would quite often do, and the current
way of specifying the classpath is quite awkward.

/Tobias

On 6/13/07, lc...@cs... <lc...@cs...> wrote:
>
> Hi,
>
> I am a newbie in python and JPype.  I need to use JPype to communicate
> a python program with the java program.  I tested a small java program
> that didn't have any external jar file (it just uses java.lang
> library) and I called it from a python program using JPype and It
> works fine.  I am using version JPype-0.5.2.1, wich is the latest that
> I found for python 2.4 (running on windows).  I am trying to run a
> program that uses the datamining library, weka, that is written in
> java (it is in a jar file: weka.jar which is in defined in the
> classpath, and when I run the java program independently it works
> fine).  My problem is that I get the following error message when I
> try to call the program from python using JPype:
>
> D:\Lorena\weka\examples>python Nav1.py
> Traceback (most recent call last):
>    File "Nav1.py", line 7, in ?
>      csvArffClass.convert("bank-data.csv","bank-data.arff")
> jpype._jexception.java.lang.LinkageErrorPyRaisable:
> java.lang.NoClassDefFoundErr
> or: weka/core/converters/CSVLoader
>
> Here is the code:
>
> Nav1.py
> ------------
>
> from jpype import *
>
> startJVM("c:/Program Files/Java/jdk1.6.0_01/jre/bin/server/jvm.dll",
> "-ea")
> csvArffClass = JClass("CSV2Arff")
> csvArffClass.convert("bank-data.csv","bank-data.arff")
> shutdownJVM()
>
> CSV2Arff.java
> --------------------
>
> import weka.core.Instances;
> import weka.core.converters.ArffSaver;
> import weka.core.converters.CSVLoader;
>
> import java.io.File;
>
> public class CSV2Arff {
>
>    public static void convert(String inputfile, String outputfile)
>    {
>      try
>      {
>         // load CSV
>         CSVLoader loader = new CSVLoader();
>         loader.setSource(new File(inputfile));
>         Instances data = loader.getDataSet();
>
>         // save ARFF
>         ArffSaver saver = new ArffSaver();
>         saver.setInstances(data);
>         saver.setFile(new File(outputfile));
>         saver.setDestination(new File(outputfile));
>         saver.writeBatch();
>       }
>       catch (Exception e) {}
>    }
> }
>
>
> Please let me know what am I doing wrong?.
>
> Thanks,
>
> Lorena Carlo
>
>
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