[Php-java-bridge-users] How to debug NoClassDefFoundError exceptions?

[<php...@li...>]

Hello,

I've got this error I'd like some help with. I'm using Apache POI 3.5
to read XLS and XLSX files, but trying to do:

$workbook = new org_apache_poi_xssf_usermodel_XSSFWorkbook();

fails with:

java.lang.Exception: CreateInstance failed: new
org.apache.poi.xssf.usermodel.XSSFWorkbook. Cause:
java.lang.ClassNotFoundException: Unresolved external reference:
java.lang.NoClassDefFoundError: Could not initialize class
org.openxmlformats.schemas.spreadsheetml.x2006.main.CTWorkbook. --
Unable to call constructor, see the README section "Java platform
issues" for details.

However, in the same page, when I call:

$wb = new org_openxmlformats_schemas_spreadsheetml_x2006_main_CTWorkbook();

the code doesn't complain. Also, a pure Java application that
instantiates XSSFWorkbook and manipulates it works fine.

So my question is: how to debug such problems? Where to start? I
downloaded DependencyFinder (http://depfind.sourceforge.net/) to see
if the referenced jars use other packages that are not present, but I
didn't find any.

TIA,
Karim