java.lang.NoClassDefFoundError: org/apache/log4j/Logger error [duplicate]

So I got a request converting xls to xlsx. After a few hours of researching all sites and solutions I managed to adapt some code i found on various site... Now I am stuck with a java.lang.NoClassDefFoundError: org/apache/log4j/Logger

here is a list all my libs i am using to get this working so far, I had to add a few libs just to get this far and now i am stuck.

dropbox-core-sdk-1.7.7, itextpdf-5.3.0, jackson-core-2.2.4, PDFBox-0.7.3, poi-3.10-FINAL-20140208, poi-ooxml-3.5-beta5, poi-ooxml-schemas-3.10-beta1, rs2xml, slf4j-api-1.7.5, sqlite, sqlite-jdbc-3.8.7, xmlbeans 

Below is my code where i call he class

private void exportRepBtnActionPerformed(java.awt.event.ActionEvent evt) { connect(); exportRepairReport(); // This is where I am trying to convert the xls file convertExcelFiles.convertWorkbookHSSFToXSSF(workbook); // int selectedOption = JOptionPane.showConfirmDialog(null, "Generate Comprehensive Report?", "OPTIONAL", JOptionPane.YES_NO_OPTION); if (selectedOption == JOptionPane.YES_OPTION) { exportRawRepairs(); } } 

Hers is the class where things go south.

public static XSSFWorkbook convertWorkbookHSSFToXSSF(HSSFWorkbook source) { XSSFWorkbook retVal = new XSSFWorkbook(); for (int i = 0; i < source.getNumberOfSheets(); i++) { XSSFSheet xssfSheet = retVal.createSheet(); HSSFSheet hssfsheet = source.getSheetAt(i); copySheets(hssfsheet, xssfSheet); } return retVal; } 

Any help will be appreciated, let me know if you need more info.

Thanks in advance.