Exception in thread "main" java.lang.NoClassDefFoundError: org/dom4j/DocumentException

[Alessandro9]

Buongiorno a tutti,
ho questo programma, ma quando lo eseguo mi da l'errore in oggetto

import java.io.FileOutputStream;
import java.io.IOException;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class SimpleExcelWriterExample {


    public static void main(String[] args) throws IOException {
        XSSFWorkbook workbook = new XSSFWorkbook();
        XSSFSheet sheet = workbook.createSheet("Java Books");

        Object[][] bookData = {
                {"Head First Java", "Kathy Serria", 79},
                {"Effective Java", "Joshua Bloch", 36},
                {"Clean Code", "Robert martin", 42},
                {"Thinking in Java", "Bruce Eckel", 35},
        };
int rowCount = 0;

for (Object[] aBook : bookData) {
            Row row = sheet.createRow(++rowCount);

            int columnCount = 0;

            for (Object field : aBook) {
                Cell cell = row.createCell(++columnCount);
                if (field instanceof String) {
                    cell.setCellValue((String) field);
                } else if (field instanceof Integer) {
                    cell.setCellValue((Integer) field);
                }
            }
}

        try (FileOutputStream outputStream = new FileOutputStream("JavaBooks.xlsx")) {
            workbook.write(outputStream);
        }
    }
}

ho aggiunto la libreria che mi chiede tra le librerie, appunto. Il risultato non cambia. Sapete aiutarmi? Cosa posso fare?