Question

i am a barely new to the java (was always on c# before) and need to create a swing application where i need to read a data from xls file. So i use jXL.

I have a class, which returns name of a first sheet from excel file, choosen in jFileChooser. Here is the code:

import java.io.File;
import jxl.Sheet;
import jxl.Workbook;

public class ExcelObject
{
    private String filename = null;
    private Workbook wb = null;
    private Sheet sheet = null;

    public ExcelObject(String f) 
    {
        filename = f;
    }

    public String getSheetName()
    {
        String sheet_name = null;

        try
        {
            wb = Workbook.getWorkbook(new File(filename));
            sheet = wb.getSheet(0);
            sheet_name = sheet.getName();
        }
        catch (Exception e) 
        {
            e.printStackTrace();
        }
        finally
        {
            wb.close();
        }

        return sheet_name;
    }

}   

in the program call looks like :

ExcelObject ex = new ExcelObject(filename);
String s = ex.getSheetName();
lblReport.setText(s);

So the issue is : when ran in the eclipse (3.4.2) i am getting a correct value, when jar is compiled, NO VALUE IS RETURNED! I mean lblReport is empty, with no exceptions and warnings.

Keep in mind : all other external jars work fine.

I tried a lot of things but none is working.

Also, if i do something like

                            ExcelObject ex = new ExcelObject(filename);
                            String s = ex.getSheetName();
//                          lblReportRun.setText(s);

                            lblReportRun.setText("Test");
                            lblAnyOtherLabel.setText("Test");

no text is displayed in the labels either, in compiled jar, and fine in eclipse.

Answer 1

This is probably because if some exception occurs when opening the workbook, you catch it, print the stack trace, and then close the workbook in the finally block. But since an exception occurred when calling Workbook.getWorkbook, the wb variable is still null, and you’re trying to invoke close on it. So a NullPointerException happens while in the finally block.

Watch your console, you must have some exception popping up.

Also, note that fileName should be the only instance variable of your class, that Java variable normally don’t contain underscores and use camelCase, and thet the fileName variable should be of type File, rather than String : you get a File from the file chooser, transform it into a string, and then transform it back to a File.

Another possibility, since it works in Eclipse and not when run externally, is that you forgot to put the jXL jar in the classpath, which causes some ClassNotFoundException when trying to use the ExcelObject class.