Reading EXCEL file in Java using jxl

Question

I have a problem with reading xls files into Java usin jxl library.

Could you tell me what is wrong my code? I attached below. Something is wrong wif fillData method. The console returns:

Exception in thread "Thread-1" java.lang.NullPointerException
    at StudentLogin.fillData(StudentLogin.java:104)
    at StudentLogin.<init>(StudentLogin.java:70)
    at Login$PBar.run(Login.java:103)
    at java.base/java.lang.Thread.run(Unknown Source)

Thank you in advance for your help.

 public void fillData(File file) {
            Workbook workbook = null;
            try {
                workbook = Workbook.getWorkbook(file);
            }
            catch (Exception e) {
            }

            Sheet sheet = workbook.getSheet(0);

            headers.clear();
            for (int i = 0; i < sheet.getColumns(); i++) {
                Cell cell = sheet.getCell(i, 0);
                headers.add(cell.getContents());
            }

            data.clear();
            for (int j = 1; j < sheet.getRows(); j++) {
                Vector<String> d = new Vector<String>();
                for (int i = 0; i < sheet.getColumns(); i++) {
                    Cell cell = sheet.getCell(i, j);
                    d.add(cell.getContents());
                }
                d.add("\n");
                data.add(d);
            }
        }

Thiago Procaci · Answer 1 · 2018-06-09T21:31:18.937

I would recommend you to take a look at two parts of the method fillData:

1) try-catch probably hides the problem: in the beginning, you call the method getWorkbook which, according to its java doc, can throw an exception if, for instance, the file does not exist. However, you call the getWorkbook in a try-catch block which does not even print the exception. Consequently, if anything goes wrong you will get a null pointer at workbook.getSheet(0) cause the variable workbook keeps holding a null value (as you assign null in the first line of the method). To avoid this problem you can add a printStackTrace in the catch block. Another option is to add a throws Exception in the method definition and remove the try-catch block. Doing this, you may find the real cause of the null pointer.

 try {
      workbook = Workbook.getWorkbook(file);
 } catch (Exception e) {
      e.printStackTrace();
 }

OR

public void fillData(File file) throws Exception {

 Workbook workbook = Workbook.getWorkbook(file);
 ....
}

2) Is the variable headers globally initialized? I can't see in your code where you initialize the variable headers (doing like headers = new ArrayList()). If you did not do it, you will get a null pointer at headers.clear(). Moreover, the same problem can happen with the variable data if you don't initialize it.

Thank you. I used the second option and now I have following problem: Error:(88, 41) java: unreported exception java.lang.Exception; must be caught or declared to be thrown Error:(73, 25) java: unreported exception java.lang.Exception; must be caught or declared to be thrown I initalized a headers in the beginning of my class so it could work well. private Vector headers = new Vector(); — bwczech, Jun 10 '18 at 08:45
It seems to be a compiler error. For more information, see: https://stackoverflow.com/questions/908672/why-do-i-get-exception-must-be-caught-or-declared-to-be-thrown-when-i-try-to — Thiago Procaci, Jun 10 '18 at 20:37

Reading EXCEL file in Java using jxl

1 Answers1