JTable导出到Excel文件时避免NullPointerException

Question

I have a JTable with no values (empty columns data). Like this,

|column 1|column 2|column 3|column 4|
-------------------------------------
|Java    |C#      |        |Ruby    |
-------------------------------------
|Java    |        |PHP     |Ruby    |

I am trying to export this JTable to an Excel File. When I press the button to export this it gives NullPointerException . Because of that null values. So I need to ignore it and continue exporting Excel Files.

Here is the code I used,

        XSSFWorkbook xb = new XSSFWorkbook();
        XSSFSheet xs = xb.createSheet();

        //Load data to TreeMap
        TreeMap<String,Object[]> data = new TreeMap<>();

        //Add Rows and Cells
        data.put("-1", new Object[]{pageTable.getColumnName(0), pageTable.getColumnName(1), pageTable.getColumnName(2), pageTable.getColumnName(3), pageTable.getColumnName(4), pageTable.getColumnName(5), pageTable.getColumnName(6)});

        for(int i = 0; i<pageTable.getRowCount(); i++)
        {
            data.put(Integer.toString(i), new Object[]{getCellValue(i, 0), getCellValue(i, 1), getCellValue(i, 2), getCellValue(i, 3), getCellValue(i, 4), getCellValue(i, 5), getCellValue(i, 6)});
        }

        //Write data to Excel
        Set<String> ids = data.keySet();
        XSSFRow row;
        int rowID = 0;

        for(String key: ids)
        {
            row = xs.createRow(rowID++);

            //Get data as per Key
            Object[] values = data.get(key);

            int cellID = 0;
            for(Object o: values)
            {
                Cell cell = row.createCell(cellID++);
                cell.setCellValue(o.toString());
            }
        }

And getCellValue Method;

private String getCellValue(int x, int y)
{
    return pageTable.getValueAt(x, y).toString();
}

And it gives this row is the cause,

data.put(Integer.toString(i), new Object[]{getCellValue(i, 0), getCellValue(i, 1), getCellValue(i, 2), getCellValue(i, 3), getCellValue(i, 4), getCellValue(i, 5), getCellValue(i, 6)});

So How can I fix it? Any way to avoid this?

Thanks for the help in advance! Best Regards.

Answer 1

As you are saying that some values can be null, so in this for loop,

for(Object o: values)
{
    Cell cell = row.createCell(cellID++);
    cell.setCellValue(o.toString());
}

o.toString() must be causing NullPointerException.

Just change second line in for loop from,

cell.setCellValue(o.toString());

to

cell.setCellValue(o==null?"":o.toString());

And this should avoid NPException and your code should work fine.

Let me know if this works fine else will help you further.

Edit 1:

Just read again and saw you suspecting your NPE in this method.

private String getCellValue(int x, int y)
{
    return pageTable.getValueAt(x, y).toString();
}

If this return statement is causing this, then don't call toString method without checking null value from getValueAt and change your method to this,

private String getCellValue(int x, int y)
{
    if( pageTable.getValueAt(x, y) == null) {
        return "";
    } else {
        pageTable.getValueAt(x, y).toString();
    }
}