写入工作簿WorkBook.write（out）Apache POI时获取java.lang.NullPointerException

Question

I am getting java.lang.NullPointerException while writing in to an output stream:

workbook.write(new FileOutputStream("test1.xslx"));

The exception is:

Exception:
   java.lang.NullPointerException
      at org.apache.poi.POIXMLDocument.write(POIXMLDocument.java:201)
      at ExcelCompare.WriteOutputIntoExcel.addRow(WriteExcel.java:124)
      at ExcelCompare.CompareExcel.main(MainClassExcelCompare.java:113)

Here I have two class: CompareExcel class and WriteOutputIntoExcel

I want to compare two excel sheets Excel1.xslx and Excel2.xslx and put result back in to Result.xslx .

I don't want put everything in Result.xslx , I just want to put the rows which don't match in both Excel1 and Excel2.

Here is the Main class

package ExcelCompare;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Iterator;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.IndexedColors;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class CompareExcel {

    public static void main(String[] args) {

        try {
            int temp;

            File excel1 = new File("C://Users/ckothakapax076037/Desktop/Demo1.xlsx");
            FileInputStream fis1 = new FileInputStream(excel1);
            XSSFWorkbook book1 = new XSSFWorkbook(fis1);
            XSSFSheet sheet1 = book1.getSheetAt(0);

            File excel2 = new File("C://Users/ckothakapax076037/Desktop/Demo2.xlsx");
            FileInputStream fis2 = new FileInputStream(excel2);
            XSSFWorkbook book2 = new XSSFWorkbook(fis2);
            XSSFSheet sheet2 = book2.getSheetAt(0);

            WriteExcel obj1 = new WriteExcel();
            obj1.setOutputFile("C://Users/ckothakapax076037/Desktop/Result.xlsx");

            //Get iterator to all the rows in current sheet
            Iterator<Row> itr1 = sheet1.iterator();
            Iterator<Row> itr2 = sheet2.iterator();

            // Iterating through all cells row by row
            while (itr1.hasNext() && itr2.hasNext()) {

                temp = 0;
                int j = 0;
                Row row1 = itr1.next();
                Row row2 = itr2.next();

                //Get iterator to all cells of current row
                Iterator<Cell> cellIterator1 = row1.cellIterator();
                Iterator<Cell> cellIterator2 = row2.cellIterator();

                CellStyle style = book1.createCellStyle();
                style = book1.createCellStyle();
                style.setFillForegroundColor(IndexedColors.RED.getIndex());
                style.setFillPattern(CellStyle.SOLID_FOREGROUND);

                while (cellIterator1.hasNext() && cellIterator2.hasNext()) {
                    Cell cell1 = cellIterator1.next();
                    Cell cell2 = cellIterator2.next();

                    switch (cell1.getCellType()) {
                        case Cell.CELL_TYPE_STRING:
                            System.out.print(cell1.getStringCellValue() + "\t");
                            System.out.print(cell2.getStringCellValue() + "\t");

                            if (!cell1.getStringCellValue().equalsIgnoreCase(cell2.getStringCellValue())) {
                                temp++;
                                cell1.setCellStyle(style);
                            }
                            break;
                        case Cell.CELL_TYPE_NUMERIC:
                            System.out.print(cell1.getNumericCellValue() + "\t");
                            System.out.print(cell2.getNumericCellValue() + "\t");

                            if (cell1.getNumericCellValue() != cell2.getNumericCellValue()) {
                                temp++;
                                cell1.setCellStyle(style);
                            }
                            break;
                        case Cell.CELL_TYPE_BOOLEAN:
                            System.out.print(cell1.getBooleanCellValue() + "\t");
                            System.out.print(cell2.getBooleanCellValue() + "\t");
                            break;
                        case Cell.CELL_TYPE_BLANK:
                            System.out.print(cell1.getNumericCellValue() + "\t");
                            System.out.print(cell2.getNumericCellValue() + "\t");

                            if (cell2.getStringCellValue() != " ") {
                                temp++;
                                cell1.setCellStyle(style);
                            }
                            break;
                        default:
                    }
                    j++;
                }

                System.out.print("\n");
                System.out.print("Flag value:" + temp);
                System.out.print("\n");

                if (temp >= 1) {
                    obj1.addRow(row1.cellIterator(), row2.cellIterator());
                }
            }

            book1.close();
            fis1.close();
            book2.close();
            fis2.close();
            obj1.closerActivity();

        } catch (FileNotFoundException fe) {
            fe.printStackTrace();
        } catch (IOException ie) {
            ie.printStackTrace();
        } catch (Exception ee) {
            ee.printStackTrace();
        }
    }
}

And now I have WriteOutputIntoExcel class to put result back in to Result.xslx

package ExcelCompare;

import java.io.FileOutputStream;
import java.util.Iterator;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.CellStyle;
import org.apache.poi.ss.usermodel.IndexedColors;
import org.apache.poi.xssf.usermodel.XSSFRow;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class WriteOutputIntoExcel {

    private static String OutputFile;
    private static XSSFWorkbook myWorkBook = new XSSFWorkbook();
    private static XSSFSheet mySheet = myWorkBook.createSheet("Report");

    public static int i = 0;

    public void setOutputFile(String OutputFile1) {
        OutputFile = OutputFile1;
    }

    public void addRow(Iterator<Cell> cellIterator1, Iterator<Cell> cellIterator2) {

        try {
            XSSFRow row = mySheet.createRow(i++);
            CellStyle style = myWorkBook.createCellStyle();
            style = myWorkBook.createCellStyle();
            style.setFillForegroundColor(IndexedColors.RED.getIndex());
            style.setFillPattern(CellStyle.SOLID_FOREGROUND);

            FileOutputStream out = new FileOutputStream(OutputFile);

            System.out.print("Writing result from Sheet1");
            System.out.print("\n");

            while (cellIterator1.hasNext()) {

                int j = 0;
                Cell cell1 = cellIterator1.next();

                switch (cell1.getCellType()) {
                    case Cell.CELL_TYPE_STRING:
                        System.out.print(cell1.getStringCellValue() + "\t");
                        row.createCell(j).setCellValue(cell1.getStringCellValue());
                        row.createCell(j).setCellStyle(style);

                        break;
                    case Cell.CELL_TYPE_NUMERIC:
                        System.out.print(cell1.getNumericCellValue() + "\t");
                        row.createCell(j).setCellValue(cell1.getNumericCellValue());
                        row.createCell(j).setCellStyle(style);
                        break;
                    case Cell.CELL_TYPE_BLANK:
                        System.out.print(cell1.getStringCellValue() + "\t");
                        row.createCell(j).setCellValue(cell1.getStringCellValue());
                        row.createCell(j).setCellStyle(style);
                        break;
                    default:
                        System.out.print(cell1.getStringCellValue() + "\t");
                        row.createCell(j).setCellValue(cell1.getStringCellValue());
                        row.createCell(j).setCellStyle(style);
                }
                j++;
            }

            System.out.print("\n");
            System.out.print("Writing result from Sheet2");
            System.out.print("\n");

            while (cellIterator2.hasNext()) {
                int j = 0;
                Cell cell2 = cellIterator2.next();

                switch (cell2.getCellType()) {
                    case Cell.CELL_TYPE_STRING:
                        System.out.print(cell2.getStringCellValue() + "\t");
                        row.createCell(j).setCellValue(cell2.getStringCellValue());

                        break;
                    case Cell.CELL_TYPE_NUMERIC:
                        System.out.print(cell2.getNumericCellValue() + "\t");
                        row.createCell(j).setCellValue(cell2.getNumericCellValue());

                        break;
                    case Cell.CELL_TYPE_BLANK:
                        System.out.print(cell2.getStringCellValue() + "\t");
                        row.createCell(j).setCellValue(cell2.getStringCellValue());

                        break;
                    default:
                        System.out.print(cell2.getStringCellValue() + "\t");
                        row.createCell(j).setCellValue(cell2.getStringCellValue());
                }
                j++;
            }

            System.out.print("\n");
            myWorkBook.write(out);
            out.close();
            myWorkBook.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void closerActivity() {
        try {
            System.out.println(" Hi i am in close");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

I also want to highlight the cells in Excel1 which are not same as Excel2 .

Please help me to achieve this.

Answer 1

The best way to tackle this kind of problems is also attaching the sourcecode of your library (in this case POI) to your IDE, so you can quickly lookup what is happening at line 201 in the library. Please note that you need to be sure that your library lib version is the same as the src version, because else things you can look at the wrong line.

Ok, most likely one of your arguments to addRow is null (iterators). So first check that (println).