Apache POI获取NPE读取xls文件

Question

I'm trying to read an XLS file into java, which looks something like this

Column A|Product ID|Number Sold
.................|105029 ....|15
.................|102930 ....|9
.................|203911 ....|29
.................|105029 ....|4

where I need to add up the total number of product sold for each product ID and then create a new file with the data sorted. This program is supposed to be flexible, as in there could be 1000 different product ID's or 400. The code below is what I have so far... but there are quite a few problems with it and my lack of java knowledge is making it really frustrating.

The first for loop does not continue, it's stuck at r=1, although the second for loop continues.

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;

public class Read {

            public static void readXLSFile() throws IOException{
           InputStream ExcelFile = new FileInputStream("C:/Sales Data.xls");
                HSSFWorkbook wb = new HSSFWorkbook(ExcelFile);
                HSSFSheet sheet=wb.getSheetAt(0);

                int numRows = sheet.getPhysicalNumberOfRows(); 
                //to intialize an array
                int[]idAccum = new int[numRows]; 
                //holds the product id
                int[]saleAccum = new int[numRows]; 
                //holds the total sales per product ID

                        for(int r=1;r<=numRows;r++){ 
                        //iterates through the product ID and matching sales
                            for(int j=r+1;j<numRows+1; j++){
                            HSSFCell rows = sheet.getRow(r).getCell(1);
                            HSSFCell cells = sheet.getRow(r).getCell(2);
                            HSSFCell rows1 = sheet.getRow(j).getCell(1);
                            HSSFCell cells1 = sheet.getRow(j).getCell(2);
                                if(rows==rows1){ 
                            //compares product ids
                                    idAccum[r]=rows1.getNumericCellValue(); 
                        //places product id in element r if rows and rows1 match
                                    saleAccum[r]+=cells.getNumericCellValue(); 
                        //adds number of items sold to corresponding product ID
                                }
                            }
                            System.out.println(idAccum[r]); 
                            System.out.println(saleAccum[r]);
                        }   
            }

            public static void main(String[] args) throws IOException {
        readXLSFile();

            }
}

But I'm getting nullpointexceptions.

Exception in thread "main" java.lang.NullPointerException
at Read.readXLSFile(Read.java:29)
at Read.main(Read.java:45)
Java Result: 1

Answer 1

You have an off-by-one error: r goes up to numRows , and j starts out at r + 1 – which during the last iteration is numRows + 1 . Since there is no content in that row, getCell(…) on it will return null (as per the API definition). This is where the NullPointerException is coming from.

Change

for(int r=1;r<=numRows;r++){

to

for(int r=1;r<numRows;r++){

to get rid of the error. Also defensive programming (ie checking getCell(…) results for null is a good idea.