Appending data below the existing data in csv file Java

Question

I have a csv file which contains 14 columns and 5 rows. I'm reading contents of last column and I'm performing some mathematical operation on the column values and saving that in an array named exposureFactor[]. Now I have to write that array column wise below the first column skiping a row which is getting done perfectly. But when I run the program again it gives me this error.

Exception in thread "main" java.lang.NumberFormatException: For input string: ""
at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:68)
at java.base/java.lang.Integer.parseInt(Integer.java:662)
at java.base/java.lang.Integer.parseInt(Integer.java:770)
at java.base/java.util.stream.ReferencePipeline$4$1.accept(ReferencePipeline.java:212)
at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:550)
at java.base/java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:260)
at java.base/java.util.stream.IntPipeline.toArray(IntPipeline.java:538)
at com.sajood.Readingcsv.appendCol.main(appendCol.java:28)

Can someone please highlight the issue. It's a project given to me and it's deadline is in 2 days.

import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import au.com.bytecode.opencsv.CSVReader;

public class appendCol {

public static void main(String[] args) throws IOException {
    int sum = 0;
    String[] data5;
    CSVReader reader5 = new CSVReader(new FileReader("D:\\new.csv"));
    String[] nextLine5;
    List<String> li = new ArrayList<String>();
    while (null != (nextLine5 = reader5.readNext())) {
        li.add(nextLine5[nextLine5.length - 1]);

    }
    String[] tempe = li.toArray(new String[0]);
    String[] exp = Arrays.copyOfRange(tempe, 1, tempe.length);
    data5 = Arrays.toString(exp).replace("[", "").replace("]", "").replace("\"", "").replace(" ", "").split(",");
    int[] weightage = Arrays.stream(data5).mapToInt(Integer::parseInt).toArray(); 
    for (int i = 0; i < weightage.length; i++) {
        sum += weightage[i];
    }
    int average = sum / 6;
    String averageStr = String.valueOf(average);
    String exposureFactor[] = { "Exposure Factor", averageStr };
    FileWriter writer4 = new FileWriter("D:\\new.csv", true);
    CSVReader reader3 = new CSVReader(new FileReader("D:\\new.csv"), '\t', '\'', 6);
    if ((reader3.readNext()) != null) {
        return;
     } else {
        for (int j = 0; j < exposureFactor.length; j++) {
            if (j == 0) {
                writer4.append("\n");
            }
            writer4.append(String.valueOf(exposureFactor[j]));
            writer4.append("\n");
        }
        writer4.close();
    }
}

}

Answer 1

The only line it could be is:
int[] weightage = Arrays.stream(data5).mapToInt(Integer::parseInt).toArray();

I assume it's trying to parse your blank line as numbers. Why do you need to run it again after you've output your exposure factor?

---

If your boss reeeeeeeally needs to run it twice in a row, the quick fix is to add a try catch and make it exit "gracefully."

try {
    int[] weightage = Arrays.stream(data5).mapToInt(Integer::parseInt).toArray();
} catch (NumberFormatException e) {
    System.out.println("Program has already been run.");
    System.exit(0);
}

You could also use that if ((reader3.readNext()) != null) check if you feel like reworking things.

---

One more thing: you might want average to be a double instead of an int.