使用HSSF写入Excel时触发IndexOutOfBoundsException问题求助

Hey there! Let's figure out why you're running into that IndexOutOfBoundsException when writing your two String ArrayLists to Excel using HSSF. This is a super common pitfall, so let's break down the likely causes and how to fix them.

Common Causes & Solutions #

1. Trying to Access Rows/Cells That Don't Exist #

HSSF won't automatically create rows or cells for you. If you call sheet.getRow(rowIndex) on a row that hasn't been created yet, it returns null. Trying to create a cell on a null row will lead to errors, and even if that doesn't crash you, subsequent index operations can go haywire.

2. Mismatched ArrayList Sizes + Unchecked Index Access #

If your two ArrayLists have different lengths, looping based on one list's size and trying to access the other list at the same index will trigger an out-of-bounds error once you exceed the shorter list's length.

Correct Implementation Example #

Here's a robust way to write your ArrayLists to Excel without hitting exceptions:

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFRow;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;

public class ExcelWriter {
    public static void main(String[] args) {
        HSSFWorkbook workbook = new HSSFWorkbook();
        HSSFSheet sheet = workbook.createSheet("Data");

        // Your sample ArrayLists (could be different lengths)
        ArrayList<String> list1 = new ArrayList<>(Arrays.asList("Apple", "Banana", "Cherry"));
        ArrayList<String> list2 = new ArrayList<>(Arrays.asList("Red", "Yellow"));

        // Loop up to the longest list's size to cover all elements
        int maxRowCount = Math.max(list1.size(), list2.size());

        for (int rowIndex = 0; rowIndex < maxRowCount; rowIndex++) {
            // Create row if it doesn't exist yet
            HSSFRow row = sheet.getRow(rowIndex);
            if (row == null) {
                row = sheet.createRow(rowIndex);
            }

            // Write to first column only if index is within list1's bounds
            if (rowIndex < list1.size()) {
                row.createCell(0).setCellValue(list1.get(rowIndex));
            } else {
                // Optional: Fill empty cells with blank or skip creating the cell
                row.createCell(0).setCellValue("");
            }

            // Write to second column only if index is within list2's bounds
            if (rowIndex < list2.size()) {
                row.createCell(1).setCellValue(list2.get(rowIndex));
            } else {
                row.createCell(1).setCellValue("");
            }
        }

        // Write the workbook to file
        try (FileOutputStream outputStream = new FileOutputStream("output.xls")) {
            workbook.write(outputStream);
            workbook.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Key Fixes Explained #

• Always check for null rows: Before creating cells, ensure the row exists with sheet.createRow(rowIndex) if sheet.getRow(rowIndex) returns null.
• Handle mismatched list sizes: Use Math.max() to get the longest list's length as your loop boundary. Then, check if the current index is within each list's bounds before accessing elements.
• Optional empty cell handling: If one list is shorter, you can either fill the missing cells with blanks or skip creating them entirely—adjust based on your needs.

Debugging Tip #

If you're still stuck, add print statements inside your loop to track the current index and list sizes:

System.out.println("Row index: " + rowIndex + " | List1 size: " + list1.size() + " | List2 size: " + list2.size());

This will help you see exactly when the index exceeds a list's length.

内容的提问来源于stack exchange，提问作者xXJohnRamboXx