Find cells by their column name and change data type - apache-poi

Question

I've a simple method to read csv and convert it to Excel:
public static void main(String[] args) throws Exception {
CSVReader csvReader = new CSVReader(new FileReader("P:\\employees.csv"));
SXSSFWorkbook sxssfWorkbook = new SXSSFWorkbook();
SXSSFSheet sxssfSheet = sxssfWorkbook.createSheet("Sheet");
String[] dataRow = null;
int rowNum = 0;
while ((dataRow = csvReader.readNext()) != null) {
Row currentRow = sxssfSheet.createRow(rowNum);
for (int i = 0; i < dataRow.length; i++) {
String cellValue = dataRow[i];
currentRow.createCell(i).setCellValue(cellValue);
}
rowNum++;
}
sxssfWorkbook.write(new FileOutputStream("P:\\employees.xlsx"));
}
But there's a problem with cell data type. All my data now represents as text. I want to find columns by their name (for example age, paid_total), not by index, and set numeric (float) data type for these columns. Something like this (sorry for sql-like style, for me it's a simplier to describe): WHEN columnName IN ('age', 'paid_total') SET allColumnType AS NUMERIC. How can I do this? Or it's only possible with indexes?

Answer 1

CSV files always are plain text files without data types. But if you exactly know which column should be which data type, then a type safe Excel sheet can be created. This can be achieved by column indes as well as by column header. To detect types by column header, those headers wolud must be into a separate data structure. But this will always be benefical.
Let's take the example employees.csv from here: https://gist.github.com/kevin336/acbb2271e66c10a5b73aacf82ca82784.
Then following should work:
import java.io.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;
import org.apache.poi.xssf.streaming.*;
import org.apache.poi.ss.SpreadsheetVersion;
import org.apache.poi.ss.util.AreaReference;
import org.apache.poi.ss.util.CellReference;
import com.opencsv.CSVReader;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.DateTimeFormatter;
import java.time.LocalDate;
class CreateExcelFromCSVDifferentDataTypes {
public static void main(String[] args) throws Exception {
try (
SXSSFWorkbook sxssfWorkbook = new SXSSFWorkbook(); FileOutputStream fileout = new FileOutputStream("./employees.xlsx");
CSVReader csvReader = new CSVReader(new FileReader("./employees.csv"));
) {
sxssfWorkbook.setCompressTempFiles(true);
CellStyle dateStyle = sxssfWorkbook.createCellStyle();
dateStyle.setDataFormat(sxssfWorkbook.getCreationHelper().createDataFormat().getFormat("dd-MMM-yy"));
SXSSFSheet sxssfSheet = sxssfWorkbook.createSheet("Sheet");
sxssfSheet.setRandomAccessWindowSize(100);
String[] strHeaders = null;
String[] dataRow = null;
int rowNum = 0;
while ((dataRow = csvReader.readNext()) != null) {
if (rowNum == 0) strHeaders = dataRow;
Row currentRow = sxssfSheet.createRow(rowNum);
for (int i = 0; i < dataRow.length; i++) {
String cellValue = dataRow[i];
if (rowNum > 0 && "HIRE_DATE".equals(strHeaders[i])) {
DateTimeFormatter formatter= new DateTimeFormatterBuilder().parseCaseInsensitive().appendPattern("dd-MMM-yy").toFormatter(java.util.Locale.ENGLISH);
LocalDate localDate = LocalDate.parse(cellValue, formatter);
currentRow.createCell(i).setCellValue(localDate);
currentRow.getCell(i).setCellStyle(dateStyle);
} else if (rowNum > 0 && "SALARY".equals(strHeaders[i])) {
double d = Double.valueOf(cellValue);
currentRow.createCell(i).setCellValue(d);
} else {
currentRow.createCell(i).setCellValue(cellValue);
}
}
rowNum++;
}
sxssfWorkbook.write(fileout);
sxssfWorkbook.dispose();
}
}
}