在Java開發中，CSV與XLS轉換是常見的需求。CSV是指逗號分隔值文件，XLS則是指Microsoft Excel文件。本文將介紹如何使用Java實現CSV與XLS之間的轉換。

CSV轉換為XLS的過程很簡單，只需要利用Java提供的POI庫即可。以下是轉換的代碼：

File csvFile = new File("test.csv");
File xlsFile = new File("test.xls");
try (FileInputStream inputStream = new FileInputStream(csvFile)) {
HSSFWorkbook workbook = new HSSFWorkbook();
HSSFSheet sheet = workbook.createSheet("Sheet1");
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
int rowNumber = 0;
while ((line = reader.readLine()) != null) {
String[] fields = line.split(",");
HSSFRow row = sheet.createRow(rowNumber++);
for (int i = 0; i< fields.length; i++) {
HSSFCell cell = row.createCell(i);
cell.setCellValue(fields[i]);
}
}
FileOutputStream outputStream = new FileOutputStream(xlsFile);
workbook.write(outputStream);
} catch (IOException e) {
e.printStackTrace();
}

以上代碼將把test.csv導出為test.xls文件。

反過來，將XLS轉換為CSV則需要借助第三方庫。下面以使用JExcelAPI為例：

File xlsFile = new File("test.xls");
File csvFile = new File("test.csv");
try (InputStream inputStream = new FileInputStream(xlsFile)) {
Workbook workbook = Workbook.getWorkbook(inputStream);
Sheet sheet = workbook.getSheet(0);
BufferedWriter writer = new BufferedWriter(new FileWriter(csvFile));
for (int row = 0; row< sheet.getRows(); row++) {
for (int col = 0; col< sheet.getColumns(); col++) {
writer.write(sheet.getCell(col, row).getContents());
if (col< sheet.getColumns() - 1) {
writer.write(",");
}
}
writer.newLine();
}
writer.flush();
writer.close();
} catch (Exception e) {
e.printStackTrace();
}

以上代碼將test.xls導出為test.csv文件。