我需要将行附加到工作簿的工作表中。我正在使用 org.apache.poi.xssf.streaming.SXSSFWorkbook 但我无法实现低内存占用。以下是代码:
import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.xssf.streaming.SXSSFWorkbook;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;
public class ExcelHelper {
public static void createExcelFileWithLowMemFootprint(
ArrayList<HashMap<String, Object>> data,
ArrayList<String> fieldNames, String fileName, int rowNum) {
try {
if (rowNum == 0) {
// Creating a new workbook and writing the top heading here
SXSSFWorkbook workbook = new SXSSFWorkbook(1000);
Sheet worksheet = workbook.createSheet("Sheet 1");
int i = 0;
Iterator<String> it0 = fieldNames.iterator();
Row row = worksheet.createRow(i);
int j = 0;
while (it0.hasNext()) {
Cell cell = row.createCell(j);
String fieldName = it0.next();
cell.setCellValue(fieldName);
j++;
}
rowNum++;
FileOutputStream fileOut = new FileOutputStream(fileName);
workbook.write(fileOut);
fileOut.flush();
fileOut.close();
}
InputStream fileIn = new BufferedInputStream(new FileInputStream(
fileName), 1000);
SXSSFWorkbook workbook = new SXSSFWorkbook(
new XSSFWorkbook(fileIn), 1000);
Sheet worksheet = workbook.getSheetAt(0);
Iterator<HashMap<String, Object>> it = data.iterator();
int i = rowNum;
while (it.hasNext()) {
Row row = worksheet.createRow(i);
int j = 0;
HashMap<String, Object> rowContent = it.next();
Iterator<String> it1 = fieldNames.iterator();
while (it1.hasNext()) {
Cell cell = row.createCell(j);
String key = it1.next();
Object o = rowContent.get(key);
if (o instanceof String) {
cell.setCellValue((String) o);
} else if (o instanceof Double) {
cell.setCellType(cell.CELL_TYPE_NUMERIC);
cell.setCellValue((Double) o);
}
j++;
}
i++;
}
fileIn.close();
FileOutputStream fileOut = new FileOutputStream(fileName);
workbook.write(fileOut);
fileOut.flush();
fileOut.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
我通过分批传递内容(以便保存在 jvm 内存上)并增加变量 rowNum 来附加到文件中。
据我了解,当我重新打开文件时
SXSSFWorkbook workbook = new SXSSFWorkbook(new XSSFWorkbook(fileIn),1000);
XSSWorkbook 的构造函数将整个文件重新加载到内存中,导致超出 gc 限制。
我浏览了http://poi.apache.org/spreadsheet/how-to.html但无法为我的用例找到合适的解决方案。
你们能否建议如何解决此问题以实现将行附加到工作簿的低内存占用?