Question

我是java的新手。我只是想了解如何处理堆内存溢出及其原因。有人可以帮我下面的代码为什么它会抛出这个错误。我怎么能避免它。

错误：

线程“main”中的异常java.lang.OutOfMemoryError：Java堆空间在java.util.Arrays.copyOf（Arrays.java:2361）at java.lang.AbstractStringBuilder.expandCapacity（AbstractStringBuilder.java:117）在 java.lang.AbstractStringBuilder.append（AbstractStringBuilder.java:406）在java.lang.StringBuffer.append（StringBuffer.java:237）at com.ugam.qa.tittle.XlsxToCsv.xlsx(XlsxToCsv.java:49）at at com.ugam.qa.tittle.XlsxToCsv.main（XlsxToCsv.java:77）

package com.ugam.qa.tittle;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.Iterator;

import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class XlsxToCsv {

    static void xlsx(File inputFile, File outputFile) {
        // For storing data into CSV files
        StringBuffer data = new StringBuffer();

        try {
            FileOutputStream fos = new FileOutputStream(outputFile);
            // Get the workbook object for XLSX file
            XSSFWorkbook wBook = new XSSFWorkbook(new FileInputStream(inputFile));
            // Get first sheet from the workbook
            XSSFSheet sheet = wBook.getSheetAt(0);
            Row row;
            Cell cell;
            // Iterate through each rows from first sheet
            Iterator<Row> rowIterator = sheet.iterator();

            while (rowIterator.hasNext()) {
                row = rowIterator.next();
                {
                // For each row, iterate through each columns
                Iterator<Cell> cellIterator = row.cellIterator();
                while (cellIterator.hasNext()) {

                    cell = cellIterator.next();

                    switch (cell.getCellType()) {
                        case Cell.CELL_TYPE_BOOLEAN:
                            data.append(cell.getBooleanCellValue() + ",");

                            break;
                        case Cell.CELL_TYPE_NUMERIC:
                            data.append(cell.getNumericCellValue() + ",");

                            break;
                        case Cell.CELL_TYPE_STRING:
                            data.append(cell.getStringCellValue() + ",");
                            break;

                        case Cell.CELL_TYPE_BLANK:
                            data.append("" + ",");
                            break;
                        default:
                            data.append(cell + ",");

                    }
                    data.append("\r\n");
                }}
            }

            fos.write(data.toString().getBytes());
            fos.close();

        } catch (Exception ioe) {
            ioe.printStackTrace();
        }
    }
    //testing the application 

    public static void main(String[] args) {
        //reading file from desktop
        File inputFile = new File("D:\\files\\listing\\test.xlsx");
        //writing excel data to csv 
        File outputFile = new File("D:\\files\\listing\\test1.csv");
        xlsx(inputFile, outputFile);

    }
}

Answer 1

增加堆是一种解决方案：java -Xmx<MegaBytes>M <YourClass>

更好的解决方案是使用更少的内存，这在您的情况下很容易：为什么要在将整个输出存储到流中之前将其存储在StringBuffer中？在您找到它们时，将每个部分直接写入流将会更加节省内存。

您的代码的另一个改进是使用FileWriter而不是FileOutputStream：它可以让您控制输出编码，并直接接受字符串，而无需您调用String#getBytes()。

Answer 2

首先（虽然与内存消耗无关），您正在创建一个文本文件，因此请使用FileWriter而不是FileOutputStream。

FileWriter writer = new FileWriter(outputFile);

其次，您正在内存中构建一个非常长的字符串。显然这会占用大量内存。最好构造程序，以便在读取输入文件时生成输出文件，而不会在内存中累积所有内容。例如，替换：

data.append(cell.getBooleanCellValue() + ",");

与

writer.write(cell.getBooleanCellValue() + ",");

Answer 3

只需使用

运行您的应用程序

java -Xmx<whatever value in megs/gigs> yourApp

Answer 4

在解析xlsx文件时我也遇到了同样的OOM问题......经过两天的挣扎，我终于找到了下面非常完美的代码;

此代码基于sjxlsx。它读取xlsx并存储在HSSF表中。

            // read the xlsx file
       SimpleXLSXWorkbook = new SimpleXLSXWorkbook(new File("C:/test.xlsx"));

        HSSFWorkbook hsfWorkbook = new HSSFWorkbook();

        org.apache.poi.ss.usermodel.Sheet hsfSheet = hsfWorkbook.createSheet();

        Sheet sheetToRead = workbook.getSheet(0, false);

        SheetRowReader reader = sheetToRead.newReader();
        Cell[] row;
        int rowPos = 0;
        while ((row = reader.readRow()) != null) {
            org.apache.poi.ss.usermodel.Row hfsRow = hsfSheet.createRow(rowPos);
            int cellPos = 0;
            for (Cell cell : row) {
                if(cell != null){
                    org.apache.poi.ss.usermodel.Cell hfsCell = hfsRow.createCell(cellPos);
                    hfsCell.setCellType(org.apache.poi.ss.usermodel.Cell.CELL_TYPE_STRING);
                    hfsCell.setCellValue(cell.getValue());
                }
                cellPos++;
            }
            rowPos++;
        }
        return hsfSheet;

超出堆内存，java

4 个答案: