java - 堆内存不足，java

Question

我是java新手。我只是想了解如何处理堆内存溢出及其原因。有人可以在下面的代码中帮助我为什么会抛出此错误。我怎么能避免呢。

错误:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space at java.util.Arrays.copyOf(Arrays.java:2361) at java.lang.AbstractStringBuilder.expandCapacity(AbstractStringBuilder.java:117) at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:406) at java.lang.StringBuffer.append(StringBuffer.java:237) at com.ugam.qa.tittle.XlsxToCsv.xlsx(XlsxToCsv.java:49) 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，这对您来说很容易:为什么要将整个输出存储在 StringBuffer 中？在把它扔进你的流之前？当您找到它们时，将每个部分直接写入流中会提高内存效率。

代码的另一个改进是使用 FileWriter而不是 FileOutputStream : 它可以让你控制输出编码，并直接接受字符串而不需要你调用 String#getBytes() .