POI解决读入Excel内存溢出

下面是结构图

在项目中遇到二十万行数据的excel用poi读取会内存溢出，一般方法是调大tomcat的内存，但是调到2048M还是会内存溢出报错

poi官网给了一种大批量数据读取的方法，通过把excel转化为csv,不一次读到内存中，这样就没问题了

下面是官方的example

package cn.com.ftms.utils;


import org.apache.poi.openxml4j.exceptions.OpenXML4JException;

/* ====================================================================
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import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintStream;

import javax.xml.parsers.ParserConfigurationException;

import org.apache.poi.openxml4j.exceptions.OpenXML4JException;
import org.apache.poi.openxml4j.opc.OPCPackage;
import org.apache.poi.openxml4j.opc.PackageAccess;
import org.apache.poi.ss.usermodel.DataFormatter;
import org.apache.poi.ss.util.CellAddress;
import org.apache.poi.ss.util.CellReference;
import org.apache.poi.util.SAXHelper;
import org.apache.poi.xssf.eventusermodel.ReadOnlySharedStringsTable;
import org.apache.poi.xssf.eventusermodel.XSSFReader;
import org.apache.poi.xssf.eventusermodel.XSSFSheetXMLHandler;
import org.apache.poi.xssf.eventusermodel.XSSFSheetXMLHandler.SheetContentsHandler;
import org.apache.poi.xssf.extractor.XSSFEventBasedExcelExtractor;
import org.apache.poi.xssf.model.StylesTable;
import org.apache.poi.xssf.usermodel.XSSFComment;
import org.xml.sax.ContentHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;

/**
 * A rudimentary XLSX -> CSV processor modeled on the
 * POI sample program XLS2CSVmra from the package
 * org.apache.poi.hssf.eventusermodel.examples.
 * As with the HSSF version, this tries to spot missing
 * rows and cells, and output empty entries for them.
 * <p/>
 * Data sheets are read using a SAX parser to keep the
 * memory footprint relatively small, so this should be
 * able to read enormous workbooks.  The styles table and
 * the shared-string table must be kept in memory.  The
 * standard POI styles table class is used, but a custom
 * (read-only) class is used for the shared string table
 * because the standard POI SharedStringsTable grows very
 * quickly with the number of unique strings.
 * <p/>
 * For a more advanced implementation of SAX event parsing
 * of XLSX files, see {@link XSSFEventBasedExcelExtractor}
 * and {@link XSSFSheetXMLHandler}. Note that for many cases,
 * it may be possible to simply use those with a custom
 * {@link SheetContentsHandler} and no SAX code needed of
 * your own!
 */
public class XLSX2CSV {
    /**
     * Uses the XSSF Event SAX helpers to do most of the work
     * of parsing the Sheet XML, and outputs the contents
     * as a (basic) CSV.
     */
    private class SheetToCSV implements SheetContentsHandler {
        private boolean firstCellOfRow = false;
        private int currentRow = -1;
        private int currentCol = -1;

        private void outputMissingRows(int number) {
            for (int i = 0; i < number; i++) {
                for (int j = 0; j < minColumns; j++) {
                    output.append(",");
                }
                output.append("
");
            }
        }

        @Override
        public void startRow(int rowNum) {
            // If there were gaps, output the missing rows
            outputMissingRows(rowNum - currentRow - 1);
            // Prepare for this row
            firstCellOfRow = true;
            currentRow = rowNum;
            currentCol = -1;
        }

        @Override
        public void endRow(int rowNum) {
            // Ensure the minimum number of columns
            for (int i = currentCol; i < minColumns; i++) {
                output.append(",");
            }
            output.append("
");
        }

        @Override
        public void cell(String cellReference, String formattedValue,
                         XSSFComment comment) {
            if (firstCellOfRow) {
                firstCellOfRow = false;
            } else {
                output.append(",");
            }

            // gracefully handle missing CellRef here in a similar way as XSSFCell does
            if (cellReference == null) {
                cellReference = new CellAddress(currentRow, currentCol).formatAsString();
            }

            // Did we miss any cells?
            int thisCol = (new CellReference(cellReference)).getCol();
            int missedCols = thisCol - currentCol - 1;
            for (int i = 0; i < missedCols; i++) {
                output.append(",");
            }
            currentCol = thisCol;

            // Number or string?
            try {
                Double.parseDouble(formattedValue);
                output.append(formattedValue);
            } catch (NumberFormatException e) {
                output.append(""");
                output.append(formattedValue);
                output.append(""");
            }
        }

        @Override
        public void headerFooter(String text, boolean isHeader, String tagName) {
            // Skip, no headers or footers in CSV
        }
    }


    ///////////////////////////////////////

    private final OPCPackage xlsxPackage;

    /**
     * Number of columns to read starting with leftmost
     */
    private final int minColumns;

    /**
     * Destination for data
     */
    private final PrintStream output;

    /**
     * Creates a new XLSX -> CSV converter
     *
     * @param pkg        The XLSX package to process
     * @param output     The PrintStream to output the CSV to
     * @param minColumns The minimum number of columns to output, or -1 for no minimum
     */
    public XLSX2CSV(OPCPackage pkg, PrintStream output, int minColumns) {
        this.xlsxPackage = pkg;
        this.output = output;
        this.minColumns = minColumns;
    }

    /**
     * Parses and shows the content of one sheet
     * using the specified styles and shared-strings tables.
     *
     * @param styles
     * @param strings
     * @param sheetInputStream
     */
    public void processSheet(
            StylesTable styles,
            ReadOnlySharedStringsTable strings,
            SheetContentsHandler sheetHandler,
            InputStream sheetInputStream)
            throws IOException, ParserConfigurationException, SAXException {
        DataFormatter formatter = new DataFormatter();
        InputSource sheetSource = new InputSource(sheetInputStream);
        try {
            XMLReader sheetParser = SAXHelper.newXMLReader();
            ContentHandler handler = new XSSFSheetXMLHandler(
                    styles, null, strings, sheetHandler, formatter, false);
            sheetParser.setContentHandler(handler);
            sheetParser.parse(sheetSource);
        } catch (ParserConfigurationException e) {
            throw new RuntimeException("SAX parser appears to be broken - " + e.getMessage());
        }
    }

    /**
     * Initiates the processing of the XLS workbook file to CSV.
     *
     * @throws IOException
     * @throws OpenXML4JException
     * @throws ParserConfigurationException
     * @throws SAXException
     */
    public void process()
            throws IOException, OpenXML4JException, ParserConfigurationException, SAXException {
        ReadOnlySharedStringsTable strings = new ReadOnlySharedStringsTable(this.xlsxPackage);
        XSSFReader xssfReader = new XSSFReader(this.xlsxPackage);
        StylesTable styles = xssfReader.getStylesTable();
        XSSFReader.SheetIterator iter = (XSSFReader.SheetIterator) xssfReader.getSheetsData();
        int index = 0;
        while (iter.hasNext()) {
            InputStream stream = iter.next();
            String sheetName = iter.getSheetName();
            this.output.println();
            this.output.println(sheetName + " [index=" + index + "]:");
            processSheet(styles, strings, new SheetToCSV(), stream);
            stream.close();
            ++index;
        }
    }

    public static void main(String[] args) throws Exception {
      /*  if (args.length < 1) {
            System.err.println("Use:");
            System.err.println("  XLSX2CSV <xlsx file> [min columns]");
            return;
        }*/

        File xlsxFile = new File("F:\8月数据.xlsx");
        if (!xlsxFile.exists()) {
            System.err.println("Not found or not a file: " + xlsxFile.getPath());
            return;
        }

        int minColumns = -1;
        if (args.length >= 2)
            minColumns = Integer.parseInt(args[1]);

        // The package open is instantaneous, as it should be.
        OPCPackage p = OPCPackage.open(xlsxFile.getPath(), PackageAccess.READ);
        XLSX2CSV xlsx2csv = new XLSX2CSV(p, System.out, minColumns);
        xlsx2csv.process();
        p.close();
    }
}

参考地址：点击打开链接https://svn.apache.org/repos/asf/poi/trunk/src/examples/src/org/apache/poi/xssf/eventusermodel/XLSX2CSV.java