Excel 2007 대용량 파일을 작성하는 교묘한 방법

1. 질문
수납장
POI excel 파일을 읽고 쓰는 것은 모두가 낯설지 않다고 믿는다.최근 프로젝트에서 excel 2007 형식의 템플릿을 읽고 이 excel에 10000개를 써서 출력해야 합니다.본인은 처음에poi의user모델로 excel을 썼지만 테스트를 해보니 메모리 소모가 매우 크고 (2G) 10분이 걸려야 excel의 생성을 완성할 수 있습니다.그럼 성능이 더 좋고 더 빠른 방법이 있을까요?ii는 이벤트 모델이지만 읽기만 지원하고 sxsff도 지원하며 쓰기만 지원합니다.우리는 원래 excel 템플릿에 많은 형식과 컨트롤이 있기 때문에 vba 매크로가 있기 때문에 읽기와 쓰기 기능을 동시에 갖추어야 한다.그래서 이 두 가지 방법은 모두 안 된다.
2. 교묘한 방법
본인이 여기서 찾은 방법:
http://vikramvkamath.blogspot.com/2010/07/writing-large-excel-files-excel-2007.html
원리: excel2007 형식 파일은 사실 zip 압축 패키지입니다.7zip 등 압축 소프트웨어로 열 수 있습니다.압축을 풀기 위한 구조는 다음과 같습니다.
/
- ..
- _rels
- .rels
- docProps
- app.xml
- core.xml
- xl
- _rels
- worksheets
- sheet1.xml
-
sheet2.xml
- sharedStrings.xml
- styles.xml
- workbook.xml
- [Content_Types].xml
위쪽 빨간색 sheet2.xml을 열어 보면 두 번째sheet 데이터 파일입니다.그래서 이 교묘한 방법은 자바로 이 xml 파일을 쓴 다음에 압축 가방에 다시 넣는 것이다.xml을 쓰면 xlsx를 쓰는 것보다 훨씬 빠르다.
이전 코드 예시, 원본은poi의 원본 코드 패키지를 다운로드하여 안에 있는 examples를 찾는 것입니다.가다
여기 보기

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.Calendar;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import java.util.zip.ZipOutputStream;

import org.apache.poi.ss.usermodel.DateUtil;
import org.apache.poi.ss.usermodel.IndexedColors;
import org.apache.poi.ss.util.CellReference;
import org.apache.poi.xssf.usermodel.XSSFCellStyle;
import org.apache.poi.xssf.usermodel.XSSFDataFormat;
import org.apache.poi.xssf.usermodel.XSSFFont;
import org.apache.poi.xssf.usermodel.XSSFSheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

/**
 * Demonstrates a workaround you can use to generate large workbooks and avoid OutOfMemory exception.
 *
 * The trick is as follows:
 * 1. create a template workbook, create sheets and global objects such as cell styles, number formats, etc.
 * 2. create an application that streams data in a text file
 * 3. Substitute the sheet in the template with the generated data
 *
 * @author Yegor Kozlov
 */
public class BigGridDemo {
    private static final String XML_ENCODING = "UTF-8";
    
    public static void main(String[] args) throws Exception {

        // Step 1. Create a template file. Setup sheets and workbook-level objects such as
        // cell styles, number formats, etc.

        XSSFWorkbook wb = new XSSFWorkbook();
        XSSFSheet sheet = wb.createSheet("Big Grid");

        Map<String, XSSFCellStyle> styles = createStyles(wb);
        //name of the zip entry holding sheet data, e.g. /xl/worksheets/sheet1.xml
        String sheetRef = sheet.getPackagePart().getPartName().getName();

        //save the template
        FileOutputStream os = new FileOutputStream("template.xlsx");
        wb.write(os);
        os.close();

        //Step 2. Generate XML file.
        File tmp = new File("sheet.xml");
        Writer fw = new OutputStreamWriter(new FileOutputStream(tmp), XML_ENCODING);
        generate(fw, styles);
        fw.close();

        //Step 3. Substitute the template entry with the generated data
        FileOutputStream out = new FileOutputStream("big-grid.xlsx");
        substitute(new File("template.xlsx"), tmp, sheetRef.substring(1), out);
        out.close();
    }

    /**
     * Create a library of cell styles.
     */
    private static Map<String, XSSFCellStyle> createStyles(XSSFWorkbook wb){
        Map<String, XSSFCellStyle> styles = new HashMap<String, XSSFCellStyle>();
        XSSFDataFormat fmt = wb.createDataFormat();

        XSSFCellStyle style1 = wb.createCellStyle();
        style1.setAlignment(XSSFCellStyle.ALIGN_RIGHT);
        style1.setDataFormat(fmt.getFormat("0.0%"));
        styles.put("percent", style1);

        XSSFCellStyle style2 = wb.createCellStyle();
        style2.setAlignment(XSSFCellStyle.ALIGN_CENTER);
        style2.setDataFormat(fmt.getFormat("0.0X"));
        styles.put("coeff", style2);

        XSSFCellStyle style3 = wb.createCellStyle();
        style3.setAlignment(XSSFCellStyle.ALIGN_RIGHT);
        style3.setDataFormat(fmt.getFormat("$#,##0.00"));
        styles.put("currency", style3);

        XSSFCellStyle style4 = wb.createCellStyle();
        style4.setAlignment(XSSFCellStyle.ALIGN_RIGHT);
        style4.setDataFormat(fmt.getFormat("mmm dd"));
        styles.put("date", style4);

        XSSFCellStyle style5 = wb.createCellStyle();
        XSSFFont headerFont = wb.createFont();
        headerFont.setBold(true);
        style5.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
        style5.setFillPattern(XSSFCellStyle.SOLID_FOREGROUND);
        style5.setFont(headerFont);
        styles.put("header", style5);

        return styles;
    }

    private static void generate(Writer out, Map<String, XSSFCellStyle> styles) throws Exception {

        Random rnd = new Random();
        Calendar calendar = Calendar.getInstance();

        SpreadsheetWriter sw = new SpreadsheetWriter(out);
        sw.beginSheet();

        //insert header row
        sw.insertRow(0);
        int styleIndex = styles.get("header").getIndex();
        sw.createCell(0, "Title", styleIndex);
        sw.createCell(1, "% Change", styleIndex);
        sw.createCell(2, "Ratio", styleIndex);
        sw.createCell(3, "Expenses", styleIndex);
        sw.createCell(4, "Date", styleIndex);

        sw.endRow();

        //write data rows
        for (int rownum = 1; rownum < 100000; rownum++) {
            sw.insertRow(rownum);

            sw.createCell(0, "Hello, " + rownum + "!");
            sw.createCell(1, (double)rnd.nextInt(100)/100, styles.get("percent").getIndex());
            sw.createCell(2, (double)rnd.nextInt(10)/10, styles.get("coeff").getIndex());
            sw.createCell(3, rnd.nextInt(10000), styles.get("currency").getIndex());
            sw.createCell(4, calendar, styles.get("date").getIndex());

            sw.endRow();

            calendar.roll(Calendar.DAY_OF_YEAR, 1);
        }
        sw.endSheet();
    }

    /**
     *
     * @param zipfile the template file
     * @param tmpfile the XML file with the sheet data
     * @param entry the name of the sheet entry to substitute, e.g. xl/worksheets/sheet1.xml
     * @param out the stream to write the result to
     */
	private static void substitute(File zipfile, File tmpfile, String entry, OutputStream out) throws IOException {
        ZipFile zip = new ZipFile(zipfile);

        ZipOutputStream zos = new ZipOutputStream(out);

        @SuppressWarnings("unchecked")
        Enumeration<ZipEntry> en = (Enumeration<ZipEntry>) zip.entries();
        while (en.hasMoreElements()) {
            ZipEntry ze = en.nextElement();
            if(!ze.getName().equals(entry)){
                zos.putNextEntry(new ZipEntry(ze.getName()));
                InputStream is = zip.getInputStream(ze);
                copyStream(is, zos);
                is.close();
            }
        }
        zos.putNextEntry(new ZipEntry(entry));
        InputStream is = new FileInputStream(tmpfile);
        copyStream(is, zos);
        is.close();

        zos.close();
    }

    private static void copyStream(InputStream in, OutputStream out) throws IOException {
        byte[] chunk = new byte[1024];
        int count;
        while ((count = in.read(chunk)) >=0 ) {
          out.write(chunk,0,count);
        }
    }

    /**
     * Writes spreadsheet data in a Writer.
     * (YK: in future it may evolve in a full-featured API for streaming data in Excel)
     */
    public static class SpreadsheetWriter {
        private final Writer _out;
        private int _rownum;

        public SpreadsheetWriter(Writer out){
            _out = out;
        }

        public void beginSheet() throws IOException {
            _out.write("<?xml version=\"1.0\" encoding=\""+XML_ENCODING+"\"?>" +
                    "<worksheet xmlns=\"http://schemas.openxmlformats.org/spreadsheetml/2006/main\">" );
            _out.write("<sheetData>
");
        }

        public void endSheet() throws IOException {
            _out.write("</sheetData>");
            _out.write("</worksheet>");
        }

        /**
         * Insert a new row
         *
         * @param rownum 0-based row number
         */
        public void insertRow(int rownum) throws IOException {
            _out.write("<row r=\""+(rownum+1)+"\">
");
            this._rownum = rownum;
        }

        /**
         * Insert row end marker
         */
        public void endRow() throws IOException {
            _out.write("</row>
");
        }

        public void createCell(int columnIndex, String value, int styleIndex) throws IOException {
            String ref = new CellReference(_rownum, columnIndex).formatAsString();
            _out.write("<c r=\""+ref+"\" t=\"inlineStr\"");
            if(styleIndex != -1) _out.write(" s=\""+styleIndex+"\"");
            _out.write(">");
            _out.write("<is><t>"+value+"</t></is>");
            _out.write("</c>");
        }

        public void createCell(int columnIndex, String value) throws IOException {
            createCell(columnIndex, value, -1);
        }

        public void createCell(int columnIndex, double value, int styleIndex) throws IOException {
            String ref = new CellReference(_rownum, columnIndex).formatAsString();
            _out.write("<c r=\""+ref+"\" t=\"n\"");
            if(styleIndex != -1) _out.write(" s=\""+styleIndex+"\"");
            _out.write(">");
            _out.write("<v>"+value+"</v>");
            _out.write("</c>");
        }

        public void createCell(int columnIndex, double value) throws IOException {
            createCell(columnIndex, value, -1);
        }

        public void createCell(int columnIndex, Calendar value, int styleIndex) throws IOException {
            createCell(columnIndex, DateUtil.getExcelDate(value, false), styleIndex);
        }
    }
}

3. 성능 비교
이 궤계를 사용한 후, excel 템플릿을 읽고 10000개의 기록을 excel에 써서 원래의 10분에서 3초로 만들었습니다!성능이 비약적이다.