POI导出大Excel问题

前段时间，做POI导出的时候，应为数据量大（十万条数据），所以总是出现OOM错误，在网上找到了解决办法，大数据量导出Excel的方案：http://devbbs.doit.com.cn/redirect.php?tid=46&goto=lastpost
解决大批量数据导出Excel产生内存溢出的方案：http://cnaning.iteye.com/blog/347158
解决大批量数据导出Excel产生内存溢出的方案（二）：http://cnaning.iteye.com/blog/347160

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.log4j.Logger;
import org.apache.poi.hssf.model.Sheet;
import org.apache.poi.hssf.model.Workbook;
import org.apache.poi.hssf.record.CellValueRecordInterface;
import org.apache.poi.hssf.record.LabelRecord;
import org.apache.poi.hssf.record.LabelSSTRecord;
import org.apache.poi.hssf.record.Record;
import org.apache.poi.hssf.record.RowRecord;
import org.apache.poi.hssf.record.SSTRecord;
import org.apache.poi.hssf.record.UnicodeString;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.struts.taglib.html.RewriteTag;

@SuppressWarnings("unchecked")
public class XlsMergeUtil {
    private static Logger logger = Logger.getLogger(XlsMergeUtil.class);

    /**
     * 将多个Xls文件合并为一个，适用于只有一个sheet，并且格式相同的文档
     *
     * @param inputs
     *            输入的Xls文件，第一个XLS文件必须给出足够sheet空间 例如，总共200000行数据，第一个文件至少3个空白sheet
     * @param out
     *            输出文件
     */
    public static void merge(InputStream[] inputs, OutputStream out) {
        if (inputs == null || inputs.length <= 1) {
            throw new IllegalArgumentException("没有传入输入流数组,或只有一个输入流.");
        }

        List<Record> rootRecords = getRecords(inputs[0]);
        Workbook workbook = Workbook.createWorkbook(rootRecords);
        List<Sheet> sheets = getSheets(workbook, rootRecords);
        if (sheets == null || sheets.size() == 0) {
            throw new IllegalArgumentException("第一篇文档的格式错误，必须有至少一个sheet");
        }
        // 以第一篇文档的第一个sheet为根，以后的数据都追加在这个sheet后面
        Sheet rootSheet = sheets.get(0);
        int rootRows = getRowsOfSheet(rootSheet); // 记录第一篇文档的行数，以后的行数在此基础上增加
        rootSheet.setLoc(rootSheet.getDimsLoc());
        Map<Integer, Integer> map = new HashMap(10000);
        int sheetIndex = 0;

        for (int i = 1; i < inputs.length; i++) { // 从第二篇开始遍历
            List<Record> records = getRecords(inputs[i]);
            // 达到最大行数限制，换一个sheet
            if (getRows(records) + rootRows >= RowRecord.MAX_ROW_NUMBER) {
                if ((++sheetIndex) > (sheets.size() - 1)) {
                    logger.warn("第一个文档给出的sheets小于需要的数量，部分数据未能合并.");
                    break;
                }
                rootSheet = sheets.get(sheetIndex);
                rootRows = getRowsOfSheet(rootSheet);
                rootSheet.setLoc(rootSheet.getDimsLoc());
                logger.debug("切换Sheet" + sheetIndex + "");
            }
            int rowsOfCurXls = 0;
            // 遍历当前文档的每一个record
            for (Iterator itr = records.iterator(); itr.hasNext();) {
                Record record = (Record) itr.next();
                if (record.getSid() == RowRecord.sid) { // 如果是RowRecord
                    RowRecord rowRecord = (RowRecord) record;
                    // 调整行号
                    rowRecord.setRowNumber(rootRows + rowRecord.getRowNumber());
                    rootSheet.addRow(rowRecord); // 追加Row
                    rowsOfCurXls++; // 记录当前文档的行数
                }
                // SST记录，SST保存xls文件中唯一的String，各个String都是对应着SST记录的索引
                else if (record.getSid() == SSTRecord.sid) {
                    SSTRecord sstRecord = (SSTRecord) record;
                    for (int j = 0; j < sstRecord.getNumUniqueStrings(); j++) {
                        int index = workbook.addSSTString(sstRecord
                                .getString(j));
                        // 记录原来的索引和现在的索引的对应关系
                        map.put(Integer.valueOf(j), Integer.valueOf(index));
                    }
                } else if (record.getSid() == LabelSSTRecord.sid) {
                    LabelSSTRecord label = (LabelSSTRecord) record;
                    // 调整SST索引的对应关系
                    label.setSSTIndex(map.get(Integer.valueOf(label
                            .getSSTIndex())));
                }
                // 追加ValueCell
                if (record instanceof CellValueRecordInterface) {
                    CellValueRecordInterface cell = (CellValueRecordInterface) record;
                    int cellRow = cell.getRow() + rootRows;
                    cell.setRow(cellRow);
                    rootSheet.addValueRecord(cellRow, cell);
                }
            }
            rootRows += rowsOfCurXls;
        }

        byte[] data = getBytes(workbook, sheets.toArray(new Sheet[0]));
        write(out, data);
    }

    static void write(OutputStream out, byte[] data) {
        POIFSFileSystem fs = new POIFSFileSystem();
        // Write out the Workbook stream
        try {
            fs.createDocument(new ByteArrayInputStream(data), "Workbook");
            fs.writeFilesystem(out);
            out.flush();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                out.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    static List<Sheet> getSheets(Workbook workbook, List records) {
        int recOffset = workbook.getNumRecords();
        int sheetNum = 0;

        // convert all LabelRecord records to LabelSSTRecord
        convertLabelRecords(records, recOffset, workbook);
        List<Sheet> sheets = new ArrayList();
        while (recOffset < records.size()) {
            Sheet sh = Sheet.createSheet(records, sheetNum++, recOffset);

            recOffset = sh.getEofLoc() + 1;
            if (recOffset == 1) {
                break;
            }
            sheets.add(sh);
        }
        return sheets;
    }

    static int getRows(List<Record> records) {
        int row = 0;
        for (Iterator itr = records.iterator(); itr.hasNext();) {
            Record record = (Record) itr.next();
            if (record.getSid() == RowRecord.sid) {
                row++;
            }
        }
        return row;
    }

    static int getRowsOfSheet(Sheet sheet) {
        int rows = 0;
        sheet.setLoc(0);
        while (sheet.getNextRow() != null) {
            rows++;
        }
        return rows;
    }

    @SuppressWarnings("deprecation")
    static List<Record> getRecords(InputStream input) {
        try {
            POIFSFileSystem poifs = new POIFSFileSystem(input);
            InputStream stream = poifs.getRoot().createDocumentInputStream(
                    "Workbook");
            return org.apache.poi.hssf.record.RecordFactory.createRecords(stream);
        } catch (IOException e) {
            logger.error("IO异常：" + e.getMessage() + "");
            e.printStackTrace();
        }
        return Collections.EMPTY_LIST;
    }

    static void convertLabelRecords(List records, int offset, Workbook workbook) {

        for (int k = offset; k < records.size(); k++) {
            Record rec = (Record) records.get(k);

            if (rec.getSid() == LabelRecord.sid) {
                LabelRecord oldrec = (LabelRecord) rec;

                records.remove(k);
                LabelSSTRecord newrec = new LabelSSTRecord();
                int stringid = workbook.addSSTString(new UnicodeString(oldrec
                        .getValue()));

                newrec.setRow(oldrec.getRow());
                newrec.setColumn(oldrec.getColumn());
                newrec.setXFIndex(oldrec.getXFIndex());
                newrec.setSSTIndex(stringid);
                records.add(k, newrec);
            }
        }
    }

    public static byte[] getBytes(Workbook workbook, Sheet[] sheets) {
        // HSSFSheet[] sheets = getSheets();
        int nSheets = sheets.length;

        // before getting the workbook size we must tell the sheets that
        // serialization is about to occur.
        for (int i = 0; i < nSheets; i++) {
            sheets[i].preSerialize();
        }

        int totalsize = workbook.getSize();
        // pre-calculate all the sheet sizes and set BOF indexes
        int[] estimatedSheetSizes = new int[nSheets];
        for (int k = 0; k < nSheets; k++) {
            workbook.setSheetBof(k, totalsize);
            int sheetSize = sheets[k].getSize();
            estimatedSheetSizes[k] = sheetSize;
            totalsize += sheetSize;
        }
        logger.debug("分配内存" + totalsize + "bytes");
        byte[] retval = new byte[totalsize];
        int pos = workbook.serialize(0, retval);
        for (int k = 0; k < nSheets; k++) {
            int serializedSize = sheets[k].serialize(pos, retval);
            if (serializedSize != estimatedSheetSizes[k]) {
                // Wrong offset values have been passed in the call to
                // setSheetBof() above.
                // For books with more than one sheet, this discrepancy would
                // cause excel
                // to report errors and loose data while reading the workbook
                throw new IllegalStateException(
                        "Actual serialized sheet size (" + serializedSize
                                + ") differs from pre-calculated size ("
                                + estimatedSheetSizes[k] + ") for sheet (" + k
                                + ")");
                // write mis-aligned offsets either
            }
            pos += serializedSize;
        }
        return retval;
    }

}