How to convert HSSFWorkbook to XSSFWorkbook using Apache POI?

//Added xbean-2.3.0.jar/xmlbeans-2.3.0.jar,poi-ooxml-3.7-20101029.jarpoi-ooxml-schemas-3.7-beta1.jar,


import java.io.*;
import java.util.*;

import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xssf.usermodel.*;

public class Xlsx2Xls {

private File path = new File("c:/Integration-TestCases.xls");
private ArrayList<File> inputFiles = new ArrayList<File>();

private int lastColumn = 0;
private HashMap<Integer, HSSFCellStyle> styleMap = new HashMap();

private void getInputFiles() {
    String call = "getInputFiles ";
    if (this.path.isFile()) {
        if (this.path.getAbsolutePath().endsWith(".xls")
                && !new File(this.path.getAbsolutePath() + "x").exists())
            this.inputFiles.add(this.path);
        else {
            System.out
                    .println("Datei endet nicht mit .xls oder XLSX-Datei existiert bereits");
        }
    } else
        for (File f : this.path.listFiles(new FilenameFilter() {
            // anonyme innere Klasse

            @Override
            public boolean accept(File dir, String name) {
                if (name.endsWith(".xls"))
                    return true;
                return false;
            }

        })) {
            if (!new File(f.getAbsoluteFile() + "x").exists()) {
                this.inputFiles.add(f);
            }
        }
    System.out
            .println(call + "Dateien gefunden: " + this.inputFiles.size());
    System.out.println(call + "abgeschlossen");
}

private HSSFWorkbook getWorkBook(File f) throws FileNotFoundException,
        IOException {
    System.out.println("getWorkBook lese " + f.getAbsolutePath());
    POIFSFileSystem fs = new POIFSFileSystem(new BufferedInputStream(
            new FileInputStream(f)));
    HSSFWorkbook workbook = new HSSFWorkbook(fs);
    System.out.println("getWorkBook abgeschlossen");
    return workbook;
}

private void transformXSSF(XSSFWorkbook workbookOld ,HSSFWorkbook workbookNew) {
    String call = "transform ";
    System.out.println(call + "Workbook");
    HSSFSheet sheetNew;
    XSSFSheet sheetOld;
    //TODO::workbookNew.setForceFormulaRecalculation(workbookOld.getForceFormulaRecalculation());
    // workbookNew.setHidden(workbookOld.isHidden()); //[email protected] -
    // von Apache noch nicht implementiert
    workbookNew.setMissingCellPolicy(workbookOld.getMissingCellPolicy());

    for (int i = 0; i < workbookOld.getNumberOfSheets(); i++) {
        sheetOld =  workbookOld.getSheetAt(i);
        sheetNew = workbookNew.getSheet(sheetOld.getSheetName());
        System.out.println(call + "Sheet Name: " + sheetOld.getSheetName());
        sheetNew = workbookNew.createSheet(sheetOld.getSheetName());
        this.transform(workbookOld,workbookNew,sheetOld, sheetNew);
    }
    System.out.println(call + "Styles size: "        + this.styleMap.size());
    System.out.println(call + "abgeschlossen");
}



    private void transform(XSSFWorkbook workbookOld ,HSSFWorkbook workbookNew,XSSFSheet sheetOld, HSSFSheet sheetNew) {
        System.out.println("transform Sheet");

        sheetNew.setDisplayFormulas(sheetOld.isDisplayFormulas());
        sheetNew.setDisplayGridlines(sheetOld.isDisplayGridlines());
        sheetNew.setDisplayGuts(sheetOld.getDisplayGuts());
        sheetNew.setDisplayRowColHeadings(sheetOld.isDisplayRowColHeadings());
        sheetNew.setDisplayZeros(sheetOld.isDisplayZeros());
        sheetNew.setFitToPage(sheetOld.getFitToPage());
        //
        //TODO::sheetNew.setForceFormulaRecalculation(sheetOld.getForceFormulaRecalculation());
        sheetNew.setHorizontallyCenter(sheetOld.getHorizontallyCenter());
        sheetNew.setMargin(Sheet.BottomMargin,
                sheetOld.getMargin(Sheet.BottomMargin));
        sheetNew.setMargin(Sheet.FooterMargin,
                sheetOld.getMargin(Sheet.FooterMargin));
        sheetNew.setMargin(Sheet.HeaderMargin,
                sheetOld.getMargin(Sheet.HeaderMargin));
        sheetNew.setMargin(Sheet.LeftMargin,
                sheetOld.getMargin(Sheet.LeftMargin));
        sheetNew.setMargin(Sheet.RightMargin,
                sheetOld.getMargin(Sheet.RightMargin));
        sheetNew.setMargin(Sheet.TopMargin, sheetOld.getMargin(Sheet.TopMargin));
        sheetNew.setPrintGridlines(sheetNew.isPrintGridlines());
        sheetNew.setRightToLeft(sheetNew.isRightToLeft());
        sheetNew.setRowSumsBelow(sheetNew.getRowSumsBelow());
        sheetNew.setRowSumsRight(sheetNew.getRowSumsRight());
        sheetNew.setVerticallyCenter(sheetOld.getVerticallyCenter());

        HSSFRow rowNew;
        for (Row row : sheetOld) {
            rowNew = sheetNew.createRow(row.getRowNum());
            if (rowNew != null)
                this.transform(workbookOld,workbookNew,(XSSFRow) row, rowNew);
        }

        for (int i = 0; i < this.lastColumn; i++) {
            sheetNew.setColumnWidth(i, sheetOld.getColumnWidth(i));
            sheetNew.setColumnHidden(i, sheetOld.isColumnHidden(i));
        }

        for (int i = 0; i < sheetOld.getNumMergedRegions(); i++) {
            CellRangeAddress merged = sheetOld.getMergedRegion(i);
            sheetNew.addMergedRegion(merged);
        }
    }



    private void transform(XSSFWorkbook workbookOld ,HSSFWorkbook workbookNew,XSSFRow rowOld, HSSFRow rowNew) {
        HSSFCell cellNew;
        rowNew.setHeight(rowOld.getHeight());
        //TODO::if (rowOld.getRowStyle() != null) {
            /*Integer hash = rowOld.getRowStyle().hashCode();
            if (!this.styleMap.containsKey(hash))
                this.transform(workbookOld,workbookNew,hash, (XSSFCellStyle)rowOld.getRowStyle(),(HSSFCellStyle)workbookNew.createCellStyle());
            rowNew.setRowStyle(this.styleMap.get(hash));
        }*/
        for (Cell cell : rowOld) {
            cellNew = rowNew.createCell(cell.getColumnIndex(),
                    cell.getCellType());
            if (cellNew != null)
                this.transform(workbookOld,workbookNew,(XSSFCell) cell, cellNew);
        }
        this.lastColumn = Math.max(this.lastColumn, rowOld.getLastCellNum());
    }




    private void transform(XSSFWorkbook workbookOld,HSSFWorkbook workbookNew,XSSFCell cellOld, HSSFCell cellNew) {
        cellNew.setCellComment(cellOld.getCellComment());

        Integer hash = cellOld.getCellStyle().hashCode();
        if (this.styleMap!=null && !this.styleMap.containsKey(hash)) {
            this.transform(workbookOld,workbookNew,hash, cellOld.getCellStyle(),(HSSFCellStyle)workbookNew.createCellStyle());
        }
        cellNew.setCellStyle(this.styleMap.get(hash));

        switch (cellOld.getCellType()) {
        case Cell.CELL_TYPE_BLANK:
            break;
        case Cell.CELL_TYPE_BOOLEAN:
            cellNew.setCellValue(cellOld.getBooleanCellValue());
            break;
        case Cell.CELL_TYPE_ERROR:
            cellNew.setCellValue(cellOld.getErrorCellValue());
            break;
        case Cell.CELL_TYPE_FORMULA:
            cellNew.setCellValue(cellOld.getCellFormula());
            break;
        case Cell.CELL_TYPE_NUMERIC:
            cellNew.setCellValue(cellOld.getNumericCellValue());
            break;
        case Cell.CELL_TYPE_STRING:
            cellNew.setCellValue(cellOld.getStringCellValue());
            break;
        default:
            System.out.println("transform: Unbekannter Zellentyp "
                    + cellOld.getCellType());
        }
    }




    private void transform(XSSFWorkbook workbookOld,HSSFWorkbook workbookNew,Integer hash, XSSFCellStyle styleOld,
            HSSFCellStyle styleNew) {
        styleNew.setAlignment(styleOld.getAlignment());
        styleNew.setBorderBottom(styleOld.getBorderBottom());
        styleNew.setBorderLeft(styleOld.getBorderLeft());
        styleNew.setBorderRight(styleOld.getBorderRight());
        styleNew.setBorderTop(styleOld.getBorderTop());
         styleNew.setDataFormat(this.transform( workbookOld, workbookNew,styleOld.getDataFormat()));
        styleNew.setFillBackgroundColor(styleOld.getFillBackgroundColor());
        styleNew.setFillForegroundColor(styleOld.getFillForegroundColor());
        styleNew.setFillPattern(styleOld.getFillPattern());
        styleNew.setFont(this.transform(workbookNew,(XSSFFont)styleOld.getFont()));
        styleNew.setHidden(styleOld.getHidden());
        styleNew.setIndention(styleOld.getIndention());
        styleNew.setLocked(styleOld.getLocked());
        styleNew.setVerticalAlignment(styleOld.getVerticalAlignment());
        styleNew.setWrapText(styleOld.getWrapText());
        this.styleMap.put(hash, styleNew);
    }

private short transform(XSSFWorkbook workbookOld,HSSFWorkbook workbookNew,short index) {
    DataFormat formatOld = workbookOld.createDataFormat();
    DataFormat formatNew = workbookNew.createDataFormat();
    return formatNew.getFormat(formatOld.getFormat(index));
}


    private HSSFFont transform(HSSFWorkbook workbookNew,XSSFFont fontOld) {
        HSSFFont fontNew = workbookNew.createFont();
        fontNew.setBoldweight(fontOld.getBoldweight());
        fontNew.setCharSet(fontOld.getCharSet());
        fontNew.setColor(fontOld.getColor());
        fontNew.setFontName(fontOld.getFontName());
        fontNew.setFontHeight(fontOld.getFontHeight());
        fontNew.setItalic(fontOld.getItalic());
        fontNew.setStrikeout(fontOld.getStrikeout());
        fontNew.setTypeOffset(fontOld.getTypeOffset());
        fontNew.setUnderline(fontOld.getUnderline());
        return fontNew;
    }

public static void main(String[] args) throws Exception{
    Xlsx2Xls xls=new Xlsx2Xls(); 
    //xls.transform();
     InputStream isXlsx = new FileInputStream("c:/OTD.xlsx");
     XSSFWorkbook workbookOld     = new XSSFWorkbook(isXlsx);

    String dest="c:/OTD1.xls";

    FileOutputStream out = new FileOutputStream(dest);
    HSSFWorkbook workbookNew = new HSSFWorkbook();
    xls.transformXSSF( workbookOld , workbookNew) ;    
    workbookNew.write(out);

    out.close();

//    InputStream isXls = new FileInputStream("c:/OTD1.xls");
//    HSSFWorkbook workbookNew     = new HSSFWorkbook(isXls);



}
}

//Added xbean-2.3.0.jar/xmlbeans-2.3.0.jar,poi-ooxml-3.7-20101029.jarpoi-ooxml-schemas-3.7-beta1.jar,
import java.io.*;
import java.util.*;

import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xssf.usermodel.*;

public class Xls2Xlsx {

private File path = new File("c:/Integration-TestCases.xls");
private ArrayList<File> inputFiles = new ArrayList<File>();

private int lastColumn = 0;
private HashMap<Integer, XSSFCellStyle> styleMap = new HashMap();

private void getInputFiles() {
    String call = "getInputFiles ";
    if (this.path.isFile()) {
        if (this.path.getAbsolutePath().endsWith(".xls")
                && !new File(this.path.getAbsolutePath() + "x").exists())
            this.inputFiles.add(this.path);
        else {
            System.out
                    .println("Datei endet nicht mit .xls oder XLSX-Datei existiert bereits");
        }
    } else
        for (File f : this.path.listFiles(new FilenameFilter() {
            // anonyme innere Klasse

            @Override
            public boolean accept(File dir, String name) {
                if (name.endsWith(".xls"))
                    return true;
                return false;
            }

        })) {
            if (!new File(f.getAbsoluteFile() + "x").exists()) {
                this.inputFiles.add(f);
            }
        }
    System.out
            .println(call + "Dateien gefunden: " + this.inputFiles.size());
    System.out.println(call + "abgeschlossen");
}

private HSSFWorkbook getWorkBook(File f) throws FileNotFoundException,
        IOException {
    System.out.println("getWorkBook lese " + f.getAbsolutePath());
    POIFSFileSystem fs = new POIFSFileSystem(new BufferedInputStream(
            new FileInputStream(f)));
    HSSFWorkbook workbook = new HSSFWorkbook(fs);
    System.out.println("getWorkBook abgeschlossen");
    return workbook;
}

private void transformHSSF(HSSFWorkbook workbookOld ,XSSFWorkbook workbookNew) {
    String call = "transform ";
    System.out.println(call + "Workbook");
    XSSFSheet sheetNew;
    HSSFSheet sheetOld;
    //TODO::workbookNew.setForceFormulaRecalculation(workbookOld.getForceFormulaRecalculation());
    // workbookNew.setHidden(workbookOld.isHidden()); //[email protected] -
    // von Apache noch nicht implementiert
    workbookNew.setMissingCellPolicy(workbookOld.getMissingCellPolicy());

    for (int i = 0; i < workbookOld.getNumberOfSheets(); i++) {
        sheetOld =  workbookOld.getSheetAt(i);
        sheetNew = workbookNew.getSheet(sheetOld.getSheetName());
        System.out.println(call + "Sheet Name: " + sheetOld.getSheetName());
        sheetNew = workbookNew.createSheet(sheetOld.getSheetName());
        this.transform(workbookOld,workbookNew,sheetOld, sheetNew);
    }
    System.out.println(call + "Styles size: "        + this.styleMap.size());
    System.out.println(call + "abgeschlossen");
}



    private void transform(HSSFWorkbook workbookOld ,XSSFWorkbook workbookNew,HSSFSheet sheetOld, XSSFSheet sheetNew) {
        System.out.println("transform Sheet");

        sheetNew.setDisplayFormulas(sheetOld.isDisplayFormulas());
        sheetNew.setDisplayGridlines(sheetOld.isDisplayGridlines());
        sheetNew.setDisplayGuts(sheetOld.getDisplayGuts());
        sheetNew.setDisplayRowColHeadings(sheetOld.isDisplayRowColHeadings());
        sheetNew.setDisplayZeros(sheetOld.isDisplayZeros());
        sheetNew.setFitToPage(sheetOld.getFitToPage());
        //
        //TODO::sheetNew.setForceFormulaRecalculation(sheetOld.getForceFormulaRecalculation());
        sheetNew.setHorizontallyCenter(sheetOld.getHorizontallyCenter());
        sheetNew.setMargin(Sheet.BottomMargin,
                sheetOld.getMargin(Sheet.BottomMargin));
        sheetNew.setMargin(Sheet.FooterMargin,
                sheetOld.getMargin(Sheet.FooterMargin));
        sheetNew.setMargin(Sheet.HeaderMargin,
                sheetOld.getMargin(Sheet.HeaderMargin));
        sheetNew.setMargin(Sheet.LeftMargin,
                sheetOld.getMargin(Sheet.LeftMargin));
        sheetNew.setMargin(Sheet.RightMargin,
                sheetOld.getMargin(Sheet.RightMargin));
        sheetNew.setMargin(Sheet.TopMargin, sheetOld.getMargin(Sheet.TopMargin));
        sheetNew.setPrintGridlines(sheetNew.isPrintGridlines());
        //TODO::sheetNew.setRightToLeft(sheetNew.isRightToLeft());
        sheetNew.setRowSumsBelow(sheetNew.getRowSumsBelow());
        sheetNew.setRowSumsRight(sheetNew.getRowSumsRight());
        sheetNew.setVerticallyCenter(sheetOld.getVerticallyCenter());

        XSSFRow rowNew;
        for (Row row : sheetOld) {
            rowNew = sheetNew.createRow(row.getRowNum());
            if (rowNew != null)
                this.transform(workbookOld,workbookNew,(HSSFRow) row, rowNew);
        }

        for (int i = 0; i < this.lastColumn; i++) {
            sheetNew.setColumnWidth(i, sheetOld.getColumnWidth(i));
            sheetNew.setColumnHidden(i, sheetOld.isColumnHidden(i));
        }

        for (int i = 0; i < sheetOld.getNumMergedRegions(); i++) {
            CellRangeAddress merged = sheetOld.getMergedRegion(i);
            sheetNew.addMergedRegion(merged);
        }
    }



    private void transform(HSSFWorkbook workbookOld ,XSSFWorkbook workbookNew,HSSFRow rowOld, XSSFRow rowNew) {
        XSSFCell cellNew;
        rowNew.setHeight(rowOld.getHeight());
        //TODO::if (rowOld.getRowStyle() != null) {
            /*Integer hash = rowOld.getRowStyle().hashCode();
            if (!this.styleMap.containsKey(hash))
                this.transform(workbookOld,workbookNew,hash, (XSSFCellStyle)rowOld.getRowStyle(),(HSSFCellStyle)workbookNew.createCellStyle());
            rowNew.setRowStyle(this.styleMap.get(hash));
        }*/
        for (Cell cell : rowOld) {
            cellNew = rowNew.createCell(cell.getColumnIndex(), cell.getCellType());
            if (cellNew != null)
                this.transform(workbookOld,workbookNew,(HSSFCell) cell, cellNew);
        }
        this.lastColumn = Math.max(this.lastColumn, rowOld.getLastCellNum());
    }




    private void transform(HSSFWorkbook workbookOld,XSSFWorkbook workbookNew,HSSFCell cellOld,XSSFCell cellNew) {
        cellNew.setCellComment(cellOld.getCellComment());

        Integer hash = cellOld.getCellStyle().hashCode();
        if (this.styleMap!=null && !this.styleMap.containsKey(hash)) {
            this.transform(workbookOld,workbookNew,hash, cellOld.getCellStyle(),(XSSFCellStyle)workbookNew.createCellStyle());
        }
        cellNew.setCellStyle(this.styleMap.get(hash));

        switch (cellOld.getCellType()) {
        case Cell.CELL_TYPE_BLANK:
            break;
        case Cell.CELL_TYPE_BOOLEAN:
            cellNew.setCellValue(cellOld.getBooleanCellValue());
            break;
        case Cell.CELL_TYPE_ERROR:
            cellNew.setCellValue(cellOld.getErrorCellValue());
            break;
        case Cell.CELL_TYPE_FORMULA:
            cellNew.setCellValue(cellOld.getCellFormula());
            break;
        case Cell.CELL_TYPE_NUMERIC:
            cellNew.setCellValue(cellOld.getNumericCellValue());
            break;
        case Cell.CELL_TYPE_STRING:
            cellNew.setCellValue(cellOld.getStringCellValue());
            break;
        default:
            System.out.println("transform: Unbekannter Zellentyp "
                    + cellOld.getCellType());
        }
    }




    private void transform(HSSFWorkbook workbookOld,XSSFWorkbook workbookNew,Integer hash, HSSFCellStyle styleOld,
            XSSFCellStyle styleNew) {
        styleNew.setAlignment(styleOld.getAlignment());
        styleNew.setBorderBottom(styleOld.getBorderBottom());
        styleNew.setBorderLeft(styleOld.getBorderLeft());
        styleNew.setBorderRight(styleOld.getBorderRight());
        styleNew.setBorderTop(styleOld.getBorderTop());
         styleNew.setDataFormat(this.transform( workbookOld, workbookNew,styleOld.getDataFormat()));
        styleNew.setFillBackgroundColor(styleOld.getFillBackgroundColor());
        styleNew.setFillForegroundColor(styleOld.getFillForegroundColor());
        styleNew.setFillPattern(styleOld.getFillPattern());
        styleNew.setFont(this.transform(workbookNew,styleOld.getFont(workbookOld)));
        styleNew.setHidden(styleOld.getHidden());
        styleNew.setIndention(styleOld.getIndention());
        styleNew.setLocked(styleOld.getLocked());
        styleNew.setVerticalAlignment(styleOld.getVerticalAlignment());
        styleNew.setWrapText(styleOld.getWrapText());
        this.styleMap.put(hash, styleNew);
    }

private short transform(HSSFWorkbook workbookOld,XSSFWorkbook workbookNew,short index) {
    DataFormat formatOld = workbookOld.createDataFormat();
    DataFormat formatNew = workbookNew.createDataFormat();
    return formatNew.getFormat(formatOld.getFormat(index));
}


    private XSSFFont transform(XSSFWorkbook workbookNew,HSSFFont fontOld) {
        XSSFFont fontNew = workbookNew.createFont();
        fontNew.setBoldweight(fontOld.getBoldweight());
        fontNew.setCharSet(fontOld.getCharSet());
        fontNew.setColor(fontOld.getColor());
        fontNew.setFontName(fontOld.getFontName());
        fontNew.setFontHeight(fontOld.getFontHeight());
        fontNew.setItalic(fontOld.getItalic());
        fontNew.setStrikeout(fontOld.getStrikeout());
        fontNew.setTypeOffset(fontOld.getTypeOffset());
        fontNew.setUnderline(fontOld.getUnderline());
        return fontNew;
    }

public static void main(String[] args) throws Exception{
    Xls2Xlsx xls=new Xls2Xlsx(); 
    //xls.transform();
     InputStream isXls = new FileInputStream("c:/OTD1.xls");
     HSSFWorkbook workbookOld     = new HSSFWorkbook(isXls);

    String dest="c:/OTD.xlsx";

    FileOutputStream out = new FileOutputStream(dest);
    XSSFWorkbook workbookNew = new XSSFWorkbook();
    xls.transformHSSF( workbookOld , workbookNew) ;    
    workbookNew.write(out);

    out.close();

//    InputStream isXls = new FileInputStream("c:/OTD1.xls");
//    HSSFWorkbook workbookNew     = new HSSFWorkbook(isXls);



}
}

this code has been adapted from what I found here on coderanch forum

public final class ExcelDocumentConverter {
public static XSSFWorkbook convertWorkbookHSSFToXSSF(HSSFWorkbook source) {
    XSSFWorkbook retVal = new XSSFWorkbook();
    for (int i = 0; i < source.getNumberOfSheets(); i++) {
        XSSFSheet xssfSheet = retVal.createSheet();
        HSSFSheet hssfsheet = source.getSheetAt(i);
        copySheets(hssfsheet, xssfSheet);
    }
    return retVal;
}

public static void copySheets(HSSFSheet source, XSSFSheet destination) {
    copySheets(source, destination, true);
}

/**
 * @param destination
 *            the sheet to create from the copy.
 * @param the
 *            sheet to copy.
 * @param copyStyle
 *            true copy the style.
 */
public static void copySheets(HSSFSheet source, XSSFSheet destination, boolean copyStyle) {
    int maxColumnNum = 0;
    Map<Integer, HSSFCellStyle> styleMap = (copyStyle) ? new HashMap<Integer, HSSFCellStyle>() : null;
    for (int i = source.getFirstRowNum(); i <= source.getLastRowNum(); i++) {
        HSSFRow srcRow = source.getRow(i);
        XSSFRow destRow = destination.createRow(i);
        if (srcRow != null) {
            copyRow(source, destination, srcRow, destRow, styleMap);
            if (srcRow.getLastCellNum() > maxColumnNum) {
                maxColumnNum = srcRow.getLastCellNum();
            }
        }
    }
    for (int i = 0; i <= maxColumnNum; i++) {
        destination.setColumnWidth(i, source.getColumnWidth(i));
    }
}

/**
 * @param srcSheet
 *            the sheet to copy.
 * @param destSheet
 *            the sheet to create.
 * @param srcRow
 *            the row to copy.
 * @param destRow
 *            the row to create.
 * @param styleMap
 *            -
 */
public static void copyRow(HSSFSheet srcSheet, XSSFSheet destSheet, HSSFRow srcRow, XSSFRow destRow,
        Map<Integer, HSSFCellStyle> styleMap) {
    // manage a list of merged zone in order to not insert two times a
    // merged zone
    Set<CellRangeAddressWrapper> mergedRegions = new TreeSet<CellRangeAddressWrapper>();
    destRow.setHeight(srcRow.getHeight());
    // pour chaque row
    for (int j = srcRow.getFirstCellNum(); j <= srcRow.getLastCellNum(); j++) {
        HSSFCell oldCell = srcRow.getCell(j); // ancienne cell
        XSSFCell newCell = destRow.getCell(j); // new cell
        if (oldCell != null) {
            if (newCell == null) {
                newCell = destRow.createCell(j);
            }
            // copy chaque cell
            copyCell(oldCell, newCell, styleMap);
            // copy les informations de fusion entre les cellules
            // System.out.println("row num: " + srcRow.getRowNum() +
            // " , col: " + (short)oldCell.getColumnIndex());
            CellRangeAddress mergedRegion = getMergedRegion(srcSheet, srcRow.getRowNum(),
                    (short) oldCell.getColumnIndex());

            if (mergedRegion != null) {
                // System.out.println("Selected merged region: " +
                // mergedRegion.toString());
                CellRangeAddress newMergedRegion = new CellRangeAddress(mergedRegion.getFirstRow(),
                        mergedRegion.getLastRow(), mergedRegion.getFirstColumn(), mergedRegion.getLastColumn());
                // System.out.println("New merged region: " +
                // newMergedRegion.toString());
                CellRangeAddressWrapper wrapper = new CellRangeAddressWrapper(newMergedRegion);
                if (isNewMergedRegion(wrapper, mergedRegions)) {
                    mergedRegions.add(wrapper);
                    destSheet.addMergedRegion(wrapper.range);
                }
            }
        }
    }

}

/**
 * @param oldCell
 * @param newCell
 * @param styleMap
 */
public static void copyCell(HSSFCell oldCell, XSSFCell newCell, Map<Integer, HSSFCellStyle> styleMap) {
    if (styleMap != null) {
        int stHashCode = oldCell.getCellStyle().hashCode();
        HSSFCellStyle sourceCellStyle = styleMap.get(stHashCode);
        XSSFCellStyle destnCellStyle = newCell.getCellStyle();
        if (sourceCellStyle == null) {
            sourceCellStyle = oldCell.getSheet().getWorkbook().createCellStyle();
        }
        destnCellStyle.cloneStyleFrom(oldCell.getCellStyle());
        styleMap.put(stHashCode, sourceCellStyle);
        newCell.setCellStyle(destnCellStyle);
    }
    switch (oldCell.getCellType()) {
    case HSSFCell.CELL_TYPE_STRING:
        newCell.setCellValue(oldCell.getStringCellValue());
        break;
    case HSSFCell.CELL_TYPE_NUMERIC:
        newCell.setCellValue(oldCell.getNumericCellValue());
        break;
    case HSSFCell.CELL_TYPE_BLANK:
        newCell.setCellType(HSSFCell.CELL_TYPE_BLANK);
        break;
    case HSSFCell.CELL_TYPE_BOOLEAN:
        newCell.setCellValue(oldCell.getBooleanCellValue());
        break;
    case HSSFCell.CELL_TYPE_ERROR:
        newCell.setCellErrorValue(oldCell.getErrorCellValue());
        break;
    case HSSFCell.CELL_TYPE_FORMULA:
        newCell.setCellFormula(oldCell.getCellFormula());
        break;
    default:
        break;
    }

}

/**
 * Récupère les informations de fusion des cellules dans la sheet source
 * pour les appliquer à la sheet destination... Récupère toutes les zones
 * merged dans la sheet source et regarde pour chacune d'elle si elle se
 * trouve dans la current row que nous traitons. Si oui, retourne l'objet
 * CellRangeAddress.
 * 
 * @param sheet
 *            the sheet containing the data.
 * @param rowNum
 *            the num of the row to copy.
 * @param cellNum
 *            the num of the cell to copy.
 * @return the CellRangeAddress created.
 */
public static CellRangeAddress getMergedRegion(HSSFSheet sheet, int rowNum, short cellNum) {
    for (int i = 0; i < sheet.getNumMergedRegions(); i++) {
        CellRangeAddress merged = sheet.getMergedRegion(i);
        if (merged.isInRange(rowNum, cellNum)) {
            return merged;
        }
    }
    return null;
}

/**
 * Check that the merged region has been created in the destination sheet.
 * 
 * @param newMergedRegion
 *            the merged region to copy or not in the destination sheet.
 * @param mergedRegions
 *            the list containing all the merged region.
 * @return true if the merged region is already in the list or not.
 */
private static boolean isNewMergedRegion(CellRangeAddressWrapper newMergedRegion,
        Set<CellRangeAddressWrapper> mergedRegions) {
    return !mergedRegions.contains(newMergedRegion);
}
}

Since all of the above answers don't help, here is working code:

Just write a main method that fills the necessary fields and uses transform().

package myStuff;

import java.io.*;
import java.util.*;

import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xssf.usermodel.*;

public class ExcelConverter {

private File path = null;
private ArrayList<File> inputFiles = new ArrayList<File>();
private HSSFWorkbook workbookOld = null;
private XSSFWorkbook workbookNew = null;
private int lastColumn = 0;
private HashMap<Integer, XSSFCellStyle> styleMap = null;

private void getInputFiles() {
    String call = "getInputFiles ";
    if (this.path.isFile()) {
        if (this.path.getAbsolutePath().endsWith(".xls")
                && !new File(this.path.getAbsolutePath() + "x").exists())
            this.inputFiles.add(this.path);
        else {
            System.out
                    .println("Datei endet nicht mit .xls oder XLSX-Datei existiert bereits");
        }
    } else
        for (File f : this.path.listFiles(new FilenameFilter() {
            // anonyme innere Klasse

            @Override
            public boolean accept(File dir, String name) {
                if (name.endsWith(".xls"))
                    return true;
                return false;
            }

        })) {
            if (!new File(f.getAbsoluteFile() + "x").exists()) {
                this.inputFiles.add(f);
            }
        }
    System.out
            .println(call + "Dateien gefunden: " + this.inputFiles.size());
    System.out.println(call + "abgeschlossen");
}

private HSSFWorkbook getWorkBook(File f) throws FileNotFoundException,
        IOException {
    System.out.println("getWorkBook lese " + f.getAbsolutePath());
    POIFSFileSystem fs = new POIFSFileSystem(new BufferedInputStream(
            new FileInputStream(f)));
    HSSFWorkbook workbook = new HSSFWorkbook(fs);
    System.out.println("getWorkBook abgeschlossen");
    return workbook;
}

private void transform() {
    String call = "transform ";
    System.out.println(call + "Workbook");
    XSSFSheet sheetNew;
    HSSFSheet sheetOld;
    this.workbookNew.setForceFormulaRecalculation(this.workbookOld
            .getForceFormulaRecalculation());
    // workbookNew.setHidden(workbookOld.isHidden()); //[email protected] -
    // von Apache noch nicht implementiert
    this.workbookNew.setMissingCellPolicy(this.workbookOld
            .getMissingCellPolicy());

    for (int i = 0; i < this.workbookOld.getNumberOfSheets(); i++) {
        sheetOld = this.workbookOld.getSheetAt(i);
        sheetNew = this.workbookNew.getSheet(sheetOld.getSheetName());
        System.out.println(call + "Sheet erstellt: "
                + sheetOld.getSheetName());
        sheetNew = this.workbookNew.createSheet(sheetOld.getSheetName());
        this.transform(sheetOld, sheetNew);
    }
    System.out.println(call + "Anzahl verwendeter Styles: "
            + this.styleMap.size());
    System.out.println(call + "abgeschlossen");
}

private void transform(HSSFSheet sheetOld, XSSFSheet sheetNew) {
    System.out.println("transform Sheet");

    sheetNew.setDisplayFormulas(sheetOld.isDisplayFormulas());
    sheetNew.setDisplayGridlines(sheetOld.isDisplayGridlines());
    sheetNew.setDisplayGuts(sheetOld.getDisplayGuts());
    sheetNew.setDisplayRowColHeadings(sheetOld.isDisplayRowColHeadings());
    sheetNew.setDisplayZeros(sheetOld.isDisplayZeros());
    sheetNew.setFitToPage(sheetOld.getFitToPage());
    sheetNew.setForceFormulaRecalculation(sheetOld
            .getForceFormulaRecalculation());
    sheetNew.setHorizontallyCenter(sheetOld.getHorizontallyCenter());
    sheetNew.setMargin(Sheet.BottomMargin,
            sheetOld.getMargin(Sheet.BottomMargin));
    sheetNew.setMargin(Sheet.FooterMargin,
            sheetOld.getMargin(Sheet.FooterMargin));
    sheetNew.setMargin(Sheet.HeaderMargin,
            sheetOld.getMargin(Sheet.HeaderMargin));
    sheetNew.setMargin(Sheet.LeftMargin,
            sheetOld.getMargin(Sheet.LeftMargin));
    sheetNew.setMargin(Sheet.RightMargin,
            sheetOld.getMargin(Sheet.RightMargin));
    sheetNew.setMargin(Sheet.TopMargin, sheetOld.getMargin(Sheet.TopMargin));
    sheetNew.setPrintGridlines(sheetNew.isPrintGridlines());
    sheetNew.setRightToLeft(sheetNew.isRightToLeft());
    sheetNew.setRowSumsBelow(sheetNew.getRowSumsBelow());
    sheetNew.setRowSumsRight(sheetNew.getRowSumsRight());
    sheetNew.setVerticallyCenter(sheetOld.getVerticallyCenter());

    XSSFRow rowNew;
    for (Row row : sheetOld) {
        rowNew = sheetNew.createRow(row.getRowNum());
        if (rowNew != null)
            this.transform((HSSFRow) row, rowNew);
    }

    for (int i = 0; i < this.lastColumn; i++) {
        sheetNew.setColumnWidth(i, sheetOld.getColumnWidth(i));
        sheetNew.setColumnHidden(i, sheetOld.isColumnHidden(i));
    }

    for (int i = 0; i < sheetOld.getNumMergedRegions(); i++) {
        CellRangeAddress merged = sheetOld.getMergedRegion(i);
        sheetNew.addMergedRegion(merged);
    }
}

private void transform(HSSFRow rowOld, XSSFRow rowNew) {
    XSSFCell cellNew;
    rowNew.setHeight(rowOld.getHeight());
    if (rowOld.getRowStyle() != null) {
        Integer hash = rowOld.getRowStyle().hashCode();
        if (!this.styleMap.containsKey(hash))
            this.transform(hash, rowOld.getRowStyle(),
                    this.workbookNew.createCellStyle());
        rowNew.setRowStyle(this.styleMap.get(hash));
    }
    for (Cell cell : rowOld) {
        cellNew = rowNew.createCell(cell.getColumnIndex(),
                cell.getCellType());
        if (cellNew != null)
            this.transform((HSSFCell) cell, cellNew);
    }
    this.lastColumn = Math.max(this.lastColumn, rowOld.getLastCellNum());
}

private void transform(HSSFCell cellOld, XSSFCell cellNew) {
    cellNew.setCellComment(cellOld.getCellComment());

    Integer hash = cellOld.getCellStyle().hashCode();
    if (!this.styleMap.containsKey(hash)) {
        this.transform(hash, cellOld.getCellStyle(),
                this.workbookNew.createCellStyle());
    }
    cellNew.setCellStyle(this.styleMap.get(hash));

    switch (cellOld.getCellType()) {
    case Cell.CELL_TYPE_BLANK:
        break;
    case Cell.CELL_TYPE_BOOLEAN:
        cellNew.setCellValue(cellOld.getBooleanCellValue());
        break;
    case Cell.CELL_TYPE_ERROR:
        cellNew.setCellValue(cellOld.getErrorCellValue());
        break;
    case Cell.CELL_TYPE_FORMULA:
        cellNew.setCellValue(cellOld.getCellFormula());
        break;
    case Cell.CELL_TYPE_NUMERIC:
        cellNew.setCellValue(cellOld.getNumericCellValue());
        break;
    case Cell.CELL_TYPE_STRING:
        cellNew.setCellValue(cellOld.getStringCellValue());
        break;
    default:
        System.out.println("transform: Unbekannter Zellentyp "
                + cellOld.getCellType());
    }
}

private void transform(Integer hash, HSSFCellStyle styleOld,
        XSSFCellStyle styleNew) {
    styleNew.setAlignment(styleOld.getAlignment());
    styleNew.setBorderBottom(styleOld.getBorderBottom());
    styleNew.setBorderLeft(styleOld.getBorderLeft());
    styleNew.setBorderRight(styleOld.getBorderRight());
    styleNew.setBorderTop(styleOld.getBorderTop());
    styleNew.setDataFormat(this.transform(styleOld.getDataFormat()));
    styleNew.setFillBackgroundColor(styleOld.getFillBackgroundColor());
    styleNew.setFillForegroundColor(styleOld.getFillForegroundColor());
    styleNew.setFillPattern(styleOld.getFillPattern());
    styleNew.setFont(this.transform(styleOld.getFont(this.workbookOld)));
    styleNew.setHidden(styleOld.getHidden());
    styleNew.setIndention(styleOld.getIndention());
    styleNew.setLocked(styleOld.getLocked());
    styleNew.setVerticalAlignment(styleOld.getVerticalAlignment());
    styleNew.setWrapText(styleOld.getWrapText());
    this.styleMap.put(hash, styleNew);
}

private short transform(short index) {
    DataFormat formatOld = this.workbookOld.createDataFormat();
    DataFormat formatNew = this.workbookNew.createDataFormat();
    return formatNew.getFormat(formatOld.getFormat(index));
}

private XSSFFont transform(HSSFFont fontOld) {
    XSSFFont fontNew = this.workbookNew.createFont();
    fontNew.setBoldweight(fontOld.getBoldweight());
    fontNew.setCharSet(fontOld.getCharSet());
    fontNew.setColor(fontOld.getColor());
    fontNew.setFontName(fontOld.getFontName());
    fontNew.setFontHeight(fontOld.getFontHeight());
    fontNew.setItalic(fontOld.getItalic());
    fontNew.setStrikeout(fontOld.getStrikeout());
    fontNew.setTypeOffset(fontOld.getTypeOffset());
    fontNew.setUnderline(fontOld.getUnderline());
    return fontNew;
}
}