Index: src/main/java/org/displaytag/decorator/hssf/DecoratesHssf.java
===================================================================
RCS file: src/main/java/org/displaytag/decorator/hssf/DecoratesHssf.java
diff -N src/main/java/org/displaytag/decorator/hssf/DecoratesHssf.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ src/main/java/org/displaytag/decorator/hssf/DecoratesHssf.java	1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,31 @@
+/**
+ * Licensed under the Artistic License; you may not use this file
+ * except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://displaytag.sourceforge.net/license.html
+ *
+ * THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+package org.displaytag.decorator.hssf;
+
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+
+/**
+ * An implementor of this interface decorates tables and columns appearing in an HSSF workbook.
+ * 
+ * @author Jorge L. Barroso
+ * @version $Revision:     $ ($Author: jbarroso $)
+ */
+public interface DecoratesHssf
+{
+    /**
+     * Set the worksheet used to render a table model.
+     * 
+     * @param sheet The worksheet used to render a table model.
+     */
+    void setSheet(HSSFSheet sheet);
+}
Index: src/main/java/org/displaytag/export/excel/DefaultHssfExportView.java
===================================================================
RCS file: src/main/java/org/displaytag/export/excel/DefaultHssfExportView.java
diff -N src/main/java/org/displaytag/export/excel/DefaultHssfExportView.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ src/main/java/org/displaytag/export/excel/DefaultHssfExportView.java	1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,105 @@
+/**
+ * Licensed under the Artistic License; you may not use this file
+ * except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://displaytag.sourceforge.net/license.html
+ *
+ * THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+package org.displaytag.export.excel;
+
+import java.io.IOException;
+import java.io.OutputStream;
+
+import javax.servlet.jsp.JspException;
+
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.displaytag.Messages;
+import org.displaytag.exception.BaseNestableJspTagException;
+import org.displaytag.exception.SeverityEnum;
+import org.displaytag.export.BinaryExportView;
+import org.displaytag.model.TableModel;
+import org.displaytag.render.HssfTableWriter;
+
+/**
+ * Excel exporter using POI.
+ * 
+ * @author Jorge L. Barroso
+ * @version $Revision:     $ ($Author: jbarroso $)
+ */
+public class DefaultHssfExportView implements BinaryExportView
+{
+    /**
+     * TableModel to render.
+     */
+    private TableModel model;
+    
+    /**
+     * @see org.displaytag.export.BinaryExportView#doExport(java.io.OutputStream)
+     */
+    public void doExport(OutputStream out) throws IOException, JspException
+    {
+        try
+        {
+            HSSFWorkbook wb = new HSSFWorkbook();
+            new HssfTableWriter(wb).writeTable(this.model, "-1");
+            wb.write(out);
+        }
+        catch (Exception e)
+        {
+            throw new HssfGenerationException(e);
+        }
+    }
+
+    /** 
+     * @see org.displaytag.export.ExportView#setParameters(org.displaytag.model.TableModel, boolean, boolean, boolean)
+     */
+    public void setParameters(TableModel model, boolean exportFullList,
+            boolean includeHeader, boolean decorateValues)
+    {
+        this.model = model;
+    }
+
+    /**
+     * @see org.displaytag.export.BaseExportView#getMimeType()
+     * @return "application/vnd.ms-excel"
+     */
+    public String getMimeType()
+    {
+        return "application/vnd.ms-excel"; //$NON-NLS-1$
+    }
+    
+    /**
+     * Wraps POI-generated exceptions.
+     * @author Fabrizio Giustina
+     * @version $Revision: 1.3 $ ($Author: jbarroso $)
+     */
+    static class HssfGenerationException extends BaseNestableJspTagException
+    {
+        /**
+         * D1597A17A6.
+         */
+        private static final long serialVersionUID = 899149338534L;
+
+        /**
+         * Instantiate a new PdfGenerationException with a fixed message and the given cause.
+         * @param cause Previous exception
+         */
+        public HssfGenerationException(Throwable cause)
+        {
+            super(DefaultHssfExportView.class, Messages.getString("DefaultHssfExportView.errorexporting"), cause); //$NON-NLS-1$
+        }
+
+        /**
+         * @see org.displaytag.exception.BaseNestableJspTagException#getSeverity()
+         */
+        public SeverityEnum getSeverity()
+        {
+            return SeverityEnum.ERROR;
+        }
+    }
+}
Index: src/main/java/org/displaytag/render/HssfTableWriter.java
===================================================================
RCS file: src/main/java/org/displaytag/render/HssfTableWriter.java
diff -N src/main/java/org/displaytag/render/HssfTableWriter.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ src/main/java/org/displaytag/render/HssfTableWriter.java	1 Jan 1970 00:00:00 -0000
@@ -0,0 +1,386 @@
+/**
+ * Licensed under the Artistic License; you may not use this file
+ * except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://displaytag.sourceforge.net/license.html
+ *
+ * THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+package org.displaytag.render;
+
+import java.util.Calendar;
+import java.util.Date;
+import java.util.Iterator;
+
+import org.apache.commons.beanutils.Converter;
+import org.apache.commons.lang.ObjectUtils;
+import org.apache.commons.lang.StringEscapeUtils;
+import org.apache.commons.lang.StringUtils;
+import org.apache.commons.lang.math.NumberUtils;
+import org.apache.poi.hssf.usermodel.HSSFCell;
+import org.apache.poi.hssf.usermodel.HSSFCellStyle;
+import org.apache.poi.hssf.usermodel.HSSFDataFormat;
+import org.apache.poi.hssf.usermodel.HSSFFont;
+import org.apache.poi.hssf.usermodel.HSSFRow;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.hssf.util.HSSFColor;
+import org.apache.poi.hssf.util.Region;
+import org.displaytag.conversion.PropertyConvertorFactory;
+import org.displaytag.decorator.TableDecorator;
+import org.displaytag.decorator.hssf.DecoratesHssf;
+import org.displaytag.model.Column;
+import org.displaytag.model.HeaderCell;
+import org.displaytag.model.Row;
+import org.displaytag.model.TableModel;
+import org.displaytag.properties.TableProperties;
+
+/**
+ * A table writer that formats a table in Excel's spreadsheet format,
+ * and writes it to an HSSF workbook.
+ * 
+ * @author Jorge L. Barroso
+ * @version $Revision:     $ ($Author: jbarroso $)
+ * @see org.displaytag.render.TableWriterTemplate
+ */
+public class HssfTableWriter extends TableWriterAdapter
+{
+    /**
+     * The workbook to which the table is written.
+     */
+    private HSSFWorkbook wb;
+    
+    /**
+     * Generated sheet.
+     */
+    private HSSFSheet sheet;
+    
+    /**
+     * Current row number.
+     */
+    private int rowNum;
+    
+    /**
+     * Current row.
+     */
+    private HSSFRow currentRow;
+
+    /**
+     * Current column number.
+     */
+    private int colNum;
+
+    /**
+     * Current cell.
+     */
+    private HSSFCell currentCell;
+    
+    /**
+     * Converter for producing numeric cell values.
+     */
+    private Converter propertyConvertor;
+
+    /**
+     * Percent Excel format.
+     */
+    private short pctFormat = HSSFDataFormat.getBuiltinFormat("0.00%");
+    
+    /**
+     * This table writer uses an HSSF workbook to write the table.
+     * @param wb The HSSF workbook to write the table.
+     */
+    public HssfTableWriter(HSSFWorkbook wb)
+    {
+        this.wb = wb;
+    }
+    
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeTableOpener(org.displaytag.model.TableModel)
+     */
+    protected void writeTableOpener(TableModel model) throws Exception
+    {
+        this.sheet             = wb.createSheet("-");
+        this.rowNum            = 0;
+        this.propertyConvertor = PropertyConvertorFactory.createNumberConverter(TableProperties.getInstance(null));
+    }
+
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeCaption(org.displaytag.model.TableModel)
+     */
+    protected void writeCaption(TableModel model) throws Exception
+    {
+        HSSFCellStyle style = this.wb.createCellStyle();
+        HSSFFont bold = this.wb.createFont();
+        bold.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);
+        bold.setFontHeightInPoints((short) 14);
+        style.setFont(bold);
+        style.setAlignment(HSSFCellStyle.ALIGN_CENTER);
+        
+        this.colNum = 0;
+        this.currentRow = this.sheet.createRow(this.rowNum++);
+        this.currentCell = this.currentRow.createCell((short) this.colNum);
+        this.currentCell.setCellStyle(style);
+        String caption = model.getCaption();
+        this.currentCell.setCellValue(caption);
+        this.rowSpanTable(model);
+    }
+
+    /**
+     * Obtain the region over which to merge a cell.
+     * 
+     * @param first Column number of first cell from which to merge.
+     * @param last Column number of last cell over which to merge.
+     * @return The region over which to merge a cell.
+     */
+    private Region getMergeCellsRegion(short first, short last)
+    {
+         return new Region(this.currentRow.getRowNum(), first, this.currentRow.getRowNum(), last);
+    }
+
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeTableHeader(org.displaytag.model.TableModel)
+     */
+    protected void writeTableHeader(TableModel model) throws Exception
+    {
+        this.currentRow = this.sheet.createRow(this.rowNum++);
+        this.colNum = 0;
+        HSSFCellStyle headerStyle = this.getHeaderFooterStyle();
+        for (Iterator iterator = model.getHeaderCellList().iterator(); iterator.hasNext();)
+        {
+            HeaderCell headerCell = (HeaderCell) iterator.next();
+            String columnHeader = headerCell.getTitle();
+            if (columnHeader == null)
+            {
+                columnHeader = StringUtils.capitalize(headerCell.getBeanPropertyName());
+            }
+
+            this.writeHeaderFooter(columnHeader, this.currentRow, headerStyle);
+        }
+    }
+
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeDecoratedRowStart(org.displaytag.model.TableModel)
+     */
+    protected void writeDecoratedRowStart(TableModel model)
+    {
+         model.getTableDecorator().startRow();
+    }
+
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeRowOpener(org.displaytag.model.TableModel)
+     */
+    protected void writeRowOpener(Row row) throws Exception
+    {
+         this.currentRow = this.sheet.createRow(rowNum++);
+         this.colNum = 0;
+    }
+
+    /**
+     * Write a column's opening structure to a HSSF document.
+     * @see org.displaytag.render.TableWriterTemplate#writeColumnOpener(org.displaytag.model.Column)
+     */
+    protected void writeColumnOpener(Column column) throws Exception
+    {
+        column.getOpenTag(); // has side effect, setting its stringValue, which affects grouping logic.
+        this.currentCell = this.currentRow.createCell((short) this.colNum++);
+        this.currentCell.setEncoding(HSSFCell.ENCODING_UTF_16);
+    }
+
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeColumnValue(java.lang.String,org.displaytag.model.Column)
+     */
+    protected void writeColumnValue(String val, Column column) throws Exception
+    {
+        Object value = (val == null) ? "" : val;
+        Class valueClass = column.getHeaderCell().getColumnValueClass();
+        if (valueClass != null)
+        {
+            value = this.propertyConvertor.convert(valueClass, value);
+            if (Number.class.isAssignableFrom(valueClass))
+            {
+                if (value.toString().indexOf("%") > -1)
+                {
+                    this.currentCell.setCellValue(((Number) value).doubleValue() / 100);
+                    HSSFCellStyle cellStyle = wb.createCellStyle();
+                    cellStyle.setDataFormat(pctFormat);
+                    this.currentCell.setCellStyle(cellStyle);
+                }
+                else
+                {
+                    this.currentCell.setCellValue(((Number) value).doubleValue());
+                }
+            }
+            else if (Date.class.isAssignableFrom(valueClass))
+            {
+                this.currentCell.setCellValue((Date) value);
+            }
+            else if (Calendar.class.isAssignableFrom(valueClass))
+            {
+                this.currentCell.setCellValue((Calendar) value);
+            }
+            else
+            {
+                this.currentCell.setCellValue(this.escapeColumnValue(value));
+            }
+        }
+        else
+        {
+            if (this.isNumber(value.toString()))
+            {
+                Number num = (Number) this.propertyConvertor.convert(Number.class, value.toString());
+                // Percentage
+                if (value.toString().indexOf("%") > -1)
+                {
+                    this.currentCell.setCellValue(num.doubleValue() / 100);
+                    HSSFCellStyle cellStyle = this.wb.createCellStyle();
+                    cellStyle.setDataFormat(this.pctFormat);
+                    this.currentCell.setCellStyle(cellStyle);
+                }
+                else
+                {
+                    this.currentCell.setCellValue(num.doubleValue());
+                }
+            }
+            else if (value instanceof Date)
+            {
+                this.currentCell.setCellValue((Date) value);
+            }
+            else if (value instanceof Calendar)
+            {
+                this.currentCell.setCellValue((Calendar) value);
+            }
+            else
+            {
+                this.currentCell.setCellValue(this.escapeColumnValue(value));
+            }
+        }
+    }
+    
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeDecoratedRowFinish(org.displaytag.model.TableModel)
+     */
+    protected void writeDecoratedRowFinish(TableModel model) throws Exception
+    {
+        DecoratesHssf decorator = (DecoratesHssf) model.getTableDecorator();
+        decorator.setSheet(this.sheet);
+        ((TableDecorator) decorator).finishRow();
+        this.rowNum = this.sheet.getLastRowNum();
+        this.rowNum++;
+    }
+    
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writePostBodyFooter(org.displaytag.model.TableModel)
+     */
+    protected void writePostBodyFooter(TableModel model) throws Exception
+    {
+        this.colNum = 0;
+        this.currentRow = this.sheet.createRow(this.rowNum++);
+        this.writeHeaderFooter(model.getFooter(), this.currentRow,
+                               this.getHeaderFooterStyle());
+        this.rowSpanTable(model);
+    }
+    
+    /**
+     * Make a row span the width of the table.
+     * 
+     * @param model The table model representing the rendered table.
+     */
+    private void rowSpanTable(TableModel model)
+    {
+        this.sheet.addMergedRegion(this.getMergeCellsRegion(this.currentCell.getCellNum(),
+                                                           (short) (model.getNumberOfColumns() - 1)));
+    }
+
+    /**
+     * @see org.displaytag.render.TableWriterTemplate#writeDecoratedTableFinish(org.displaytag.model.TableModel)
+     */
+    protected void writeDecoratedTableFinish(TableModel model)
+    {
+        model.getTableDecorator().finish();
+    }
+
+    // patch from Karsten Voges
+    /**
+     * Escape certain values that are not permitted in excel cells.
+     * @param rawValue the object value
+     * @return the escaped value
+     */
+    protected String escapeColumnValue(Object rawValue)
+    {
+        if (rawValue == null)
+        {
+            return null;
+        }
+        String returnString = ObjectUtils.toString(rawValue);
+        // escape the String to get the tabs, returns, newline explicit as \t \r \n
+        returnString = StringEscapeUtils.escapeJava(StringUtils.trimToEmpty(returnString));
+        // remove tabs, insert four whitespaces instead
+        returnString = StringUtils.replace(StringUtils.trim(returnString), "\\t", "    ");
+        // remove the return, only newline valid in excel
+        returnString = StringUtils.replace(StringUtils.trim(returnString), "\\r", " ");
+        // unescape so that \n gets back to newline
+        returnString = StringEscapeUtils.unescapeJava(returnString);
+        return returnString;
+    }
+
+    /**
+     * Is this value numeric? You should probably override this method to handle your locale.
+     * @param rawValue the object value
+     * @return true if numeric
+     */
+    protected boolean isNumber(String rawValue)
+    {
+        if (rawValue == null)
+        {
+            return false;
+        }
+        String rawV = rawValue;
+        if (rawV.indexOf('%') > -1)
+        {
+            rawV = rawV.replace('%', ' ').trim();
+        }
+        if (rawV.indexOf('$') > -1)
+        {
+            rawV = rawV.replace('$', ' ').trim();
+        }
+        if (rawV.indexOf(',') > -1)
+        {
+            rawV = StringUtils.replace(rawV, ",", "");
+        }
+        return NumberUtils.isNumber(rawV.trim());
+    }
+    
+    /**
+     * Writes a table header or a footer.
+     * 
+     * @param value Header or footer value to be rendered.
+     * @param row The row in which to write the header or footer.
+     * @param style Style used to render the header or footer.
+     */
+    private void writeHeaderFooter(String value, HSSFRow row, HSSFCellStyle style)
+    {
+        this.currentCell = row.createCell((short) this.colNum++);
+        this.currentCell.setCellValue(value);
+        this.currentCell.setCellStyle(style);
+        this.currentCell.setEncoding(HSSFCell.ENCODING_UTF_16);
+    }
+    
+    /**
+     * Obtain the style used to render a header or footer.
+     * @return The style used to render a header or footer.
+     */
+    private HSSFCellStyle getHeaderFooterStyle()
+    {
+        HSSFCellStyle style = this.wb.createCellStyle();
+        style.setFillPattern(HSSFCellStyle.FINE_DOTS);
+        style.setFillBackgroundColor(HSSFColor.BLUE_GREY.index);
+        HSSFFont bold = this.wb.createFont();
+        bold.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);
+        bold.setColor(HSSFColor.WHITE.index);
+        style.setFont(bold);
+        return style;
+    }
+}