displaytag的Excel导出实践

前言
  Displaytag官网有 1.0, 1.1, 1.2等，注意找到对应的版本。源码和API可以在Maven库中找到。
  常规的使用不是问题，这里说说关于Excel导出的问题，中文乱码，使用POI等。我使用的是Displaytag1.1。

基本导出功能
  这种情况只需引入displaytag-1.1.jar。
  设置column属性media="html"将不会导出，media="excel"不会页面显示，默认既显示又导出。
  setProperty也可以写在displaytag.properties中应用于所有表格。

online demo

  <display:table name="test" export="true" id="currentRowObject">
    <display:column property="id" title="ID" />
    <display:column property="email" />
    <display:column property="status" />
    <display:column media="html" property="date" />
    <display:setProperty name="export.excel" value="true" />
    <display:setProperty name="export.excel.filename" value="export.xls" />
  </display:table>

  这时候导出的excel打开的时候office会报警，但是能够打开，因为这不是正真的excel，只是csv改了后缀的纯文本格式。可能出现中文乱码，通过重载ExcelView来解决。

Class SimpleChineseExcelView extends ExcelView {
  public String getMimeType(){
    //原代码是return "application/vnd.ms-excel";
    return "application/vnd.ms-excel;charset=gbk"; 
  }
}

  修改displaytag.properties中对应条目：
  export.excel.class=yourpackage.SimpleChineseExcelView
 
  这样就勉强能用了，只要能够忍受每次都需要另存为excel来避免报警，不用中文文件名，不在bodycontent中使用中文。这样的实现只能是差强人意。 中文问题解决


使用POI
  需要引入额外的displaytag-export-excel-1.1.jar，使用Maven解决依赖。
  修改displaytag.properties中对应条目：
  export.excel.class=org.displaytag.export.excel.ExcelHssfView
  配置export filter：

<!--Configure the Filter in your web.xml:-->
  <filter>
    <filter-name>ResponseOverrideFilter</filter-name>
    <filter-class>org.displaytag.filter.ResponseOverrideFilter</filter-class>
  </filter>
<!--And add mappings for urls the filter will intercept, for example:-->
  <filter-mapping>
    <filter-name>ResponseOverrideFilter</filter-name>
    <url-pattern>*.do</url-pattern>
  </filter-mapping>
  <filter-mapping>
    <filter-name>ResponseOverrideFilter</filter-name>
    <url-pattern>*.jsp</url-pattern>
  </filter-mapping>

  filter-mapping加在struts之前，acegi之后（如果有），放struts之后会出问题。
  很好地解决各种中文问题，也是真正的excel。

  实践Hack：
  项目中已经有了 poi3.6，而displaytag-export-excel-1.1依赖的是 poi3.0，版本太高，需要重新写一个ExcelHssfView。其实很简单，找到ExcelHssfView的源码，删除其中的所有的setEncoding方法，setEncoding方法在poi3.6中没有。修改后的代码如下，当然记得修改export.excel.class：

package com.lingceng;

import java.io.OutputStream;
import java.util.Calendar;
import java.util.Date;
import java.util.Iterator;

import javax.servlet.jsp.JspException;

import org.apache.commons.lang.ObjectUtils;
import org.apache.commons.lang.StringEscapeUtils;
import org.apache.commons.lang.StringUtils;
import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFCellStyle;
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.displaytag.Messages;
import org.displaytag.exception.BaseNestableJspTagException;
import org.displaytag.exception.SeverityEnum;
import org.displaytag.export.BinaryExportView;
import org.displaytag.model.Column;
import org.displaytag.model.ColumnIterator;
import org.displaytag.model.HeaderCell;
import org.displaytag.model.Row;
import org.displaytag.model.RowIterator;
import org.displaytag.model.TableModel;


/**
 * Excel exporter using POI HSSF.
 * @author Fabrizio Giustina
 * @author rapruitt
 * @version $Revision: 1.2 $ ($Author: fgiust $)
 */
public class MyExcelHssfView implements BinaryExportView
{

    /**
     * TableModel to render.
     */
    private TableModel model;

    /**
     * export full list?
     */
    private boolean exportFull;

    /**
     * include header in export?
     */
    private boolean header;

    /**
     * decorate export?
     */
    private boolean decorated;

    /**
     * Generated sheet.
     */
    private HSSFSheet sheet;

    /**
     * @see org.displaytag.export.ExportView#setParameters(TableModel, boolean, boolean, boolean)
     */
    public void setParameters(TableModel tableModel, boolean exportFullList, boolean includeHeader,
        boolean decorateValues)
    {
        this.model = tableModel;
        this.exportFull = exportFullList;
        this.header = includeHeader;
        this.decorated = decorateValues;
    }

    /**
     * @return "application/vnd.ms-excel"
     * @see org.displaytag.export.BaseExportView#getMimeType()
     */
    public String getMimeType()
    {
        return "application/vnd.ms-excel"; //$NON-NLS-1$
    }

    /**
     * @see org.displaytag.export.BinaryExportView#doExport(OutputStream)
     */
    public void doExport(OutputStream out) throws JspException
    {
        try
        {
            HSSFWorkbook wb = new HSSFWorkbook();
            sheet = wb.createSheet("-");

            int rowNum = 0;
            int colNum = 0;

            if (this.header)
            {
                // Create an header row
                HSSFRow xlsRow = sheet.createRow(rowNum++);

                HSSFCellStyle headerStyle = wb.createCellStyle();
                headerStyle.setFillPattern(HSSFCellStyle.FINE_DOTS);
                headerStyle.setFillBackgroundColor(HSSFColor.BLUE_GREY.index);
                HSSFFont bold = wb.createFont();
                bold.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);
                bold.setColor(HSSFColor.WHITE.index);
                headerStyle.setFont(bold);

                Iterator iterator = this.model.getHeaderCellList().iterator();

                while (iterator.hasNext())
                {
                    HeaderCell headerCell = (HeaderCell) iterator.next();

                    String columnHeader = headerCell.getTitle();

                    if (columnHeader == null)
                    {
                        columnHeader = StringUtils.capitalize(headerCell.getBeanPropertyName());
                    }

                    HSSFCell cell = xlsRow.createCell((short) colNum++);
                    cell.setCellValue(columnHeader);
                    cell.setCellStyle(headerStyle);
                    //cell.setEncoding(HSSFCell.ENCODING_UTF_16);
                }
            }

            // get the correct iterator (full or partial list according to the exportFull field)
            RowIterator rowIterator = this.model.getRowIterator(this.exportFull);
            // iterator on rows

            while (rowIterator.hasNext())
            {
                Row row = rowIterator.next();
                HSSFRow xlsRow = sheet.createRow(rowNum++);
                colNum = 0;

                // iterator on columns
                ColumnIterator columnIterator = row.getColumnIterator(this.model.getHeaderCellList());

                while (columnIterator.hasNext())
                {
                    Column column = columnIterator.nextColumn();

                    // Get the value to be displayed for the column
                    Object value = column.getValue(this.decorated);

                    HSSFCell cell = xlsRow.createCell((short) colNum++);
                    //cell.setEncoding(HSSFCell.ENCODING_UTF_16);

                    if (value instanceof Number)
                    {
                        Number num = (Number) value;
                        cell.setCellValue(num.doubleValue());
                    }
                    else if (value instanceof Date)
                    {
                        cell.setCellValue((Date) value);
                    }
                    else if (value instanceof Calendar)
                    {
                        cell.setCellValue((Calendar) value);
                    }
                    else
                    {
                        cell.setCellValue(escapeColumnValue(value));
                    }

                }
            }
            wb.write(out);
        }
        catch (Exception e)
        {
            throw new ExcelGenerationException(e);
        }
    }

    // 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;
    }

    /**
     * Wraps IText-generated exceptions.
     * @author Fabrizio Giustina
     * @version $Revision: 1.2 $ ($Author: fgiust $)
     */
    static class ExcelGenerationException 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 ExcelGenerationException(Throwable cause)
        {
            super(ExcelHssfView.class, Messages.getString("ExcelView.errorexporting"), cause); //$NON-NLS-1$
        }

        /**
         * @see org.displaytag.exception.BaseNestableJspTagException#getSeverity()
         */
        public SeverityEnum getSeverity()
        {
            return SeverityEnum.ERROR;
        }
    }

}