範例 - JavaScript 等比例縮小圖片

max-width、max-height以及這兩個的 min 版本是偶爾能在某些CSS中看到的屬性設定
不過因為IE不會辨識這些屬性，所以就直接寫JavaScript 調整圖片大小

var img = this.getElementsByTagName("img")[0];

img.onload = function(){
    var maxWidth = "300", maxHeight = "80";
 
    if(img.offsetHeight >= (maxHeight / maxWidth) * img.offsetWidth){
    img.style.width = img.offsetWidth / img.offsetHeight * maxHeight + "px";
    img.style.height = maxHeight + "px";
    }else{
img.style.height = img.offsetHeight / img.offsetWidth * maxHeight + "px";
img.style.width = maxWidth + "px";
    }
}

POI 自訂方法

copyRow() - 複製Row的method
updateFormula() - 計算Excel公式結果的方法

複製Row的method

POI有cloneSheet()這個複製sheet的方便方法
但是卻缺少複製sheet裡的row的方法
當然考量到公式的計算與合併的儲存格的位置
這個方法須自訂是不太令人意外

private void copyRow(HSSFSheet worksheet, int sourceRowNum, int destinationRowNum) {

    // Get the source & new row

    HSSFRow newRow = worksheet.getRow(destinationRowNum);

    HSSFRow sourceRow = worksheet.getRow(sourceRowNum);

    // If the row exist in destination, push down all rows by 1 else create a new row

    if (newRow != null) {

        worksheet.shiftRows(destinationRowNum, worksheet.getLastRowNum(), 1);

    } else {

        newRow = worksheet.createRow(destinationRowNum);

    }

    // Loop through source columns to add to new row

    for (int i = 0; i < sourceRow.getLastCellNum(); i++) {

        // Grab a copy of the old/new cell

        HSSFCell oldCell = sourceRow.getCell(i);

        HSSFCell newCell = newRow.createCell(i);

        // If the old cell is null jump to next cell

        if (oldCell == null) {

            newCell = null;

            continue;

        }

        // Use old cell style

        newCell.setCellStyle(oldCell.getCellStyle());

        // If there is a cell comment, copy

        if (newCell.getCellComment() != null) {

            newCell.setCellComment(oldCell.getCellComment());

        }

        // If there is a cell hyperlink, copy

        if (oldCell.getHyperlink() != null) {

            newCell.setHyperlink(oldCell.getHyperlink());

        }

        // Set the cell data type

        newCell.setCellType(oldCell.getCellType());

        // Set the cell data value

        switch (oldCell.getCellType()) {

            case Cell.CELL_TYPE_BLANK:

                newCell.setCellValue(oldCell.getStringCellValue());

                break;

            case Cell.CELL_TYPE_BOOLEAN:

                newCell.setCellValue(oldCell.getBooleanCellValue());

                break;

            case Cell.CELL_TYPE_ERROR:

                newCell.setCellErrorValue(oldCell.getErrorCellValue());

                break;

            case Cell.CELL_TYPE_FORMULA:

                newCell.setCellFormula(oldCell.getCellFormula());

                break;

            case Cell.CELL_TYPE_NUMERIC:

                newCell.setCellValue(oldCell.getNumericCellValue());

                break;

            case Cell.CELL_TYPE_STRING:

                newCell.setCellValue(oldCell.getRichStringCellValue());

                break;

        }

    }

    // If there are are any merged regions in the source row, copy to new row

    for (int i = 0; i < worksheet.getNumMergedRegions(); i++) {

        CellRangeAddress cellRangeAddress = worksheet.getMergedRegion(i);

        if (cellRangeAddress.getFirstRow() == sourceRow.getRowNum()) {

            CellRangeAddress newCellRangeAddress =
                  new CellRangeAddress(newRow.getRowNum(),

                    (newRow.getRowNum() +
                    (cellRangeAddress.getLastRow() - cellRangeAddress.getFirstRow())
                     ),

                    cellRangeAddress.getFirstColumn(),

                    cellRangeAddress.getLastColumn());

            worksheet.addMergedRegion(newCellRangeAddress);

        }

    }

}


計算Excel公式結果的方法

使用POI填入公式時，Excel表並不會將計算後的結果立刻展示
它的作法是顯示出公式(舊版office)或待開啟編輯權限後才計算(office 2010)
以下方法能計算特定行數的Excel公式


private void updateFormula(HSSFWorkbook wb, HSSFSheet sheet, int row){    
    Row r = sheet.getRow(row);    
    Cell cell = null;    
    HSSFFormulaEvaluator eval = new HSSFFormulaEvaluator(wb);    
    for(int i = r.getFirstCellNum(); i < r.getLastCellNum(); i++){    
        cell = r.getCell(i);    
        if(cell.getCellType()== Cell.CELL_TYPE_FORMULA)    
            eval.evaluateFormulaCell(cell);    
    }    
}


HSSFFormulaEvaluator提供了evaluateFormulaCell(Cell cell)方法
計算公式保存結果，但不改變公式
而evaluateInCell(Cell cell)方法是計算公式，並將原公式替換為計算結果，
也就是說該單元格的類型從Cell.CELL_TYPE_FORMULA改為Cell.CELL_TYPE_NUMBERIC

HSSFFormulaEvaluator提供了靜態方法evaluateAllFormulaCells(HSSFWorkbook wb)
計算一個Excel文件的所有公式，用起來很方便

範例 - 刪除目錄及其底下所有文件

      public void deleteAll(File path){
          if(path.exists()){
              if(path.isFile()){ 
                  path.delete(); 
              }else{ 
                  File[] files = path.listFiles();     
                  for(int i = 0; i < files.length; i++){ 
                        deleteAll(files[i]); 
                  }
 
                  path.delete(); 
              }
          }
      }

範例 - 計算硬碟中的資料大小

int uAppendSize = 0;                                     //store uploaded data size info
                                     
File[] fList =TargetDir.listFiles();

for (int j = 0; j < fList.length; j++){
      FileInputStream in = new FileInputStream(fList[j]);
      uAppendSize += in.available();
      in.close();         //must close FileInputStream after use it
}

這個範例會檢查寫入檔案所在的資料夾，並加該資料夾內的所有檔案大小相加
FileInputStream 開啟後務必要記得關閉
否則檔案的刪除、修改等動作會因為檔案被FileInputStream佔用而失敗

自訂編碼標籤範例

如果不將Eclipse的環境編碼改成UTF-8，似乎轉碼會有問題
因應這種情況寫了自訂標籤來協助處理

encrypt.tld=========

<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
    version="2.0">

    <tlib-version>1.2</tlib-version>            
    <short-name>encryptlib</short-name>    
    <uri>encrypt-tags</uri>                              
    <tag>
      <description>URL  get/post encrypting</description>
      <name>encrypt</name>
      <tag-class>tw.vencs.EncrptTag</tag-class>
      <body-content>empty</body-content>
    
      <attribute>
          <name>encryptValue</name>
          <required>true</required>
          <rtexprvalue>true</rtexprvalue>
      </attribute>
    </tag>

</taglib>

EncrptTag.java===============

package tw.vencs;

import javax.servlet.jsp.tagext.SimpleTagSupport;
import javax.servlet.jsp.JspException;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;

public class EncrptTag extends SimpleTagSupport{
    private String encryptValue; 
   
    public void doTag() throws JspException { 
        try { 
            encryptValue = new String(encryptValue.getBytes("iso-8859-1"),"UTF-8"); 
            getJspContext().getOut().write(encryptValue);
        } catch (IOException e) { 
              Logger.getLogger(EncrptTag.class.getName()).log(Level.SEVERE, null, e);
              throw new RuntimeException();
        }    
    } 
    public void setEncryptValue(String encryptValue) { 
        this.encryptValue = encryptValue; 
    } 
}

Demo.jsp===============

.....
<%@ taglib prefix="e" uri="encrypt-tags" %>
.....
<body>
.....
....=<e:encrypt  encryptValue="${param.itemName}"/>
</body>
.....