poi 取excel单元格内容时，需要判断单元格的类型，才能正确取出

以下内容非原创，原文链接http://blog.sina.com.cn/s/blog_4b5bc01101015iuq.html

ate String getCellValue(HSSFCell cell) {  
        String cellValue = "";  
        DecimalFormat df = new DecimalFormat("#");  
        switch (cell.getCellType()) {  
        case HSSFCell.CELL_TYPE_STRING:  
            cellValue = cell.getRichStringCellValue().getString().trim();  
            break;  
        case HSSFCell.CELL_TYPE_NUMERIC:  
            cellValue = df.format(cell.getNumericCellValue()).toString();  
            break;  
        case HSSFCell.CELL_TYPE_BOOLEAN:  
            cellValue = String.valueOf(cell.getBooleanCellValue()).trim();  
            break;  
        case HSSFCell.CELL_TYPE_FORMULA:  
            cellValue = cell.getCellFormula();  
            break;  
        default:  
            cellValue = "";  
        }  
        return cellValue;  
    }