灵活使用递归算法，生成Excel文件中的复合表头

    最近，在开发中，需要导出数据到excel文件，文件的表头的格式是不一致的。有复合表头，也有单表头，那么如何灵活地生成excel文件中的复合表头。



首先有一个JSON字符串格式的字段描述,如下所示:
       var columnDefs = [{
                key:"unit",
                label:"单位"
            },{
                key:"form",
                label:"货物"
            },{
                key:"putin",
                label:"2011年03月",
                children:[{
                        key:"shout",
                        label:"buy"
                },{
                        key:"sale",
                        label:"销售"
                },{
                        key:"rate",
                        label:"百分比(%)"
                }]
            },{
                key:"average",
                label:"平均(%)"
            }];
 
    如果表的宾栏中有子栏，children是不为空的。自己写的代码，是在项目中写的，比较匆忙，还有提高的余地：

  

   private int insertHeader(HSSFSheet sheet, List columns, 
                 int rowIndex, HSSFWorkbook wb) {
        HSSFCellStyle cellStyle = this.getCellStyle(wb);
        cellStyle.setAlignment(HSSFCellStyle.VERTICAL_CENTER);
        cellStyle.setAlignment(HSSFCellStyle.ALIGN_CENTER);
        HSSFRow row = sheet.createRow(rowIndex);
        //横向的单元格的列数,这里设置一个方法外的变量，初始化为零
        nextCellIndex  = 0;
        int rowNumber = setSubCellValue(sheet, rowIndex, 
                             cellStyle, row, nextCellIndex, columns);
        //设置每一行的自适应单元格内容的长度
        setColumnWidth(sheet, rowNumber);
        //返回生成表头之后的行数
        return rowNumber;
    }
    private int setSubCellValue(HSSFSheet sheet, 
            int rowIndex,    HSSFCellStyle cellStyle, 
            HSSFRow row, int nextCellIndex, List columns) {
        HSSFRow nextRow = null;
        //遍历json格式的字段描述,并横向生成单元格
        for (int i = 0; i < columns.size(); i++) {
            JSONObject column = (JSONObject) columns.get(i);
            JSONArray children = (JSONArray) column.get("children");
            if (children != null) {
                   //设置父表格,并返回下一个单元格的列数
                   nextCellIndex = setParentCellValue(sheet, cellStyle, row, 
                   nextCellIndex, column, children.size());
                   nextCellIndex = nextCellIndex + 1;
                   //因为存在子表格，所以生成下一行
                   if (nextRow == null) {
                       nextRow = sheet.createRow(++rowIndex);
                   }
                   //使子单元格的位置，回退的到起始位置
                   int subCellStartPosition = nextCellIndex - children.size();
                   //递归生成子单元格,这里参数可以简化
                   setSubCellValue(sheet, rowIndex, 
                 cellStyle, nextRow, subCellStartPosition, children);
               } else {
                   //如果不是复合表头，直接生成并设置单元格
                   nextCellIndex = setCellValue(sheet, cellStyle, row, nextCellIndex, column);
                   ++nextCellIndex;
            }
        }
        //跨行的单元格合并
        mergeRowByColumn(sheet, rowIndex, columns, nextRow, cellStyle);
        //递归，生成这一行的单元格，并返回当前行数
        return rowIndex;
    }
    //设置复合单元格的父表格
    private int setParentCellValue(HSSFSheet sheet, HSSFCellStyle cellStyle, HSSFRow row, int cellIndex, 
        JSONObject field, int childrenSize) {
        cellIndex = setCellValue(sheet,cellStyle, row, cellIndex, field);
        int columnFrom = cellIndex;
        int columnTo = columnFrom + childrenSize - 1;
        createMergeCell(sheet, row, cellStyle, columnFrom, columnTo);
        return columnTo;
    }
    private int setCellValue(HSSFSheet sheet, HSSFCellStyle cellStyle, HSSFRow row, int cellIndex, JSONObject column) {
        HSSFCell subCell = row.createCell(cellIndex);
        subCell.setCellStyle(cellStyle);
        subCell.setCellValue(column.get("label").toString());
        return cellIndex;
    }