easyexcel导出合并单元格

吐槽：网络上有很多人在贡献自己的代码，但是极其相似可以作为参考。如下：
（https://cloud.tencent.com/developer/article/1671316，https://www.it610.com/article/1296421123914801152.htm 等等）

前言：网络上easyexcel合并的文章都使用的是“CellWriteHandler”,其实还有“RowWriteHandler”。此片文章将为大家提供一个按照行来合并单元格的做法

1.按行合并的策略ExcelMergeRowByRowUtil

public class ExcelMergeRowByRowUtil implements RowWriteHandler {
    private int mergeRowIndex;//从哪一行开始合并
    private int[] mergeColumnIndex;//excel合并的列
    private int signNum;//合并的唯一标识
    private int total;//总行数

    private int lastRow;
    private int firstCol;
    private int lastCol;
    private int firstRow;

    private int mergeCount =1;

    public ExcelMergeRowByRowUtil(int mergeRowIndex, int[] mergeColumnIndex, int signNum, int total) {
        this.mergeRowIndex = mergeRowIndex;
        this.mergeColumnIndex = mergeColumnIndex;
        this.signNum = signNum;
        this.total = total;
    }

    @Override
    public void beforeRowCreate(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder, Integer rowIndex, Integer relativeRowIndex, Boolean isHead) {

    }

    @Override
    public void afterRowCreate(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder, Row row, Integer relativeRowIndex, Boolean isHead) {

    }

    @Override
    public void afterRowDispose(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder, Row row, Integer relativeRowIndex, Boolean isHead) {
        //当前行
        int curRowIndex = row.getRowNum();
        //每一行的最大列数
        short lastCellNum = row.getLastCellNum();

        if(curRowIndex == 1){
            //赋初值 第一行
            firstRow = curRowIndex;
        }
        //开始合并位置
        if(curRowIndex > mergeRowIndex && !row.getCell(0).getStringCellValue().equals("")){
            for (int i = 0; i < lastCellNum; i++) {
                if(i == mergeColumnIndex[i]){
                    //当前行号 当前行对象 合并的标识位
                    mergeWithPrevAnyRow(writeSheetHolder.getSheet(),curRowIndex,row,signNum);
                    break;//已经进入到合并单元格操作里面了，执行一次就行
                }

            }
        }
    }

    public void mergeWithPrevAnyRow(Sheet sheet,int curRowIndex,Row row,int signNum){
        Object currentData = row.getCell(signNum).getCellTypeEnum() == CellType.STRING ? row.getCell(signNum).getStringCellValue() : row.getCell(signNum).getNumericCellValue();
        Row preRow = row.getSheet().getRow(curRowIndex - 1);
        Object preData = preRow.getCell(signNum).getCellTypeEnum() == CellType.STRING ? preRow.getCell(signNum).getStringCellValue() : preRow.getCell(signNum).getNumericCellValue();
        //判断是否合并单元格
        boolean curEqualsPre = currentData.equals(preData);
        //判断前一个和后一个相同 并且 标识位相同
        if (curEqualsPre){
            lastRow = curRowIndex;
            mergeCount++;
        }
        //excel过程中合并
        if(!curEqualsPre && mergeCount>1){
            mergeSheet(firstRow,lastRow,mergeColumnIndex,sheet);
            mergeCount = 1;
        }

        //excel结尾处合并
        if (mergeCount>1 && total==curRowIndex){
            mergeSheet(firstRow,lastRow,mergeColumnIndex,sheet);
            mergeCount = 1;
        }

        if (!curEqualsPre){
            firstRow = curRowIndex;
        }

    }

    private void mergeSheet(int firstRow,int lastRow,int[] mergeColumnIndex,Sheet sheet){
        for (int colNum : mergeColumnIndex){
            firstCol = colNum;
            lastCol = colNum;
            CellRangeAddress cellRangeAddress = new CellRangeAddress(firstRow,lastRow,firstCol,lastCol);
            sheet.addMergedRegion(cellRangeAddress);
        }
    }
}

2.easyexcel组装的model

@Getter
@Setter
@ContentRowHeight(15) //内容行高
@HeadRowHeight(20)//表头行高
public class ExcelModel {
    /**oss模板名称*/
    public static final String RESEXCELNAME = "document.xlsx";
    public static final String TEMPLATEEXCELNAME = "文章管理";
    public static final String SUFFIX = ".xlsx";

    /**
     * notice
     * 当采用模板上传Excel且.needHead(false)设置了不生成标题头  @ColumnWidth(10)标签将无效，根据模板头的长度来走
     */
    @ColumnWidth(10)//单元格长度
    @ExcelProperty(value = "序号", index = 0)
    private String order;

    @ColumnWidth(20)//单元格长度
    @ExcelProperty(value = "文章标题", index = 1)
    private String title;

    @ColumnWidth(15)//单元格长度
    @ExcelProperty(value = "单位", index = 2)
    private String company;

    @ColumnWidth(15)//单元格长度
    @ExcelProperty(value = "编号", index = 3)
    private String documentCode;

    @ColumnWidth(12)//单元格长度
    @ExcelProperty(value = "发文日期", index = 4)
    private String publishDate;

    @ColumnWidth(25)//单元格长度
    @ExcelProperty(value = "意见", index = 5)
    private String idea;

    @ColumnWidth(15)//单元格长度
    @ExcelProperty(value = "事件详情事项", index = 6)
    private String workDetails;

    @ColumnWidth(15)//单元格长度
    @ExcelProperty(value = "截止时间", index = 7)
    private String dueTime;

    @ColumnWidth(20)//单元格长度
    @ExcelProperty(value = "负责人", index = 8)
    private String name;

    @ColumnWidth(15)//单元格长度
    @ExcelProperty(value = "备注", index = 9)
    private String remarks;

3.list组装excel并合并单元格

public void getEasyExcel(List list){
        int[] mergeColumeIndex = {0,1,2,3,4,5};//需要合并的列
        int mergeRowIndex = 1;// 从那一行开始合并
        //合并单元格
//      ExcelMergeUtil excelFillCellMergeStrategy = new ExcelMergeUtil(mergeRowIndex,mergeColumeIndex);
        ExcelMergeRowByRowUtil excelMergeRowByRowStrategy = new ExcelMergeRowByRowUtil(mergeRowIndex,mergeColumeIndex,mergeColumeIndex[0],documentExcelList.size());
        //设置头样式
        WriteCellStyle headWriteCellStyle = new WriteCellStyle();
        
        //设置内容格式
        WriteCellStyle contentWriteCellStyle = new WriteCellStyle();
        
        HorizontalCellStyleStrategy horizontalCellStyleStrategy =
                new HorizontalCellStyleStrategy(headWriteCellStyle,contentWriteCellStyle);
        
        //2.excel转outputStream
        //拼装excel字节数组outputStream
        ByteArrayOutputStream out = new ByteArrayOutputStream();

        EasyExcel.write(out, DocumentExcelModel.class)
//              .withTemplate(in)
//              .needHead(false)//是否需要excel自定义模板的标题头
                .registerWriteHandler(horizontalCellStyleStrategy)
                .registerWriteHandler(excelMergeRowByRowStrategy)
//              .registerWriteHandler(excelFillCellMergeStrategy)//此处为网络上按照每个单元格进行合并
                .sheet("sheet")
                .doWrite(list);
    
}

ExcelMergeRowByRowUtil合并单元格的思路：
1.读取每一行，如果上一行和当前行唯一标识位相同，mergeCount累加。当上一行和当前行唯一标识位不相同的时候进行合并单元格。
2.当读取到最后一行符合合并条件的时候进行合并单元格。

ExcelMergeRowByRowUtil implements RowWriteHandler 与网上 ExcelMergeUtil implements CellWriteHandler的区别
CellWriteHandler实现的方法是按照cell为单元进行处理的，假如每一行有十列，则需要比对十次。
RowWriteHandler实现的方法是按照row为单位尽心处理的，粒度更粗一写。控制好操作excel速度会更快。