easyexcel導出合併單元格

吐槽：網絡上有很多人在貢獻自己的代碼，但是極其相似可以作爲參考。如下：
（https://cloud.tencent.com/developer/article/1671316，https://www.it610.com/article/1296421123914801152.htm 等等）

前言：網絡上easyexcel合併的文章都使用的是“CellWriteHandler”,其實還有“RowWriteHandler”。此片文章將爲大家提供一個按照行來合併單元格的做法

1.按行合併的策略ExcelMergeRowByRowUtil

public class ExcelMergeRowByRowUtil implements RowWriteHandler {
    private int mergeRowIndex;//從哪一行開始合併
    private int[] mergeColumnIndex;//excel合併的列
    private int signNum;//合併的唯一標識
    private int total;//總行數

    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) {
        //當前行
        int curRowIndex = row.getRowNum();
        //每一行的最大列數
        short lastCellNum = row.getLastCellNum();

        if(curRowIndex == 1){
            //賦初值 第一行
            firstRow = curRowIndex;
        }
        //開始合併位置
        if(curRowIndex > mergeRowIndex && !row.getCell(0).getStringCellValue().equals("")){
            for (int i = 0; i < lastCellNum; i++) {
                if(i == mergeColumnIndex[i]){
                    //當前行號 當前行對象 合併的標識位
                    mergeWithPrevAnyRow(writeSheetHolder.getSheet(),curRowIndex,row,signNum);
                    break;//已經進入到合併單元格操作裏面了，執行一次就行
                }

            }
        }
    }

    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();
        //判斷是否合併單元格
        boolean curEqualsPre = currentData.equals(preData);
        //判斷前一個和後一個相同 並且 標識位相同
        if (curEqualsPre){
            lastRow = curRowIndex;
            mergeCount++;
        }
        //excel過程中合併
        if(!curEqualsPre && mergeCount>1){
            mergeSheet(firstRow,lastRow,mergeColumnIndex,sheet);
            mergeCount = 1;
        }

        //excel結尾處合併
        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組裝的model

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

    /**
     * notice
     * 當採用模板上傳Excel且.needHead(false)設置了不生成標題頭  @ColumnWidth(10)標籤將無效，根據模板頭的長度來走
     */
    @ColumnWidth(10)//單元格長度
    @ExcelProperty(value = "序號", index = 0)
    private String order;

    @ColumnWidth(20)//單元格長度
    @ExcelProperty(value = "文章標題", index = 1)
    private String title;

    @ColumnWidth(15)//單元格長度
    @ExcelProperty(value = "單位", index = 2)
    private String company;

    @ColumnWidth(15)//單元格長度
    @ExcelProperty(value = "編號", index = 3)
    private String documentCode;

    @ColumnWidth(12)//單元格長度
    @ExcelProperty(value = "發文日期", index = 4)
    private String publishDate;

    @ColumnWidth(25)//單元格長度
    @ExcelProperty(value = "意見", index = 5)
    private String idea;

    @ColumnWidth(15)//單元格長度
    @ExcelProperty(value = "事件詳情事項", index = 6)
    private String workDetails;

    @ColumnWidth(15)//單元格長度
    @ExcelProperty(value = "截止時間", index = 7)
    private String dueTime;

    @ColumnWidth(20)//單元格長度
    @ExcelProperty(value = "負責人", index = 8)
    private String name;

    @ColumnWidth(15)//單元格長度
    @ExcelProperty(value = "備註", index = 9)
    private String remarks;

3.list組裝excel併合並單元格

public void getEasyExcel(List<ExcelModel> list){
        int[] mergeColumeIndex = {0,1,2,3,4,5};//需要合併的列
        int mergeRowIndex = 1;// 從那一行開始合併
        //合併單元格
//      ExcelMergeUtil excelFillCellMergeStrategy = new ExcelMergeUtil(mergeRowIndex,mergeColumeIndex);
        ExcelMergeRowByRowUtil excelMergeRowByRowStrategy = new ExcelMergeRowByRowUtil(mergeRowIndex,mergeColumeIndex,mergeColumeIndex[0],documentExcelList.size());
        //設置頭樣式
        WriteCellStyle headWriteCellStyle = new WriteCellStyle();
        
        //設置內容格式
        WriteCellStyle contentWriteCellStyle = new WriteCellStyle();
        
        HorizontalCellStyleStrategy horizontalCellStyleStrategy =
                new HorizontalCellStyleStrategy(headWriteCellStyle,contentWriteCellStyle);
        
        //2.excel轉outputStream
        //拼裝excel字節數組outputStream
        ByteArrayOutputStream out = new ByteArrayOutputStream();

        EasyExcel.write(out, DocumentExcelModel.class)
//              .withTemplate(in)
//              .needHead(false)//是否需要excel自定義模板的標題頭
                .registerWriteHandler(horizontalCellStyleStrategy)
                .registerWriteHandler(excelMergeRowByRowStrategy)
//              .registerWriteHandler(excelFillCellMergeStrategy)//此處爲網絡上按照每個單元格進行合併
                .sheet("sheet")
                .doWrite(list);
    
}

ExcelMergeRowByRowUtil合併單元格的思路：
1.讀取每一行，如果上一行和當前行唯一標識位相同，mergeCount累加。當上一行和當前行唯一標識位不相同的時候進行合併單元格。
2.當讀取到最後一行符合合併條件的時候進行合併單元格。

ExcelMergeRowByRowUtil implements RowWriteHandler 與網上 ExcelMergeUtil implements CellWriteHandler的區別
CellWriteHandler實現的方法是按照cell爲單元進行處理的，假如每一行有十列，則需要比對十次。
RowWriteHandler實現的方法是按照row爲單位盡心處理的，粒度更粗一寫。控制好操作excel速度會更快。