POI介绍

ApachePOI是用Java编写的免费开源的跨平台的JavaAPI，ApachePOI提供API给Java程序对MicrosoftOffice格式档案读和写的功能，其中使用最多的就是使用POI操作Excel文件。

maven坐标依赖

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<dependency>
        <groupId>org.apache.poi</groupId>
          <artifactId>poi</artifactId>
 </dependency>

 <dependency>
       <groupId>org.apache.poi</groupId>
       <artifactId>poi-ooxml</artifactId>
 </dependency>

POI结构：

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HSSF－提供读写MicrosoftExcelXLS格式档案的功能
XSSF－提供读写MicrosoftExcelOOXMLXLSX格式档案的功能
HWPF－提供读写MicrosoftWordDOC格式档案的功能
HSLF－提供读写MicrosoftPowerPoint格式档案的功能
HDGF－提供读MicrosoftVisio格式档案的功能
HPBF－提供读MicrosoftPublisher格式档案的功能
HSMF－提供读MicrosoftOutlook格式档案的功能

关于POI中基础API的使用，就不多介绍了，本文主要介绍对excel的处理-两个excel之间的数据拷贝

话不多说，现在开始！！

单元格样式个数限制

首先介绍一下POI中excel的单元格样式，工作簿Workbook中单元格样式个数是有限制的，所以在 程序中应该重复使用相同CellStyle，而不是为每个单元 格创建一个CellStyle

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HSSFCellStyle - 4000个
XSSFCellStyle - 64000个
最大行数 最大列数 单元格样式个数 文本单元格最大长度 一个单元格上条件样式最大个数
HSSF 65536 256(2^8) 4000 32767 3
XSSF 1048576 16384(2^14) 64000 Integer.MAX_VALUE

其实在Workbook的createCellStyle()方法中，可以看到各个表格格式实现类对单元格样式的限制

如HSSFCellStyle：

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   /**
    * The maximum number of cell styles in a .xls workbook.
    * The 'official' limit is 4,000, but POI allows a slightly larger number.
    * This extra delta takes into account built-in styles that are automatically
    *
    * See http://office.microsoft.com/en-us/excel-help/excel-specifications-and-limits-HP005199291.aspx
    */
   private static final int MAX_STYLES = 4030;

/**
    * Create a new Cell style and add it to the workbook's style table.
    * You can define up to 4000 unique styles in a .xls workbook.
    *
    * @return the new Cell Style object
    * @throws IllegalStateException if the number of cell styles exceeded the limit for this type of Workbook.
    */
   @Override
   public HSSFCellStyle createCellStyle()
   {
       if(workbook.getNumExFormats() == MAX_STYLES) {
           throw new IllegalStateException("The maximum number of cell styles was exceeded. " +
                   "You can define up to 4000 styles in a .xls workbook");
       }
       ExtendedFormatRecord xfr = workbook.createCellXF();
       short index = (short) (getNumCellStyles() - 1);
       return new HSSFCellStyle(index, xfr, this);
   }

HSSFCellStyle：

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    /**
     * Excel2007
     *
     * <ul>
     * <li>The total number of available rows is 1M (2^20)</li>
     * <li>The total number of available columns is 16K (2^14)</li>
     * <li>The maximum number of arguments to a function is 255</li>
     * <li>Number of conditional format conditions on a cell is unlimited
     * (actually limited by available memory in Excel)</li>
     * <li>Number of cell styles is 64000</li>
     * <li>Length of text cell contents is 32767</li>
     * <ul>
     */
    EXCEL2007(0x100000, 0x4000, 255, Integer.MAX_VALUE, 64000, 32767);

// Is this right? Number formats (XSSFDataFormat) and cell styles (XSSFCellStyle) are different. What's up with the plus 1?
    private static final int MAXIMUM_STYLE_ID = SpreadsheetVersion.EXCEL2007.getMaxCellStyles();

public XSSFCellStyle createCellStyle() {
        if (this.getNumCellStyles() > MAXIMUM_STYLE_ID) {
            throw new IllegalStateException("The maximum number of Cell Styles was exceeded. You can define up to " + MAXIMUM_STYLE_ID + " style in a .xlsx Workbook");
        } else {
            int xfSize = this.styleXfs.size();
            CTXf xf = org.openxmlformats.schemas.spreadsheetml.x2006.main.CTXf.Factory.newInstance();
            xf.setNumFmtId(0L);
            xf.setFontId(0L);
            xf.setFillId(0L);
            xf.setBorderId(0L);
            xf.setXfId(0L);
            int indexXf = this.putCellXf(xf);
            return new XSSFCellStyle(indexXf - 1, xfSize - 1, this, this.theme);
        }
    }

所以，如果在拷贝两个Workbook的数据时，数据单元格数量过多，频繁使用createCellStyle()方法创建单元格样式，会导致单元格样式超出限制。

所以，为了解决单元格样式限制问题，可以将样式缓存起来，具体方法可见如下代码

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package com.huoli.ctar.cms.poi;

import lombok.Data;
import org.apache.poi.hssf.usermodel.HSSFCellStyle;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

import java.text.SimpleDateFormat;
import java.util.*;

/**
 * Author:   caijc
 * Date:     2022/1/5 10:28
 * Description:
 */
@Data
public class POICopyHandler {

    // 缓存单元格的样式索引，key是拷贝原表格的样式索引id,value是拷贝目标表格的样式id
    Map<Short,Short> styleMap = new HashMap<>();
    private Workbook fromWorkbook;
    private Workbook toWorkbook;
    private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

    // 构造方法，将原表格的所有样式一并拷贝到目标表格，并将表格样式索引缓存
    public POICopyHandler(Workbook fromWorkbook, Workbook toWorkbook) {
        this.fromWorkbook = fromWorkbook;
        this.toWorkbook = toWorkbook;
        Sheet fromSheet = fromWorkbook.getSheetAt(0);
        Sheet toSheet = fromWorkbook.getSheetAt(0);
        if (toSheet == null){
            toWorkbook.createSheet();
        }
        for (int i = fromSheet.getFirstRowNum(); i <= fromSheet.getLastRowNum(); i++) {
            Row fromRow = fromSheet.getRow(i);
            for (int j = fromRow.getFirstCellNum(); j < fromRow.getPhysicalNumberOfCells(); j++) {
                Cell fromCell = fromRow.getCell(j);
                CellStyle fromStyle = fromCell.getCellStyle();
                if(!styleMap.containsKey(fromStyle.getIndex())){
                    CellStyle toStyle = toWorkbook.createCellStyle();
                    toStyle.cloneStyleFrom(fromStyle);
                    styleMap.put(fromStyle.getIndex(), toStyle.getIndex());
                }
            }
        }

    }

    /**
     * 复制行
     * 此方法主要用于复制2个不同Workbook间的行
     */
    public void copySingleRows(int fromSheetIndex, int toSheetIndex, int fromRowIndex, int toRowIndex) {
        Sheet fromSheet = fromWorkbook.getSheetAt(fromSheetIndex);
        Sheet toSheet = toWorkbook.getSheetAt(toSheetIndex);

        if ((fromRowIndex == -1) || (fromRowIndex == -1)) {
            return;
        }

        // 设置列宽
        Row fromRow = fromSheet.getRow(fromRowIndex);
        if (fromRow == null) {
            return;
        }
        for (int i = fromRow.getLastCellNum(); i >= fromRow.getFirstCellNum(); i--) {
            toSheet.setColumnWidth(i, fromSheet.getColumnWidth(i));
            toSheet.setColumnHidden(i, false);
        }
        // 拷贝行并填充数据
        Row toRow = toSheet.createRow(toRowIndex);
        toRow.setHeight(fromRow.getHeight());
        for (int j = fromRow.getFirstCellNum(); j <= fromRow.getPhysicalNumberOfCells(); j++) {
            Cell fromCell = fromRow.getCell(j);
            Cell toCell = toRow.createCell(j);
            if (fromCell != null) {
                CellStyle fromStyle = fromCell.getCellStyle();
                CellStyle toStyle = toWorkbook.getCellStyleAt(styleMap.get(fromStyle.getIndex()));
                if (toStyle != null){
                    toCell.setCellStyle(toStyle);
                }
                switch (fromCell.getCellTypeEnum()) {
                    case BOOLEAN:
                        toCell.setCellValue(fromCell.getBooleanCellValue());
                        break;
                    case ERROR:
                        toCell.setCellErrorValue(fromCell.getErrorCellValue());
                        break;
                    case FORMULA:
                        toCell.setCellFormula(parseFormula(fromCell.getCellFormula()));
                        break;
                    case NUMERIC:
                        if(DateUtil.isCellDateFormatted(fromCell)){
                            toCell.setCellValue(sdf.format(fromCell.getDateCellValue()));
                        } else{
                            toCell.setCellValue(fromCell.getNumericCellValue());
                        }
                        break;
                    case STRING:
                        toCell.setCellValue(fromCell.getRichStringCellValue());
                        break;
                }
            }

        }
    }

    private String parseFormula(String pPOIFormula) {
        final String cstReplaceString = "ATTR(semiVolatile)"; //$NON-NLS-1$
        StringBuffer result;
        int index;

        result = new StringBuffer();
        index = pPOIFormula.indexOf(cstReplaceString);
        if (index >= 0) {
            result.append(pPOIFormula, 0, index);
            result.append(pPOIFormula.substring(index + cstReplaceString.length()));
        } else {
            result.append(pPOIFormula);
        }

        return result.toString();
    }
}

调用示例：

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POICopyHandler poiCopyHandler = new POICopyHandler(fromWorkbook, toWorkbook);
poiCopyHandler.copySingleRows(0,0,0,0);// 四个参数分别是：源Workbook的sheet索引，目标Workbook的sheet索引，源Workbook的行索引，目标Workbook的行索引