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一、背景

• 使用EasyExcel导出excel文件，但是需要同时导出图片信息，且图片信息不能影响行高和单元格宽度，图片本身被导出时，不能因为压缩导致图片变形

二、思路

• 使用EasyExcel最主要是要实现各种hadler，通过实现CellWriteHandler，获取单元格图片，进行图片压缩；
• 由于excel的行高和单元格宽度换算方式完全不一样，所以要通过计算得出最合适的压缩比例
• (excel宽度 / 字符宽度转换为标准字符宽度) * 估算的字符到像素的转换因子 = 宽度像素；
• (excel高度 / 点转换为英寸) * 英寸转换为像素 = 行高像素；
• 最终宽度像素或者行高像素 根据行高与像素的转换因子 ，计算出需要设置的单元格间距值，即可正常缩小图片

三、代码

public static class QuotationCustomCellWriteHandler implements CellWriteHandler {// 256分之一的字符宽度转换为标准字符宽度。public static final int STANDARD_CHARACTER_WIDTH = 256;// 7.5是一个估算的字符到像素的转换因子public static final float CHARACTER_2_PIXEL_FACTOR = 7.5f;// 将点转换为英寸，因为1点 = 1/72英寸。public static final int PIXEL_2_INCH_FACTOR = 72;// 英寸转换为像素，其中96是常用的DPI（每英寸像素数）值。public static final int DPI = 96;// 行高与像素的转换因子public static final float ROW_HEIGHT_2_PIXEL_FACTOR = 1.3333f;/*** 外界传入的行高，内部查不到*/private final int rowHeight;public QuotationCustomCellWriteHandler(int rowHeight) {this.rowHeight = rowHeight;}@Overridepublic void afterCellDataConverted(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder,WriteCellData<?> cellData, Cell cell, Head head, Integer relativeRowIndex,Boolean isHead) {boolean noImageValue = Objects.isNull(cellData) || cellData.getImageDataList() == null || cellData.getImageDataList().isEmpty();if (Objects.equals(Boolean.TRUE, isHead) || noImageValue) {return;}Sheet sheet = cell.getSheet();ImageData imageData = cellData.getImageDataList().get(0);imageData.setRelativeLastRowIndex(0);imageData.setRelativeLastColumnIndex(0);// 处理图像缩放 - 等比例缩放try (ByteArrayInputStream bis = new ByteArrayInputStream(imageData.getImage())) {BufferedImage image = ImageIO.read(bis);int targetWidth = (int) ((double) sheet.getColumnWidth(cell.getColumnIndex()) / STANDARD_CHARACTER_WIDTH * CHARACTER_2_PIXEL_FACTOR);int targetHeight = (int) (rowHeight * 1.0 / PIXEL_2_INCH_FACTOR * DPI);// 计算图像的缩放比例double scaleX = (double) targetWidth / image.getWidth();double scaleY = (double) targetHeight / image.getHeight();double scale = Math.min(scaleX, scaleY);// 计算缩放后的图像大小int scaledWidth = (int) (image.getWidth() * scale);int scaledHeight = (int) (image.getHeight() * scale);// 计算上下左右四个角的空白int topPadding = (targetHeight - scaledHeight) / 2;int bottomPadding = targetHeight - scaledHeight - topPadding;int leftPadding = (targetWidth - scaledWidth) / 2;int rightPadding = targetWidth - scaledWidth - leftPadding;// 行高（点）= 像素高度 / 1.3333imageData.setTop((int) (topPadding / ROW_HEIGHT_2_PIXEL_FACTOR));imageData.setBottom((int) (bottomPadding / ROW_HEIGHT_2_PIXEL_FACTOR));imageData.setLeft((int) (leftPadding / ROW_HEIGHT_2_PIXEL_FACTOR));imageData.setRight((int) (rightPadding / ROW_HEIGHT_2_PIXEL_FACTOR));} catch (Exception e) {log.error("QuotationCustomCellWriteHandler afterCellDataConverted err", e);}CellWriteHandler.super.afterCellDataConverted(writeSheetHolder, writeTableHolder, cellData, cell, head, relativeRowIndex, isHead);}}