背景

曾几何时，我们总是提心吊胆的使用POI来处理Excel文件，一个3M的文件需要100多兆的内存空间。然而现在我们可以对它Say No，因为阿里巴巴的Easyexcel来了。

Maven坐标

 com.alibaba
 easyexcel
 2.1.4

示例代码包含以下功能：（1）自定义列宽的实现；（2）单元格字体颜色根据单元格的值动态调整。

public static void downloadExcel(String path, List> heads, List> datas) {
 OutputStream outputStream = null;
 try {
  outputStream = new FileOutputStream(path);
  CustomCellStyleStrategy styleStrategy = getStyleStrategy();  // 列宽设置
  CustomColumnWidthStyleStrategy columnWidthStyleStrategy = new CustomColumnWidthStyleStrategy();
  //第一个Sheet
  WriteSheet writeSheet = EasyExcel.writerSheet(0, "信息").head(heads).build();
  // 如果是浏览器下载, 需要设置不关闭流
  ExcelWriter excelWriter = EasyExcel.write(outputStream).autoCloseStream(Boolean.FALSE)
    .excelType(ExcelTypeEnum.XLSX).registerWriteHandler(styleStrategy)
    .registerWriteHandler(columnWidthStyleStrategy).build();
  excelWriter.write(datas, writeSheet);
  excelWriter.finish();
 } catch (Exception e) {
 } finally {
  // 如果是浏览器下载不需要关闭流
  
   IOUtils.closeQuietly(outputStream)
 }
}

参数path是Excel下载地址；heads是列表的头；datas是列表数据；

样式设置

public static CustomCellStyleStrategy getStyleStrategy() {
 //表头样式
 WriteCellStyle headWriteCellStyle = new WriteCellStyle();
 //设置表头居中对齐
 headWriteCellStyle.setHorizontalAlignment(HorizontalAlignment.CENTER); //背景色
 headWriteCellStyle.setFillPatternType(FillPatternType.SOLID_FOREGROUND); headWriteCellStyle.setFillForegroundColor(IndexedColors.LIGHT_GREEN.getIndex()); // 字体策略
 WriteFont headWriteFont = new WriteFont();
 // 字体大小
 headWriteFont.setFontName("微软雅黑");
 headWriteFont.setBold(true);
 headWriteFont.setFontHeightInPoints((short) 10);
 headWriteCellStyle.setWriteFont(headWriteFont); //设置 自动换行
 // headWriteCellStyle.setWrapped(true);
 //设置 垂直居中
 headWriteCellStyle.setVerticalAlignment(VerticalAlignment.CENTER); //内容样式
 WriteCellStyle contentWriteCellStyle = new WriteCellStyle();
 //设置内容靠居中对齐
 contentWriteCellStyle.setHorizontalAlignment(HorizontalAlignment.CENTER); contentWriteCellStyle.setVerticalAlignment(VerticalAlignment.CENTER); WriteFont contentWriteFont = new WriteFont();
 // 字体大小
 contentWriteFont.setFontName("微软雅黑");
 contentWriteFont.setBold(false);
 contentWriteFont.setFontHeightInPoints((short) 9);
 contentWriteCellStyle.setWriteFont(contentWriteFont); contentWriteCellStyle.setWrapped(true);
 CustomCellStyleStrategy horizontalCellStyleStrategy = new CustomCellStyleStrategy(headWriteCellStyle, contentWriteCellStyle);
 return horizontalCellStyleStrategy;
}

CustomCellStyleStrategy单元格字体颜色动态调整

public class CustomCellStyleStrategy extends AbstractCellStyleStrategy {
    private WriteCellStyle headWriteCellStyle;
    private WriteCellStyle contentWriteCellStyle;
    private CellStyle headCellStyle;
    public CustomCellStyleStrategy(WriteCellStyle headWriteCellStyle, WriteCellStyle contentWriteCellStyle) {
        this.headWriteCellStyle = headWriteCellStyle;
        this.contentWriteCellStyle = contentWriteCellStyle;
    }    protected void initCellStyle(Workbook workbook) {
        if (this.headWriteCellStyle != null) {
            this.headCellStyle = StyleUtil.buildHeadCellStyle(workbook, this.headWriteCellStyle);
        }    }    protected void setHeadCellStyle(Cell cell, Head head, Integer relativeRowIndex) {
        if (this.headCellStyle != null) {
            cell.setCellStyle(this.headCellStyle);
        }    }    protected void setContentCellStyle(Cell cell, Head head, Integer relativeRowIndex) {
    }    private void setContentCellStyle(WriteSheetHolder writeSheetHolder, Cell cell, Head head, Integer relativeRowIndex) {
        Workbook workbook = writeSheetHolder.getSheet().getWorkbook();        WriteFont contentWriteFont = new WriteFont();
        // 字体大小
        contentWriteFont.setFontName("微软雅黑");
        contentWriteFont.setBold(false);
        contentWriteFont.setFontHeightInPoints((short) 9);
        int columIndex = cell.getColumnIndex();
        String value = cell.getStringCellValue();
        double doubleValue = Double.parseDouble(value);
        if (doubleValue < 0.0) {
            contentWriteFont.setColor(IndexedColors.GREEN.getIndex());
        } else {
            contentWriteFont.setColor(IndexedColors.RED.getIndex());
        }
        contentWriteCellStyle.setWriteFont(contentWriteFont);
        CellStyle cellStyle = StyleUtil.buildContentCellStyle(workbook, contentWriteCellStyle);
        cell.setCellStyle(cellStyle);
    }
    public void afterCellDispose(WriteSheetHolder writeSheetHolder, WriteTableHolder writeTableHolder, List cellDataList, Cell cell, Head head, Integer relativeRowIndex, Boolean isHead) {
        if (isHead != null && head != null) {
            if (isHead.booleanValue()) {
                this.setHeadCellStyle(cell, head, relativeRowIndex);
            } else {
                this.setContentCellStyle(writeSheetHolder, cell, head, relativeRowIndex);
            }
        }
    }
}

CustomColumnWidthStyleStrategy列宽设置

public class CustomColumnWidthStyleStrategy extends AbstractColumnWidthStyleStrategy {
    protected void setColumnWidth(WriteSheetHolder writeSheetHolder,
                                  List cellDataList, Cell cell,
                                  Head head, Integer relativeRowIndex, Boolean isHead) {
        if (!isHead) {
            return;
        }        int columIndex = cell.getColumnIndex();
        // 设置列的宽度
        writeSheetHolder.getSheet().setColumnWidth(columIndex,
                ColumnEnum.getWidthByIndex(columIndex));
    }
}

ColumnEnum枚举类，只有核心代码，其余代码自己补齐

COLUMN_0(0, "字段1", 8 * 256),
COLUMN_1(1, "字段2", 10 * 256);
public static int getWidthByIndex(int index) {
 for (ColumnEnum item : ColumnEnum.values()) {
  if (item.index == index) {
   return item.width;
  } } return 10 * 256;
}

数据构造

public static void main(String[] args) {
 String path = "D:/export/test.xlsx";
 List> heads = new ArrayList<>();
 heads.add(Arrays.asList("字段1"));
 heads.add(Arrays.asList("字段2"));
 List> datas = new ArrayList<>();
 List