java easyexcel 自定义水印插件

Java EasyExcel 是一款非常好用的 Excel 操作工具，提供了丰富的 API 接口，可以方便地进行 Excel 文件的读写操作。而在实际应用中，我们可能需要在 Excel 文件中添加一些自定义的水印，以便于区分文件的来源或者保护文件的安全性。本文将介绍如何使用 Java EasyExcel 自定义水印插件。

1. 创建水印插件类

首先，我们需要创建一个自定义的水印插件类，实现 com.alibaba.excel.write.handler.WriteHandler 接口，该接口提供了 beforeSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) 方法，允许我们在生成 Excel 文件之前对 Sheet 进行一些自定义操作。以下是一个简单的水印插件类示例：

public class WaterMarkHandler implements WriteHandler {
 
    private String waterMark; // 水印内容
 
    public WaterMarkHandler(String waterMark) {
        this.waterMark = waterMark;
    }
 
    @Override
    public void beforeSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        Sheet sheet = writeSheetHolder.getSheet();
        Drawing<?> drawing = sheet.createDrawingPatriarch();
        // 创建水印文本框
        ClientAnchor anchor = drawing.createAnchor(0, 0, 0, 0, 0, 0, 10, 10);
        Textbox textBox = drawing.createTextbox(anchor);
        // 设置文本框属性
        textBox.setLineStyleColor(255, 255, 255);
        textBox.setFillColor(255, 255, 255);
        textBox.setVerticalAlignment(VerticalAlignment.CENTER);
        textBox.setHorizontalAlignment(HorizontalAlignment.CENTER);
        textBox.setText(new HSSFRichTextString(waterMark));
    }
 
    @Override
    public void afterSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        // do nothing
    }
}

在上面的代码中，我们通过实现 beforeSheetCreate() 方法，在生成 Sheet 之前创建了一个水印文本框，并设置了文本框的属性和文本内容。

2. 使用水印插件

在使用 Java EasyExcel 生成 Excel 文件时，我们可以将上面定义的 WaterMarkHandler 类作为参数传递给 ExcelWriter 的构造函数，从而实现添加自定义水印的功能。以下是一个简单的示例：

public void writeExcelWithWaterMark(OutputStream outputStream, List<List<String>> data, String waterMark) throws IOException {
    ExcelWriter writer = new ExcelWriter(outputStream, ExcelTypeEnum.XLSX);
    WriteSheet sheet = new WriteSheet();
    sheet.setSheetName("Sheet1");
    sheet.setClazz(String.class);
    sheet.setHead(Collections.emptyList());
    sheet.setTableStyle(new TableStyle());
    sheet.setWriteHandler(new WaterMarkHandler(waterMark)); // 设置水印插件
    writer.write1(data, sheet);
    writer.finish();
}

在上面的代码中，我们通过调用 setWriteHandler() 方法将 WaterMarkHandler 对象传递给 WriteSheet，从而在生成 Excel 文件时添加自定义水印。完整的代码实现可以参考下面的示例：

import com.alibaba.excel.ExcelWriter;
import com.alibaba.excel.metadata.TableStyle;
import com.alibaba.excel.metadata.VerticalAlignment;
import com.alibaba.excel.metadata.WriteSheet;
import com.alibaba.excel.write.handler.WriteHandler;
import com.alibaba.excel.write.handler.WriteHandlerHolder;
import com.alibaba.excel.write.handler.WriteWorkbookHolder;
import com.alibaba.excel.write.handler.context.CellWriteHandlerContext;
import com.alibaba.excel.write.handler.context.RowWriteHandlerContext;
import com.alibaba.excel.write.handler.context.SheetWriteHandlerContext;
import org.apache.poi.hssf.usermodel.HSSFRichTextString;
import org.apache.poi.ss.usermodel.HorizontalAlignment;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.VerticalAlignment;
import org.apache.poi.ss.usermodel.drawing.ClientAnchor;
import org.apache.poi.ss.usermodel.drawing.Drawing;
import org.apache.poi.ss.usermodel.drawing.Textbox;
import org.apache.poi.ss.util.CellAddress;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Collections;
import java.util.List;

public class WaterMarkHandler implements WriteHandler {

    private String waterMark;

    public WaterMarkHandler(String waterMark) {
        this.waterMark = waterMark;
    }

    @Override
    public void beforeSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        Sheet sheet = writeSheetHolder.getSheet();
        Drawing<?> drawing = sheet.createDrawingPatriarch();
        // 创建水印文本框
        ClientAnchor anchor = drawing.createAnchor(0, 0, 0, 0, 0, 0, 10, 10);
        Textbox textBox = drawing.createTextbox(anchor);
        // 设置文本框属性
        textBox.setLineStyleColor(255, 255, 255);
        textBox.setFillColor(255, 255, 255);
        textBox.setVerticalAlignment(VerticalAlignment.CENTER);
        textBox.setHorizontalAlignment(HorizontalAlignment.CENTER);
        textBox.setText(new HSSFRichTextString(waterMark));
    }

    @Override
    public void afterSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        // do nothing
    }

    public static void writeExcelWithWaterMark(OutputStream outputStream, List<List<String>> data, String waterMark) throws IOException {
        ExcelWriter writer = new ExcelWriter(outputStream, ExcelTypeEnum.XLSX);
        WriteSheet sheet = new WriteSheet();
        sheet.setSheetName("Sheet1");
        sheet.setClazz(String.class);
        sheet.setHead(Collections.emptyList());
        sheet.setTableStyle(new TableStyle());
        sheet.setWriteHandler(new WaterMarkHandler(waterMark));
        writer.write1(data, sheet);
        writer.finish();
    }
}

这样，我们就可以使用 Java EasyExcel 实现自定义水印插件的功能了。