Java PDF生成水印 代码

使用 Java 可以使用 Apache PDFBox 库来生成 PDF 文档的水印。以下是一个示例代码：

import java.io.File;
import java.io.IOException;

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageContentStream;
import org.apache.pdfbox.pdmodel.font.PDFont;
import org.apache.pdfbox.pdmodel.font.PDType1Font;

public class AddWatermark {
    public static void main(String[] args) throws IOException {
        // Load the PDF document
        File file = new File("input.pdf");
        PDDocument document = PDDocument.load(file);

        // Create a font object
        PDFont font = PDType1Font.HELVETICA_BOLD;

        // Iterate over each page of the document
        for (PDPage page : document.getPages()) {
            // Start a new content stream which will "hold" the to be created content
            PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true);

            // Set the font and font size
            contentStream.setFont(font, 36);

            // Set the color of the text
            contentStream.setNonStrokingColor(255, 255, 255);

            // Define the text to be added as watermark
            String text = "CONFIDENTIAL";

            // Get the width of the text
            float textWidth = font.getStringWidth(text) / 1000 * 36;

            // Get the height of the text
            float textHeight = font.getFontDescriptor().getFontBoundingBox().getHeight() / 1000 * 36;

            // Calculate the position of the text
            float x = (page.getMediaBox().getWidth() - textWidth) / 2;
            float y = (page.getMediaBox().getHeight() - textHeight) / 2;

            // Rotate the text 45 degrees counterclockwise
            contentStream.saveGraphicsState();
            contentStream.transform(Matrix.getRotateInstance(-45, x, y));

            // Draw the text on the page
            contentStream.beginText();
            contentStream.newLineAtOffset(x, y);
            contentStream.showText(text);
            contentStream.endText();

            // Restore the graphics state
            contentStream.restoreGraphicsState();

            // Close the content stream
            contentStream.close();
        }

        // Save the PDF document
        document.save("output.pdf");

        // Close the document
        document.close();
    }
}

这段代码会读取名为 `input.pdf` 的文档，在每一页上生成一个文本水印 “CONFIDENTIAL”，并将生成的文档保存为 `output