帮我用java实现pdf盖章效果

好的，实现PDF盖章效果主要有两个步骤：

1. 生成印章图片

印章图片可以在PS、AI等软件中设计，也可以使用Java代码生成。这里演示使用Java代码生成一个简单的圆形印章图片：

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class SealGenerator {
    private static final int IMAGE_SIZE = 200;
    private static final int PADDING = 20;
    private static final int CIRCLE_SIZE = 160;
    private static final String FONT_NAME = "微软雅黑";
    private static final int FONT_SIZE = 30;
    private static final String TEXT = "印";

    public static void main(String[] args) throws IOException {
        BufferedImage image = new BufferedImage(IMAGE_SIZE, IMAGE_SIZE, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = image.createGraphics();
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, IMAGE_SIZE, IMAGE_SIZE);
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g.setColor(Color.RED);
        g.fillOval(PADDING, PADDING, CIRCLE_SIZE, CIRCLE_SIZE);
        g.setColor(Color.WHITE);
        g.setFont(new Font(FONT_NAME, Font.PLAIN, FONT_SIZE));
        int textWidth = g.getFontMetrics().stringWidth(TEXT);
        g.drawString(TEXT, IMAGE_SIZE / 2 - textWidth / 2, IMAGE_SIZE / 2 + FONT_SIZE / 2);
        g.dispose();
        ImageIO.write(image, "png", new File("seal.png"));
    }
}

运行后会生成一个名称为`seal.png`的印章图片。

2. 在PDF上盖章

使用Java代码在PDF上盖章需要使用第三方库，这里演示使用iText库。

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import com.itextpdf.io.image.ImageDataFactory;
import com.itextpdf.kernel.geom.Rectangle;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfReader;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.canvas.PdfCanvas;
import com.itextpdf.layout.Document;
import com.itextpdf.layout.element.Image;

public class PdfSeal {
    private static final String INPUT_FILE = "input.pdf";
    private static final String OUTPUT_FILE = "output.pdf";
    private static final String SEAL_FILE = "seal.png";
    private static final float SEAL_X = 400;
    private static final float SEAL_Y = 100;
    private static final float SEAL_WIDTH = 100;
    private static final float SEAL_HEIGHT = 100;

    public static void main(String[] args) throws IOException {
        PdfReader reader = new PdfReader(INPUT_FILE);
        PdfWriter writer = new PdfWriter(new FileOutputStream(new File(OUTPUT_FILE)));
        PdfDocument pdf = new PdfDocument(reader, writer);
        Document document = new Document(pdf);
        Image seal = new Image(ImageDataFactory.create(SEAL_FILE));
        seal.scaleToFit(SEAL_WIDTH, SEAL_HEIGHT);
        seal.setFixedPosition(SEAL_X, SEAL_Y);
        PdfCanvas canvas = new PdfCanvas(pdf.getFirstPage());
        Rectangle rect = new Rectangle(SEAL_X, SEAL_Y, SEAL_WIDTH, SEAL_HEIGHT);
        canvas.rectangle(rect);
        canvas.stroke();
        document.add(seal);
        document.close();
    }
}

运行后会在PDF的第一页上添加一个印章。其中`INPUT_FILE`为输入PDF文件路径，`OUTPUT_FILE`为输出PDF文件路径，`SEAL_FILE`为印章图片路径，`SEAL_X`、`SEAL_Y`、`SEAL_WIDTH`、`SEAL_HEIGHT`分别为印章在PDF中的位置和大小。

希望这个简单的示例能对您有所帮助！