通过文件路径获取文件，对不同类型的文件进行不同处理，将Word文件转成pdf文件预览，并早呢更加水印，暂不支持Excel文件，如果浏览器不支持PDF文件预览需要下载插件。文中currentUser.getUserid()，即为增加的水印内容，需要替换掉，字符串类型的。

加水印用的包是pdfbox，不是itext7，这两个包有的方法名一致，但是穿的参数类型不一致，引用的包不对，会报错。BufferedImage引用的是java.awt.image.BufferedImage引用成pdfbox的也会报错，有报错的参数注意一下引用的包。

<dependency><groupId>org.apache.pdfbox</groupId><artifactId>pdfbox</artifactId><version>2.0.24</version>
</dependency>

@RequestMapping("previewFile")public void download(String src,HttpServletRequest request,HttpServletResponse response) throws Exception {String filePath = src;System.out.println("filePath:" + filePath);File f = new File(filePath);if (!f.exists()) {response.sendError(404, "File not found!");return;}String fileName = f.getName();String extension = getFileExtension(f.getName());BufferedInputStream br = new BufferedInputStream(new FileInputStream(f));byte[] bs = new byte[1024];int len = 0;response.reset(); // 非常重要URL u = new URL("file:///" + filePath);//String contentType = u.openConnection().getContentType();String contentType = "";if(extension.equals("pdf")){contentType = "application/pdf";br = addWatermarkToPdf(filePath, currentUser.getUserid());}else if (extension.equals("txt")){contentType = "text/plain";}else if (extension.equals("doc") || extension.equals("docx")){contentType = "application/pdf";try {br = convertToPdf(filePath,currentUser.getUserid());}catch (Exception e){}}else if (extension.equals("jpg") || extension.equals("jpeg")){contentType = "image/jpeg";br = createWatermarkedImage(filePath, currentUser.getUserid());}else if (extension.equals("png")){contentType = "image/png";br = createWatermarkedImage(filePath, currentUser.getUserid());}else if (extension.equals("gif")){contentType = "image/gif";br = createWatermarkedImage(filePath, currentUser.getUserid());}//Document docsss = new Document(filePath);response.setContentType(contentType+"; charset=UTF-8");response.setHeader("Content-Disposition", "inline;filename="+ fileName);// 文件名应该编码成utf-8，注意：使用时，我们可忽略这句OutputStream out = response.getOutputStream();while ((len = br.read(bs)) > 0) {out.write(bs, 0, len);}out.flush();out.close();br.close();}public static BufferedInputStream createWatermarkedImage(String imagePath, String watermarkText) throws IOException {// 读取原始图片File file = new File(imagePath);BufferedImage targetImg = ImageIO.read(new FileInputStream(file));int height = targetImg.getHeight();int width = targetImg.getWidth();//-------------------------文字水印 start----------------------------BufferedImage waterMarkImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 创建画笔Graphics2D graphics2D = waterMarkImage.createGraphics();// 绘制原始图片graphics2D.drawImage(targetImg, 0, 0, width, height, null);// 设置水印颜色graphics2D.setColor(new Color(255, 255, 255, 255));double scale = 1.0;if(width < height){scale = (double) width / height;}int fontSize = (int) Math.ceil((double) (height / 25) * scale);// 设置字体 画笔字体样式为微软雅黑，加粗，文字大小按比例给graphics2D.setFont(new Font("微软雅黑", Font.BOLD, fontSize));float alpha = 0.7f; // 设置透明度为50%AlphaComposite composite = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha);graphics2D.setComposite(composite);// 水印旋转度graphics2D.rotate(Math.toRadians(-25), (double) width / 2, (double) height / 2);int x = -width * 3;int y;// 计算水印文字的宽度FontMetrics fontMetrics = graphics2D.getFontMetrics();int watermarkWidth = fontMetrics.stringWidth(watermarkText);// 水印横向间隔int positionWidth = (int)(width * 0.12);// 水印竖向间隔int positionHeight  = (int)(height * 0.12);while (x < width * 3) {y = -height * 3;while (y < height * 3) {graphics2D.drawString(watermarkText, x, y);y += fontSize + positionWidth;}x += watermarkWidth + positionHeight;}graphics2D.dispose();ByteArrayOutputStream outputStream = new ByteArrayOutputStream();ImageIO.write(waterMarkImage, "png", outputStream);byte[] imageBytes = outputStream.toByteArray();return new BufferedInputStream(new ByteArrayInputStream(imageBytes));}public static BufferedInputStream addWatermarkToPdf(String filePath,String userId) throws IOException {// 加载PDF文档PDDocument document = PDDocument.load(new File(filePath));try {// 遍历所有页面for (PDPage page : document.getPages()) {// 获取页面的媒体框（即页面的大小）PDRectangle mediaBox = page.getMediaBox();float pageWidth = mediaBox.getWidth();float pageHeight = mediaBox.getHeight();// 创建内容流，使用APPEND模式PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true, true);// 设置水印字体和大小contentStream.setFont(PDType1Font.HELVETICA_BOLD, 36);// 设置水印颜色（RGB）contentStream.setNonStrokingColor(200, 200, 200);// 设置文本水印的参数String watermarkText = userId;PDType1Font font = PDType1Font.HELVETICA_BOLD;float fontSize = 20;float textWidth = font.getStringWidth(watermarkText) / 1000 * fontSize;float textHeight = fontSize;float xStep = pageWidth / 4; // 文本在x轴上的重复间隔float yStep = pageHeight / 12; // 文本在y轴上的重复间隔，可以根据需要调整// 绘制文本水印for (float y = 0; y < pageHeight; y += yStep) {for (float x = 0; x < pageWidth; x += xStep) {// 设置文本颜色（RGB），这里使用白色以确保在红色背景上可见contentStream.setStrokingColor(255, 255, 255);// 设置字体和大小contentStream.beginText();contentStream.setFont(font, fontSize);contentStream.newLineAtOffset(x, y);// 设置文本旋转//contentStream.newLineAtOffset(xx, yy);//contentStream.setTextMatrix(0, -0.5f, 0.5f, 0, 0, 0);contentStream.setTextMatrix(0.5f, 0.5f, -0.5f, 0.5f, x, y);contentStream.showText(watermarkText);contentStream.endText();}}// 关闭内容流contentStream.close();}ByteArrayOutputStream outputStream = new ByteArrayOutputStream();document.save(outputStream);document.close();return new BufferedInputStream(new ByteArrayInputStream(outputStream.toByteArray()));// 保存并关闭PDF文档//document.save(new File("watermarked.pdf"));//document.close();} finally {if (document != null) {document.close();}}}public static String getFileExtension(String fileName) {if (fileName == null || fileName.isEmpty()) {return "";}int dotIndex = fileName.lastIndexOf('.');if (dotIndex == -1 || dotIndex == fileName.length() - 1) {// No dot found or dot is at the end (e.g., "file.")return "";}return fileName.substring(dotIndex + 1);}public static BufferedInputStream convertToPdf(String wordFilePath,String userId) throws Exception {// 加载Word文档Document doc = new Document(wordFilePath);// 创建一个字节数组输出流来保存PDF内容ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();// 设置PDF保存选项（可选，这里使用默认设置）PdfSaveOptions saveOptions = new PdfSaveOptions();// 将文档保存为PDF格式到字节数组输出流中doc.save(byteArrayOutputStream, saveOptions);if (byteArrayOutputStream.size() == 0) {throw new IllegalArgumentException("ByteArrayOutputStream is empty");}// 将ByteArrayOutputStream的内容转换为ByteArrayInputStreamByteArrayInputStream bais = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());// 使用PDDocument.load方法将流转换为PDDocument对象PDDocument pdDocument = PDDocument.load(bais);// 关闭ByteArrayInputStreambais.close();// 将字节数组转换为字节输入流ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());// 返回BufferedInputStreamreturn addWatermarkToWord(pdDocument,userId);}public static BufferedInputStream addWatermarkToWord(PDDocument document,String userId) throws IOException {// 加载PDF文档//PDDocument document = PDDocument.load(new File(filePath));try {// 遍历所有页面for (PDPage page : document.getPages()) {// 获取页面的媒体框（即页面的大小）PDRectangle mediaBox = page.getMediaBox();float pageWidth = mediaBox.getWidth();float pageHeight = mediaBox.getHeight();// 创建内容流，使用APPEND模式PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true, true);// 设置水印字体和大小contentStream.setFont(PDType1Font.HELVETICA_BOLD, 36);// 设置水印颜色（RGB）contentStream.setNonStrokingColor(200, 200, 200);// 设置文本水印的参数String watermarkText = userId;PDType1Font font = PDType1Font.HELVETICA_BOLD;float fontSize = 20;float textWidth = font.getStringWidth(watermarkText) / 1000 * fontSize;float textHeight = fontSize;float xStep = pageWidth / 4; // 文本在x轴上的重复间隔float yStep = pageHeight / 12; // 文本在y轴上的重复间隔，可以根据需要调整// 绘制文本水印for (float y = 0; y < pageHeight; y += yStep) {for (float x = 0; x < pageWidth; x += xStep) {// 设置文本颜色（RGB），这里使用白色以确保在红色背景上可见contentStream.setStrokingColor(255, 255, 255);// 设置字体和大小contentStream.beginText();contentStream.setFont(font, fontSize);contentStream.newLineAtOffset(x, y);// 设置文本旋转//contentStream.newLineAtOffset(xx, yy);//contentStream.setTextMatrix(0, -0.5f, 0.5f, 0, 0, 0);contentStream.setTextMatrix(0.5f, 0.5f, -0.5f, 0.5f, x, y);contentStream.showText(watermarkText);contentStream.endText();}}// 关闭内容流contentStream.close();}ByteArrayOutputStream outputStream = new ByteArrayOutputStream();document.save(outputStream);document.close();return new BufferedInputStream(new ByteArrayInputStream(outputStream.toByteArray()));// 保存并关闭PDF文档//document.save(new File("watermarked.pdf"));//document.close();} finally {if (document != null) {document.close();}}}