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，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。

@RequestMapping("previewFile")
	public void download(String filePath ,HttpServletRequest request,HttpServletResponse response) throws Exception {
		
		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";
		}else if (extension.equals("txt")){
			contentType = "text/plain";
		}else if (extension.equals("doc") || extension.equals("docx")){
			contentType = "application/pdf";
			try {
				br = convertToPdf(filePath);
			}catch (Exception e){
			}
		}else if (extension.equals("jpg") || extension.equals("jpeg")){
			contentType = "image/jpeg";
		}else if (extension.equals("png")){
			contentType = "image/png";
		}else if (extension.equals("gif")){
			contentType = "image/gif";
		}else if (extension.equals("gif")){
			contentType = "image/gif";
		}
		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 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) 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);
		// 将字节数组转换为字节输入流
		ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
		// 返回BufferedInputStream
		return new BufferedInputStream(byteArrayInputStream);
	}