需要的库

  <!-- 生成pdf--><dependency><groupId>com.itextpdf</groupId><artifactId>itextpdf</artifactId><version>5.5.10</version></dependency><!-- https://mvnrepository.com/artifact/commons-net/commons-net FTPClient --><dependency><groupId>commons-net</groupId><artifactId>commons-net</artifactId><version>3.6</version></dependency>

代码一，生成本地pdf文件

if (list.size() > 0) {Document document = new Document();FTPClient ftp = new FTPClient();try {//1、创建一个document对象//2、创建一个PdfWriter实例FileData fileData1=list.get(0);String filenamePdf=fileData1.getCatalogname()+fileData1.getCatalogid()+".pdf";PdfWriter.getInstance(document, new FileOutputStream(filenamePdf));//3、打开文档document.open();int pagenum = 0;for (FileData filePage : list) {//页码pagenum++;String folder = filePage.getFolder();//服务器主机String host = filePage.getHost();//服务器端口int port = Integer.parseInt(filePage.getPort());//登录用户名String username = filePage.getUsername();//登录密码String pwd = filePage.getPassword();ftp.setControlEncoding(filePage.getEncoding());ftp.addProtocolCommandListener(new PrintCommandListener(new PrintWriter(System.out)));ftp.connect(host, port);if (!FTPReply.isPositiveCompletion(ftp.getReplyCode())) {ftp.disconnect();}ftp.login(username, pwd);ftp.setFileType(FTP.BINARY_FILE_TYPE);ftp.enterLocalPassiveMode();ftp.changeWorkingDirectory(folder);final ByteArrayOutputStream bos = new ByteArrayOutputStream();ftp.retrieveFile(filePage.getFilename(), bos);Image img = Image.getInstance(bos.toByteArray());img.setAlignment(Image.ALIGN_CENTER);// 根据图片大小设置页面，一定要先设置页面，再newPage（），否则无效document.setPageSize(new Rectangle(img.getWidth(), img.getHeight()));document.newPage();document.add(img);}} catch (Exception e) {e.printStackTrace();} finally {try {ftp.logout();} catch (IOException e) {e.printStackTrace();}try {ftp.disconnect();} catch (IOException e) {e.printStackTrace();}if (document.isOpen()) {document.close();}}}

代码二、生成pdf直接发送到响应中

上方代码加入和替换此两行，请求添加在游览器可以直接预览，页面调用打印方法
页面参数直接在后端取

 response.setContentType("application/pdf;charset=utf-8");PdfWriter.getInstance(document, response.getOutputStream());

<body>
<iframe style="display: none;" id="printIframe" src="/controllers/viewimagecontroller/printImageByPageIds.do"></iframe>
<script type="text/javascript">$(function () {doPrint();});//点击打印按钮，触发事件】function doPrint(){$("#printIframe")[0].contentWindow.print();}
</script>
</body>