JAVA实现从FTP中获取图片,并将图片转换成base64图片流,返回前端进行显示。

返回的是base64的编码的流,前端使用<img src="返回的值"/>  即可
@Transactional(readOnly = false)
public synchronized List<String> copyFileByBase64(Inner inn, String pages,
                                      Long lTime, HttpServletRequest request,StringBuffer filesN) throws Exception {
   List<Path> list = null;
   FTPClient ftp = null;
   List<String> fileNames = null;
   try{
      if (inn != null) {
         String filePath = inn.getFilepath().replace("\\", File.separator);
         //从数据库中获取FTP账号密码信息 替换成自己的就行
         list=printApplyDao.getPaths(filePath.substring(0, filePath.indexOf(File.separator)));
      }
      if (list != null && list.size() > 0) {
         //FTP登录 替换成自己的就行
         ftp = archivesService.getFtpClient(list.get(0));
      }
      if (ftp != null && !StringUtils.isEmpty(pages)) {
         String[] page = pages.split(",");
         String innerPath = inn.getFilepath().replace("\\", "/");
         String path = innerPath.substring(innerPath.indexOf("/") + 1);
         //设置主动模式，防止在Linux上，由于安全限制，可能某些端口没有开启，出现阻塞
         ftp.enterLocalPassiveMode();
         //ftp上的路径
         path = new String(path.getBytes("gbk"),"iso-8859-1");
         boolean changeWorkingDirectory = ftp.changeWorkingDirectory(path);
         //判断ftp目录是否切换成功
         if(changeWorkingDirectory){
            FTPFile[] files = ftp.listFiles();
            //对ftp文件进行排序，顺序排序
            Arrays.sort(files, new MySort());
            //将page字符串，转为数组
            List<Integer> listPage = convertToInt(page);
            String fileName = null;
            fileNames = new ArrayList<String>();
            ByteArrayOutputStream bos = null;
            for (Integer p : listPage) {
               long start = System.currentTimeMillis();
               if(p>=1){
                  //获取ftp上的文件名称
                  fileName = files[p - 1].getName();
               }else{
                  fileName = files[p - 0].getName();
               }
               //获取文件流
               InputStream retrieveFileStream = ftp.retrieveFileStream(new String(fileName.getBytes("gbk"), "ISO-8859-1"));
               filesN.append(fileName);
               if (null == retrieveFileStream) {
                  throw new FileNotFoundException(fileName);
               }
               bos = new ByteArrayOutputStream();
               int length;
               byte[] buf = new byte[2048];
               while (-1 != (length = retrieveFileStream.read(buf, 0, buf.length))) {
                  bos.write(buf, 0, length);
               }
               ByteArrayInputStream fis = new ByteArrayInputStream(bos.toByteArray());
               bos.flush();
               bos.close();
               byte[] buffer = new byte[fis.available()];
               int offset = 0;
               int numRead = 0;
               while (offset < buffer.length && (numRead = fis.read(buffer, offset, buffer.length - offset)) >= 0) {
                  offset += numRead;
               }
               if (offset != buffer.length) {
                  throw new IOException("Could not completely read file ");
               }
               fis.close();
               String asB64 = "data:image/jpg;base64,"+new Base64Encoder().encode(buffer);
               fileNames.add(asB64);
               long end = System.currentTimeMillis();
               System.out.println(end-start);
               retrieveFileStream.close();
               ftp.completePendingCommand();
            }
         }
      }
   }catch (Exception e) {
      e.printStackTrace();
   }finally{
      if(ftp!=null&&ftp.isConnected())
      {
         try {
            ftp.disconnect();
         } catch (IOException e) {
            e.printStackTrace();
         }
      }
   }
   return fileNames;
}

不要忘了添加jar包哦

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>4.0.9</version>
</dependency>

辛苦编码，希望可以得到支持，继续下去。