如果支持https，将HttpURLConnection 改为HttpsURLConnection 即可

import=Java.Net.*；

import Java.io.*；

  public boolean saveUrlAs(String photoUrl, String fileName) {
    try {
      URL url = new URL(photoUrl);
      HttpURLConnection connection = (HttpURLConnection) url.openConnection();
      DataInputStream in = new DataInputStream(connection.getInputStream());
      DataOutputStream out = new DataOutputStream(new FileOutputStream(fileName));
      byte[] buffer = new byte[4096];
      int count = 0;
      while ((count = in.read(buffer)) > 0) {
        out.write(buffer, 0, count);
      }
      out.close();
      in.close();
      return true;
    }
    catch (Exception e) {
      return false;
    }
  }

public String getDocumentAt(String urlString) {
//兼容FTP协议
    StringBuffer document = new StringBuffer();
    try {
      URL url = new URL(urlString);
      URLConnection conn = url.openConnection();
      BufferedReader reader = new BufferedReader(new InputStreamReader(conn.
          getInputStream()));
      String line = null;
      while ( (line = reader.readLine()) != null) {
        document.append(line + "n");
      }
      reader.close();
    }
    catch (MalformedURLException e) {
      System.out.println("Unable to connect to URL: " + urlString);
    }
    catch (IOException e) {
      System.out.println("IOException when connecting to URL: " + urlString);
    }
    return document.toString();
  }
//测试
  String photoUrl = http://www.xrss.cn/b.cer;
  String fileName = photoUrl.substring(photoUrl.lastIndexOf("/"));
  String filePath = "d:/";
  boolean flag = saveUrlAs(photoUrl, filePath + fileName);
  out.println("Get URL file " + flag);