FTP    java.net.ConnectException: Connection refused: connect

排查問題如下： 一般是埠寫錯引起的 

（1）：利用linux命令檢視埠  netstat -auntp | grep 21

Last login: Fri Oct 28 12:12:24 2016 from 116.226.185.223
[[email protected] ~]# netstat -auntp | grep 21
tcp        0      0 0.0.0.0:2121                0.0.0.0:*                   LISTEN      20143/vsftpd        
tcp        0      0 :::3306                     :::*                        LISTEN      2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33699      ESTABLISHED 2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33700      ESTABLISHED 2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33661      ESTABLISHED 2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33688      ESTABLISHED 2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33625      ESTABLISHED 2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33687      ESTABLISHED 2184/mysqld         
tcp        0      0 ::ffff:127.0.0.1:3306       ::ffff:127.0.0.1:33702      ESTABLISHED 2184/mysqld         
[
 
[email protected] ~]# 

（2）: 如果連線後  讀取資料為空 則  做如下修改：

ftp.enterLocalPassiveMode();//如果不加這個讀取資料會為空
FTPFile[] fs = ftp.listFiles();

（3）：完整程式碼如下：

public  void ReadFileFromSftp() {
 		
	String path="uploads//";
	String fileName="20161012buy.txt";
 		String result="";
 		FTPClient ftp = new FTPClient();
 		
 		try {
 			int reply;
 			//1.連線伺服器
 			ftp.connect(server,2121);
 			//2.登入伺服器 如果採用預設埠，可以使用ftp.connect(url)的方式直接連線FTP伺服器
 			ftp.login(user, password);
 			//3.判斷登陸是否成功
 			reply = ftp.getReplyCode();
 			if (!FTPReply.isPositiveCompletion(reply)) {
 				ftp.disconnect();
 			}
 			//4.指定要下載的目錄
 			ftp.changeWorkingDirectory(path);// 轉移到FTP伺服器目錄
 			//5.遍歷下載的目錄
 			ftp.enterLocalPassiveMode();
 			FTPFile[] fs = ftp.listFiles();
 			for (FTPFile ff : fs) {
 				//解決中文亂碼問題，兩次解碼
 				byte[] bytes=ff.getName().getBytes("iso-8859-1");
 				String fn=new String(bytes,"utf8");
 				if (fn.equals(fileName)) {
 					InputStream  inputStream=ftp.retrieveFileStream(ff.getName());
 					result = IOUtils.toString(inputStream);
 				}
 				
 			}
 			ftp.logout();
 		} catch (IOException e) {
 			e.printStackTrace();
 		} finally {
 			if (ftp.isConnected()) {
 				try {
 					ftp.disconnect();
 				} catch (IOException ioe) {
 				}
 			}
 		}
 		
 		System.out.println("result"+result);
 		
 	}
}