工作需要使用了org.apache.commons.net.ftp.FTPClient來操作FTP，記錄一下心得。

這個類封裝的很完善，使用起來也很簡單，只是在使用retrieveFileStream的時候碰到了一點小問題，就是不知道怎么完成傳輸狀態，嘗試發送abor指令也不行。查看了源代碼之后看到這一段說明以后解決問題：

* You must close the InputStream when you
* finish reading from it. The InputStream itself will take care of
* closing the parent data connection socket upon being closed. To
* finalize the file transfer you must call
* {@link #completePendingCommand completePendingCommand } and
* check its return value to verify success.

代碼如下：

import org.apache.commons.net.ftp.FTPClient; 
  
public class TestFTP { 
  
    public static void main(String[] args) { 
        try { 
            FTPClient ftp = new FTPClient(); 
            // initialize ftp connection 
            /* 
             * 
             */ 
  
            String remotefile = "test.xml"; 
            InputStream is = null; 
  
            is = ftp.retrieveFileStream(remotefile); 
  
            if (is != null) { 
                is.close(); 
            } 
  
            if (!ftp.completePendingCommand()) { 
                ftp.logout(); 
                ftp.disconnect(); 
            } 
            
            // continue 
        } catch (SocketException e) { 
            // TODO Auto-generated catch block 
            e.printStackTrace(); 
        } catch (IOException e) { 
            // TODO Auto-generated catch block 
            e.printStackTrace(); 
        } 
    } 
}