正确检查FTP服务器连接 [英] Properly check FTP server connection

问题描述

在我对服务器执行操作之前，我想检查连接是否成功建立。最简单的快速方式，所以如果连接没有了，我会尝试再次连接。

我使用此代码来执行此操作：

  private boolean checkConnection（）
 {
 try 
 {
布尔成功= ftpClient.login（user_name，密码） ; 
 if（成功）
返回true; 
 else 
返回false; 
 
 
 $ / code> 

但是这种方法在连接时会抛出一个NullPointer异常关闭。

我可以用 ftpClient.connect（server，port）; 来检查连接，但这就像再次重新连接。

检查连接的方式是什么？

解决方案试着发送简单的 sendNoOp（）并检查回复可能是轻松检查连接的好方法：

  private boolean checkConnectionWithOneRetry（）
 {
 try 
 {
 //向FTP发送一个NOOP命令服务器。 
布尔答案= ftpClient.sendNoOp（）; 
 if（answer）
 return true; 
 else 
 {
 System.out.println（服务器连接失败！）; 
布尔成功= reconnect（）; 
 if（成功）
 {
 System.out.println（重新连接attampt已成功！）; 
返回true; 
} 
 else 
 {
 System.out.println（重新连接attampt失败！）; 
返回false; 
 
 
 $ b catch（FTPConnectionClosedException e）
 {
 System.out.println（服务器连接已关闭！）; 
 boolean recon = reconnect（）; 
 if（recon）
 {
 System.out.println（Ret attampt have succeeded！）; 
返回true; 
} 
 else 
 {
 System.out.println（重新连接attampt失败！）; 
返回false; 
 
 
 $ b catch（IOException e）
 {
 System.out.println（服务器连接失败！）; 
 boolean recon = reconnect（）; 
 if（recon）
 {
 System.out.println（Ret attampt have succeeded！）; 
返回true; 
} 
 else 
 {
 System.out.println（重新连接attampt失败！）; 
返回false; 
 
 
 catch（NullPointerException e）
 {
 System.out.println（服务器连接已关闭！）; 
 boolean recon = reconnect（）; 
 if（recon）
 {
 System.out.println（Ret attampt have succeeded！）; 
返回true; 
} 
 else 
 {
 System.out.println（重新连接attampt失败！）; 
返回false; 
} 
} 
} 
  

I open a connection to an FTP server at the start of my program.

Before I perform operations on the server I want to check if the connection was successfully established. The easiest fast manner so if the connection is gone, I will try to connect again.

I used this code to do this:

private boolean checkConnection()
{
    try 
    {
        boolean success = ftpClient.login(user_name, password);
        if(success)
            return true;
        else 
            return false;
    }
}

But this method throws a NullPointer exception when the connection was closed.

I can check the connection with the ftpClient.connect(server, port); but that is like attampting to connect all over again.

What is the bes way to check the connection?

解决方案

Trying to send a simple sendNoOp() and checking the reply might be a good way to lightly check the connecion:

private boolean checkConnectionWithOneRetry()
{
    try 
    {
        // Sends a NOOP command to the FTP server. 
        boolean answer = ftpClient.sendNoOp();
        if(answer)
            return true;
        else
        {
            System.out.println("Server connection failed!");
            boolean success = reconnect();
            if(success)
            {
                System.out.println("Reconnect attampt have succeeded!");
                return true;
            }
            else
            {
                System.out.println("Reconnect attampt failed!");
                return false;
            }
        }
    }
    catch (FTPConnectionClosedException e) 
    {
        System.out.println("Server connection is closed!");
        boolean recon = reconnect();
        if(recon)
        {
            System.out.println("Reconnect attampt have succeeded!");
            return true;
        }
        else
        {
            System.out.println("Reconnect attampt have failed!");
            return false;
        }

    }
    catch (IOException e) 
    {
        System.out.println("Server connection failed!");
        boolean recon = reconnect();
        if(recon)
        {
            System.out.println("Reconnect attampt have succeeded!");
            return true;
        }
        else
        {
            System.out.println("Reconnect attampt have failed!");
            return false;
        }   
    }
    catch (NullPointerException e) 
    {
        System.out.println("Server connection is closed!");
        boolean recon = reconnect();
        if(recon)
        {
            System.out.println("Reconnect attampt have succeeded!");
            return true;
        }
        else
        {
            System.out.println("Reconnect attampt have failed!");
            return false;
        }   
    }
}

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