Question

我运行ftp文件传输程序时，总会出现这个问题，求哪位大神帮我看一下，不胜感激啊

at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:529)
at java.net.Socket.connect(Socket.java:478)
at sun.net.NetworkClient.doConnect(NetworkClient.java:163)
at sun.net.NetworkClient.openServer(NetworkClient.java:118)
at sun.net.ftp.FtpClient.openServer(FtpClient.java:488)
at sun.net.ftp.FtpClient.openServer(FtpClient.java:475)
at com.cjg.ftp.FtpTools.connectServer(FtpTools.java:58)
at com.cjg.ftp.FtpDownFile.downFileTest(FtpDownFile.java:21)
at com.cjg.ftp.FtpDownFile.main(FtpDownFile.java:36)
Exception in thread "main" java.lang.NullPointerException
at sun.net.TransferProtocolClient.sendServer(TransferProtocolClient.java:101)
at sun.net.ftp.FtpClient.issueCommand(FtpClient.java:192)
at sun.net.ftp.FtpClient.openPassiveDataConnection(FtpClient.java:268)
at sun.net.ftp.FtpClient.openDataConnection(FtpClient.java:375)
at sun.net.ftp.FtpClient.get(FtpClient.java:550)
at com.cjg.ftp.FtpTools.downloadFile(FtpTools.java:303)
at com.cjg.ftp.FtpDownFile.downFileTest(FtpDownFile.java:23)
at com.cjg.ftp.FtpDownFile.main(FtpDownFile.java:36)

Answer 1

Exception in thread "main" java.lang.NullPointerException有空指针了，单步跟踪一下，看看那儿出问题了