FtpClient问题

请问，我 用FtpClient类的.get()方法，下载FTP上的文件，但是怎么也下不来，最后提示java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:113)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read(BufferedInputStream.java:235)
at sun.net.TransferProtocolClient.readServerResponse(TransferProtocolClient.java:49)
at sun.net.ftp.FtpClient.readReply(FtpClient.java:217)
at sun.net.ftp.FtpClient.issueCommand(FtpClient.java:193)
at sun.net.ftp.FtpClient.openDataConnection(FtpClient.java:420)
at sun.net.ftp.FtpClient.get(FtpClient.java:550)
at ftp.FtpUtil.download(FtpUtil.java:124)
at com.lingtu.lbs.gf.main.GfClient.downData(GfClient.java:491)
at com.lingtu.lbs.gf.main.GfClient.main(GfClient.java:163)
java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(SocketInputStream.java:113)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read(BufferedInputStream.java:235)
at sun.net.TransferProtocolClient.readServerResponse(TransferProtocolClient.java:49)
at sun.net.ftp.FtpClient.readReply(FtpClient.java:217)
at sun.net.ftp.FtpClient.issueCommand(FtpClient.java:193)
at sun.net.ftp.FtpClient.closeServer(FtpClient.java:168)
at ftp.FtpUtil.closeServer(FtpUtil.java:200)
at com.lingtu.lbs.gf.main.GfClient.downData(GfClient.java:509)
at com.lingtu.lbs.gf.main.GfClient.main(GfClient.java:163)
请问什么原因。