java ftp 连接报错！高手指教

我用java 连接 ftp 每隔一分钟下载多个文件，但是 会报如下异常，高手请教一下！连接之后，每取一个文件 就报一个异常。到最后，报java.net.SocketException: Broken pipe[2011-11-01 15:21:23] [DEBUG] Connection closed without indication. - at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:74) 
org.apache.commons.net.ftp.FTPConnectionClosedException: Connection closed without indication.
        at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:297)
        at org.apache.commons.net.ftp.FTP.getReply(FTP.java:619)
        at org.apache.commons.net.ftp.FTPClient.completePendingCommand(FTPClient.java:1244)
        at com.edu.jxt.business.FtpXmlClient.downXmlFileStream(FtpXmlClient.java:190)
        at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:64)
        at com.edu.jxt.business.ReceiveBossThread.run(ReceiveBossThread.java:43)
        at java.lang.Thread.run(Thread.java:595)
[2011-11-01 15:21:23] [DEBUG] ReceiveBossThread 文件提取 ADC270_AHB3911628_20111101151918_T164.dat - at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:63) 
[2011-11-01 15:21:23] [DEBUG] Connection closed without indication. - at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:74) 
org.apache.commons.net.ftp.FTPConnectionClosedException: Connection closed without indication.
        at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:297)
        at org.apache.commons.net.ftp.FTP.getReply(FTP.java:619)
        at org.apache.commons.net.ftp.FTPClient.completePendingCommand(FTPClient.java:1244)
        at com.edu.jxt.business.FtpXmlClient.downXmlFileStream(FtpXmlClient.java:190)
        at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:64)
        at com.edu.jxt.business.ReceiveBossThread.run(ReceiveBossThread.java:43)
        at java.lang.Thread.run(Thread.java:595)[2011-11-01 15:21:23] [DEBUG] ReceiveBossThread 文件提取 ADC270_AHB3911628_20111101151918_T164.dat - at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:63) 
[2011-11-01 15:21:23] [DEBUG] Connection closed without indication. - at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:74) 
org.apache.commons.net.ftp.FTPConnectionClosedException: Connection closed without indication.
        at org.apache.commons.net.ftp.FTP.__getReply(FTP.java:297)
        at org.apache.commons.net.ftp.FTP.getReply(FTP.java:619)
        at org.apache.commons.net.ftp.FTPClient.completePendingCommand(FTPClient.java:1244)
        at com.edu.jxt.business.FtpXmlClient.downXmlFileStream(FtpXmlClient.java:190)
        at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:64)
        at com.edu.jxt.business.ReceiveBossThread.run(ReceiveBossThread.java:43)
        at java.lang.Thread.run(Thread.java:595)[2011-11-01 15:21:23] [DEBUG] Broken pipe - at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:88) 
java.net.SocketException: Broken pipe
        at java.net.SocketOutputStream.socketWrite0(Native Method)
        at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92)
        at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
        at sun.nio.cs.StreamEncoder$CharsetSE.writeBytes(StreamEncoder.java:336)
        at sun.nio.cs.StreamEncoder$CharsetSE.implFlushBuffer(StreamEncoder.java:404)
        at sun.nio.cs.StreamEncoder$CharsetSE.implFlush(StreamEncoder.java:408)
        at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:152)
        at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:213)
        at java.io.BufferedWriter.flush(BufferedWriter.java:236)
        at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:472)
        at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:534)
        at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:583)
        at org.apache.commons.net.ftp.FTP.quit(FTP.java:794)
        at org.apache.commons.net.ftp.FTPClient.logout(FTPClient.java:697)
        at com.edu.jxt.business.FtpXmlClient.closeServer(FtpXmlClient.java:99)
        at com.edu.jxt.business.ReceiveBossThread.execute(ReceiveBossThread.java:86)
        at com.edu.jxt.business.ReceiveBossThread.run(ReceiveBossThread.java:43)
        at java.lang.Thread.run(Thread.java:595)