使用jsch进行sftp传输时遇到的问题com.jcraft.jsch.JSchException: Session.connect: java.net.SocketException: Connection reset

在做某个业务时，需要将文件传输到另一台服务器，指定使用sftp方式；于是在网上找到jsch包使用，原先代码大致如下：

ChannelSftp channelSftp = null;
        try {
            JSch jsch = new JSch();
            jsch.getSession("ftpUserName", "ftpHost", 22);
            Session sshSession = jsch.getSession("ftpUserName", "ftpHost", 22);
            System.out.println("Session created.");
            sshSession.setPassword("ftpPassword");
            Properties sshConfig = new Properties();
            sshConfig.put("StrictHostKeyChecking", "no");
            sshSession.setConfig(sshConfig);
            sshSession.connect();
            System.out.println("Session connected.");
            System.out.println("Opening Channel.");
            Channel channel = sshSession.openChannel("sftp");
            channel.connect();
            channelSftp = (ChannelSftp) channel;

            //todo 上传文件
        } catch (Exception e) {
            //todo 异常处理
        } finally {
            //断开sftp连接
            if (channelSftp != null) {
                channelSftp.disconnect();
            }
        }

程序运行后大约过了几天，发现日志产生大量连接异常的日志，主要是两类异常：SocketException和NoRouteToHostException

com.jcraft.jsch.JSchException: Session.connect: java.net.SocketException: Connection reset
    at com.jcraft.jsch.Session.connect(Session.java:534)
    at com.jcraft.jsch.Session.connect(Session.java:162)
    at sun.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:84)
    at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)



com.jcraft.jsch.JSchException: java.net.NoRouteToHostException: Cannot assign requested address (Address not available)
	at com.jcraft.jsch.Util.createSocket(Util.java:344)
	at com.jcraft.jsch.Session.connect(Session.java:194)
	at com.jcraft.jsch.Session.connect(Session.java:162)
	at sun.reflect.GeneratedMethodAccessor37.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:84)
	at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
	at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.net.NoRouteToHostException: Cannot assign requested address (Address not available)
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
	at java.net.Socket.connect(Socket.java:589)
	at java.net.Socket.connect(Socket.java:538)
	at java.net.Socket.<init>(Socket.java:434)
	at java.net.Socket.<init>(Socket.java:211)
	at com.jcraft.jsch.Util.createSocket(Util.java:338)
	... 17 common frames omitted

 

首先我百度了下，找到有人提到修改socket连接的配置，于是我尝试修改：

1. 修改端口释放后的等待时间为30s。echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout

2. 修改/proc/sys/net/ipv4/tcp_tw_reuse为1。echo 1 > /proc/sys/net/ipv4/tcp_tw_reuse

3. 修改/proc/sys/net/ipv4/tcp_tw_recycle为1。echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle

4.增加可用端口  vim /etc/sysctl.conf 

net.ipv4.ip_local_port_range = 10000     65000      -----意味着10000~65000端口可用 

改完后，执行命令“sysctl -p”使参数生效。

 

修改配置后，重启程序，发现过了一天，仍然出现上述的问题；继续百度查看，发现有人提到连接关闭的问题，于是查了下服务器的ssh连接数

netstat |grep ssh |wc -l

这一查，发现有5500多个连接未关闭（随着时间推移，空闲连接会自动关闭），于是问题的原因大致定位到了：程序生成连接的速度大于连接释放的速度；但是问题的根源还是在于，程序没有正确关闭连接。

不仅仅要断开channel，还要断开session。修改后的代码如下：

ChannelSftp channelSftp = null;
        try {
            JSch jsch = new JSch();
            jsch.getSession("ftpUserName", "ftpHost", 22);
            Session sshSession = jsch.getSession("ftpUserName", "ftpHost", 22);
            System.out.println("Session created.");
            sshSession.setPassword("ftpPassword");
            Properties sshConfig = new Properties();
            sshConfig.put("StrictHostKeyChecking", "no");
            sshSession.setConfig(sshConfig);
            sshSession.connect();
            System.out.println("Session connected.");
            System.out.println("Opening Channel.");
            Channel channel = sshSession.openChannel("sftp");
            channel.connect();
            channelSftp = (ChannelSftp) channel;

            //todo 上传文件
        } catch (Exception e) {
            //todo 异常处理
        } finally {
            //断开sftp连接
            if (channelSftp != null) {
                try {
                    channelSftp.disconnect();
                    //关闭会话
                    Session session = channelSftp.getSession();
                    if (session != null) {
                        session.disconnect();
                    }
                } catch (Exception e) {
                    //todo 异常处理
                }
            }
        }

重新运行，观察ssh连接数，发现恢复正常，每次文件传输完毕后，会话及时结束。