I'm writing Java GUI program for static route management using SSH. My code is as follows:
import com.jcraft.jsch.*;
import java.io.*;
public class Konsep {
String status;
static String username;
static String hostname;
String inputcommand;
String output;
static Session session;
JSch jsch = new JSch();
public String status(String stringstatus) {
stringstatus = status;
return stringstatus;
}
public String InputCommand(String inputcommandstatus) {
inputcommandstatus = inputcommand;
return inputcommandstatus;
}
public void connect(String usernamelokal, String hostnamelokal,
String password, int port) {
// JSch jsch=new JSch();
try {
Session sessionlokal = jsch.getSession(usernamelokal,
hostnamelokal, port);
sessionlokal.setPassword(password);
UserInfo ui = new UserInfoku.Infoku();
sessionlokal.setUserInfo(ui);
sessionlokal.setTimeout(0);
sessionlokal.connect();
status = "tersambung \n";
username = usernamelokal;
hostname = hostnamelokal;
session = sessionlokal;
System.out.println(username + " " + hostname);
} catch (Exception e) {
System.out.println(e);
status = "Exception = \n " + e + "\n";
}
}
public void disconnect() {
// JSch jsch=new JSch();
try {
Session sessionlokal = jsch.getSession(username, hostname);
// System.out.println(username +" "+ hostname);
sessionlokal.disconnect();
status = "wes pedhoott \n";
} catch (Exception e) {
System.out.println(e);
status = "Exception = \n " + e + "\n";
}
}
public void addRoute() {
// JSch jsch=new JSch();
System.out.println(username + " " + hostname);
try {
Session sessionlokal = session; // =jsch.getSession(username, hostname);
Channel channel = sessionlokal.openChannel("exec");
((ChannelExec) channel).setCommand(inputcommand);
channel.setInputStream(null);
channel.connect();
((ChannelExec) channel).setErrStream(System.err);
InputStream in = channel.getInputStream();
channel.connect();
byte[] tmp = new byte[1024];
while (true) {
while (in.available() > 0) {
int i = in.read(tmp, 0, 1024);
if (i < 0)
break;
System.out.print(new String(tmp, 0, i));
}
if (channel.isClosed()) {
System.out.println("exit-status: "
+ channel.getExitStatus());
break;
}
try {
Thread.sleep(1000);
} catch (Exception ee) {
}
}
channel.disconnect();
} catch (Exception e) {
System.out.println(e);
}
}
}
The problem is when I call the connect method and then calling the addroute, the program returns
root 192.168.50.2
root 192.168.50.2
com.jcraft.jsch.JSchException: session is down
I've been trying to get session status with either
Session sessionlokal=session; //returns com.jcraft.jsch.JSchException: ChannelExec
or
Session sessionlokal=jsch.getSession(username, hostname); //returns session is down
I've also tried to use keepalive, but its not working either.
My intention is to create a session to host (log in), while leaving the session up, execute a command or commands and maybe executing other commands later, and then closing the session when its not needed (log out). I've been searching on this forum and I found this question but the code is create a method to define a command to execute first, and then creating the session, call the command's method and close the session.
Any ideas about how to do as I mentioned above ?
After trying Session.sendKeepAliveMsg() without success, I came to the following solution which seems to be rather stable:
private Session getSession() throws Exception {
try {
if (!session.isConnected()) {
logger.info("Session successfully tested, use it again.");
session.connect();
}
} catch (Throwable t) {
logger.info("Session terminated. Create a new one.");
session = jsch.getSession(user, host, port);
session.setConfig(config);
session.connect();
}
return session;
}
Update: Some days later it failed.
I tried to test it by killing the open session on the server. All prior versions I tested this way showed the exact same behavior, regardless whether the problem popped up after waiting some days or killing the server process, so I thought this test - and its outcome for the above solution - to be meaningful. Unfortunately, it isn't.
I'm going to try some other ways to fix it and keep you up to date.
Update 2: Final solution, guaranteed inelegant and working:
private Session getSession() throws Exception {
try {
ChannelExec testChannel = (ChannelExec) session.openChannel("exec");
testChannel.setCommand("true");
testChannel.connect();
if(logger.isDebugEnabled()) {
logger.debug("Session successfully tested, use it again.");
}
testChannel.exit();
} catch (Throwable t) {
logger.info("Session terminated. Create a new one.");
session = jsch.getSession(user, host, port);
session.setConfig(config);
session.connect();
}
return session;
}
This version runs several weeks in a productive environment. Once a day I have the info message logged.
The costs of opening a channel and performing some do-nothing-command are somewhat annoying, but I found no other way to be definitely sure about the state of the session.
You can try by invoking the following method before invoking Session#connect().
Session#setServerAliveInterval(int milliseconds)
Although I found one more function Session#sendKeepAliveMsg() which can be tried.
You can use a pool , I used org.apache.commons.pool2 so the pool is responsible of providing connected sessions, basically:
- Create JSCH Session on makeObject
- connect on activate if disconnected
- check if isConnected on validate
- sendKeepAliveMsg on passivate
Above worked for me, also keep in mind that if you add logic on validate, the poolConfig should set true on testOnBorrow or testOnReturn. So I used KeyedObjectPool you should get connections from the pool via borrowObject method and make sure you return them to the pool once you operation is complete via returnObject.
来源：https://stackoverflow.com/questions/16127200/jsch-how-to-keep-the-session-alive-and-up