如何检查惠特指定端口是否可以通信？

Question

I am using Java Secure Channel to connect with hosts in a network. I am using following code:

int port = 22;JSch jsch = new JSch();
try {
session=jsch.getSession(username,hostname,port);
}
catch (JSch Exception e1){
e1.printStackTrace();
}
session.setPassword("mypassword");
try {
session.connect();
}catch (JSchException e1){
System.out.println("Did not connect");
return;
}

By using this code I am able to connect to host. But if host is unavailable/offline then I have to wait for JSchException.

1) I want to first check whether host is available for communication or not and if available then only try to connect.

2) Also I want to set timeout for connection,if connection doesn't established within that time interval must give exception.

How to check if host is available? and set timeout for connection?

Answer 1

Testing before connecting makes no big sense, as port can become unavailable right after test. Try to use session.setTimeout() to set timeout in millis.

Answer 2

How to check whether specified port is available for communication?

How to check whether specified X is available for Y:

Try to use it for Y. It's an infallible test. Any other technique has timing-window problems.