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port scanning

 
Greenhorn
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i want to do port scanning in java
that i want to listen which ports are open ,closed or blocked
how can i do this using java?
 
Rancher
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You could try to open Socket connections to each port you're interested in. You probably want to make the code multi-threaded so you can open connections to many ports (or machines) at the same time, because it'll take a while for the connection attempts to time out if nothing is listening on that port.

Keep in mind that port scanning is considered a hostile (and possibly illegal) thing to do if you don't have permission to do it.

What do you mean by a "blocked" port?
 
author and iconoclast
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Java is a pretty poor choice for this, actually; ideally you'd want to send individual specially-crafted packets and look at the responses. Java won't give you that kind of control.
 
Consider Paul's rocket mass heater.
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