Java sockets, echo server

Question

I'm trying to do a very basic echo server using java sockets, it works perfectly locally(running both the server and client on the same computer), when I try to run the client from another computer i get the exception :

Couldn't get I/O for the connection to XXX.XXX.XX.X

XXX.XXX.XX.X being the IP of the machine on which the server is running

btw : my code for both the server and the client is roughly that of the oracle beginner tutorials : server client

EDIT : The full stacktrace I get :

java.net.ConnectException: Connection timed out: connect at java.net.DualStackPlainSocketImpl.connect0(Native Method) at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source) at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source) at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source) at java.net.AbstractPlainSocketImpl.connect(Unknown Source) at java.net.PlainSocketImpl.connect(Unknown Source) at java.net.SocksSocketImpl.connect(Unknown Source) at java.net.Socket.connect(Unknown Source) at java.net.Socket.connect(Unknown Source) at java.net.Socket.<init>(Unknown Source) at java.net.Socket.<init>(Unknown Source) at sockets.Client.main(Client.java:16)

Can you ping the server machine from the client machine at all? — RealSkeptic, Oct 26 '15 at 19:47
Correct me if i'm wrong, but i think that exception is thrown after the socket gets connected, when he tries to get the input and output stream. So the port should be open. — Marcello Davi, Oct 26 '15 at 19:48
no it never gets to the input and output stream ( just verified now) — isco, Oct 26 '15 at 19:50
You could print the stacktrace (inside the catch-block of the IOException) to get more details concerning the problem. — Stefan Freitag, Oct 26 '15 at 19:53
I know it might sound obvious... but are you running the server before running the client? — Marcello Davi, Oct 26 '15 at 20:01
there is a link in the question, i use exactly the code of oracle except that I set the port number and ip adresse in the code instead of giving them to the main method via args — isco, Oct 26 '15 at 20:08
You could check the EchoServer without the EchoClient. Assuming that the EchoServer runs on the remote machine, you could use the telnet command instead of the EchoClient, i.e. `telnet remoteIp remotePort`. — Stefan Freitag, Oct 26 '15 at 20:22

score 0 · Answer 1 · edited May 23 '17 at 11:58

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As mentioned in the comments, the two used computers were hooked on two different wifi suppliers. An answer to a similar question mentions possible other reasons.

edited May 23 '17 at 11:58

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answered Oct 26 '15 at 20:30

Stefan Freitag

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score 0 · Accepted Answer · answered Oct 27 '15 at 09:10

I get the exception

    Couldn't get I/O for the connection to XXX.XXX.XXX.XXX

That is not an exception. It is a poorly designed error message that conceals the exception. When you get an exception, don't display/print/log a meaningless error message of your own devising. Display/print/log the exception itself, and its message, and its class, and its stacktrace.

EDIT: The full stacktrace I get:

    java.net.ConnectException: Connection timed out: connect

Exactly. This is the real exception, and it almost certainly means there is a firewall preventing you from making the required connection.

Java sockets, echo server

2 Answers2