java.net.ConnectException: Connection refused:
connect is one of the most common networking exception in Java. This error comes
when you are working with client-server architecture and trying to make TCP
connection from client to server. Though this is not as cryptic as java.lang.OutOfMemoryError: Java heap
Space or java.lang.UnsupportedClassVersionError,
it’s still a frequent problem in distributed Java applications. java.net.ConnectException:
Connection refused: connect also comes in case of RMI (Remote Method
Invocation), because RMI also use TCP IP protocol underneath. While writing
client socket code in Java, You should always provide proper handling of this exception. In this Java
tutorial, we will see why connection refused exception comes and how to
solve java.net.ConnectException: Connection refused: connect Exception
in Java.
java.net.ConnectException: Connection refused Error – Possible reasons
Connection refused is a clear case of client trying to connect on a TCP
port but not able to succeed. Here are some of the possible reason why java.net.ConnectException:
Connection refused: connect comes:
1) Client
and Server, either or both of them are not in network.
Yes its possible that they are not connected to LAN or internet or any
other network in that case Java will throw
"java.net.ConnectException: Connection refused"
exception on client side.
2) Server
is not running
Second most common reason is server is down and not running. In that case
also you will get java.net.ConnectException: Connection refused error. What I
don't like is that the message it gives, no matter what is the reason it print
same error. By the way you can use following networking commands e.g. ping
to check if server is running and listening on port.
3) Server
is running but not listening on port, client is trying to connect.
This is another common cause of "java.net.ConnectException:
Connection refused", where server is running but listening on
different port. It’s hard to figure out this case, until, you think about it
and verify configuration. If you
are working on large project and have hierarchical configuration file, Its
possible that either default configuration
is taking place or some other settings is overriding your correct
setting.
4)
Firewall is not permitted for host-port combination
Almost every corporate network is protected by firewalls. If you are
connecting to some other companies network e.g. opening a FIX session to broker, in any
Electronic Trading System, than you need to raise firewall
request from both side to ensure that they permit each others IP address and port number. If
firewall is not allowing
connection than also you will receive same java.net.ConnectException:
Connection refused exception in Java application.
5) Host
Port combination is incorrect.
This could be another reason of java.net.ConnectException:
Connection refused: connect .It’s quite possible that either you are
providing incorrect host port combination or earlier host port combination has
been changed on server side. Check latest configuration on both client and
server side to avoid connection refused exception.
6)
Incorrect protocol in Connection String
TCP is underlying protocol for many high level protocol including HTTP, RMI
and others. While passing connection
string you need to ensure that you are passing correct protocol, which
server is expecting e.g. if server has exposed
its service via RMI than connection string should begin with rmi://
How to solve java.net.ConnectException: Connection refused
Simple solution is to find out the actual reason of java.net.ConnectException:
Connection refused, Possibly one of the reasons mentioned above and solve
that. What is most important here is approach of finding correct cause and
solution. Here are some tips which may help you to identify real cause of java.net.ConnectException:
Connection refused :
1) First try to ping destination host , if
host is ping-able it means client and server machine are in network.
2) Try connecting to server host and port using telnet. If you are able to
connect means something is wrong with your client code. Also by observing
telnet output you will come to know whether server is running or not or server
is disconnecting the connection.
That’s all on What is java.net.ConnectException: Connection refused:
connect error in Java and how to fix it. As I said there is no definite
reason for this error and could be many things which can go wrong. Thankfully,
this is more to do with configuration or environment and once you find out
real cause, you might not even need to make any change on your side.
Related Java debugging tutorials for Java programmers
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