java.net.ConnectException: Connection refused

Question

I'm trying to implement a TCP connection, everything works fine from the server's side but when I run the client program (from client computer) I get the following error:

java.net.ConnectException: Connection refused
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351)
        at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432)
        at java.net.Socket.connect(Socket.java:529)
        at java.net.Socket.connect(Socket.java:478)
        at java.net.Socket.<init>(Socket.java:375)
        at java.net.Socket.<init>(Socket.java:189)
        at TCPClient.main(TCPClient.java:13)

I tried changing the socket number in case it was in use but to no avail, does anyone know what is causing this error & how to fix it.

The Server Code:

//TCPServer.java

import java.io.*;
import java.net.*;

class TCPServer {
    public static void main(String argv[]) throws Exception {
        String fromclient;
        String toclient;

        ServerSocket Server = new ServerSocket(5000);

        System.out.println("TCPServer Waiting for client on port 5000");

        while (true) {
            Socket connected = Server.accept();
            System.out.println(" THE CLIENT" + " " + connected.getInetAddress()
                    + ":" + connected.getPort() + " IS CONNECTED ");

            BufferedReader inFromUser = new BufferedReader(
                    new InputStreamReader(System.in));

            BufferedReader inFromClient = new BufferedReader(
                    new InputStreamReader(connected.getInputStream()));

            PrintWriter outToClient = new PrintWriter(
                    connected.getOutputStream(), true);

            while (true) {

                System.out.println("SEND(Type Q or q to Quit):");
                toclient = inFromUser.readLine();

                if (toclient.equals("q") || toclient.equals("Q")) {
                    outToClient.println(toclient);
                    connected.close();
                    break;
                } else {
                    outToClient.println(toclient);
                }

                fromclient = inFromClient.readLine();

                if (fromclient.equals("q") || fromclient.equals("Q")) {
                    connected.close();
                    break;
                } else {
                    System.out.println("RECIEVED:" + fromclient);
                }

            }

        }
    }
}

The Client Code:

//TCPClient.java

import java.io.*;
import java.net.*;

class TCPClient {
    public static void main(String argv[]) throws Exception {
        String FromServer;
        String ToServer;

        Socket clientSocket = new Socket("localhost", 5000);

        BufferedReader inFromUser = new BufferedReader(new InputStreamReader(
                System.in));

        PrintWriter outToServer = new PrintWriter(
                clientSocket.getOutputStream(), true);

        BufferedReader inFromServer = new BufferedReader(new InputStreamReader(
                clientSocket.getInputStream()));

        while (true) {

            FromServer = inFromServer.readLine();

            if (FromServer.equals("q") || FromServer.equals("Q")) {
                clientSocket.close();
                break;
            } else {
                System.out.println("RECIEVED:" + FromServer);
                System.out.println("SEND(Type Q or q to Quit):");

                ToServer = inFromUser.readLine();

                if (ToServer.equals("Q") || ToServer.equals("q")) {
                    outToServer.println(ToServer);
                    clientSocket.close();
                    break;
                } else {
                    outToServer.println(ToServer);
                }
            }
        }
    }
}

Hatcher

Can you please post the client code? If it is a remote client make sure you don't have any firewall issues! – Tompkins

I turned off firewalls on both client & server & still same problem – Hatcher

What interface is the server listening on. If you are only listening on localhost, you cannot connect remotely. – Sheenasheeny

I was trying to connect remotely while using localhost, face palm. This is my first trial with TCP >.< How do I make it work remotely? – Hatcher

Remember that you may have some 'bare metal' hardware firewalls in between as well... does it work if client and server are on the same box? – Tompkins

same box as in same machine? If so yes – Hatcher

I tried your code out and I didn't have any problems on my machine. it has to be something blocking your connection or else you are starting them in the wrong order. Are you making sure that your server isn't getting closed when you start the client up. My process was this. put both class file in one directory, then opened 2 command prompts to that directory to execute them separately. if your using an IDE it may be closing the server automatically which is why i recommend doing it this way – Computation

Server Fault has a canonical question about Connection Refused. – Cymbre

Answer 1

This exception means that there is no service listening on the IP/port you are trying to connect to:

• You are trying to connect to the wrong IP/Host or port.
• You have not started your server.
• Your server is not listening for connections.
• On Windows servers, the listen backlog queue is full.

Cocytus

Just to make the point clear - "Java core is just fine". Only problem is we overlook issues.. (server state, ipaddress, port, internet connectivity - being on the same router is must for local IP's and more) – Sulphate

Collin, what exactly do you mean by 'the server is not waiting to accept connections'? People are parroting this around as though it means something. – Appal

I wrote this a while ago but I think I meant it as another way of saying you have not started your server. – Cocytus

in my case I had four Gennymotion simulators running and I was trying to load the app on Galaxy tab and I was getting this error. after reading a lot from the buddy WEB, I then closed out all the simulators and eclipse, killed the ADP in the task manager and then restarted the Eclipse and everything is started working properly. I think when you have multiple simulators running and then you try to connect device, the ADB goes nuts in my experience. those are my two cents... :) – Pagandom

I am getting this exception while trying to connect to a soap service. java.util.concurrent.ExecutionException: java.net.ConnectException: https://services.xxxxxxxxx.com/xxxxxxxxxv2/Service.svc/soap. It is not connection refused or timed out. It just prints out the address of the API and blows up. I have no idea whats causing this. – Oscitancy

In case you are spring boot < 1.4, check if you activated WebIntegrationTest ... did the trick for me – Haunting

@Sabarish Kumaran.V Your edit was (a) irrelevant and (b) wrong. Don't do that. – Appal

@CollinPrice when app closed by clear ram, for the next time I got connection refused. do you have any idea? – Labdanum

Add "OpenVPN Connect needs to be restarted" to the list of possible causes... – Hume

Answer 2

I would check:

• Host name and port you're trying to connect to
• The server side has managed to start listening correctly
• There's no firewall blocking the connection

The simplest starting point is probably to try to connect manually from the client machine using telnet or Putty. If that succeeds, then the problem is in your client code. If it doesn't, you need to work out why it hasn't. Wireshark may help you on this front.

Benavidez

I get this exception sometimes. This happens for a particular period of time. It immediately throws this exception. And then everything becomes fine. I have a firewall in the server. But I have added an inbound rule to allow incoming connections on port 8080. Is the rule ignored sometimes? – Prau

@Ashwin: It's impossible to say, really - you'd need to work out exactly how far the data's getting. Look at your firewall logs etc. – Benavidez

@JonSkeet how to config our firewall if we have this error? – Reconcile

@Nikhil: I'm not qualified to answer that, but I suspect anyone who is qualified would need a lot more information to be able to help you. (For one thing, we don't know what firewall you have...) – Benavidez

Answer 3

One point that I would like to add to the answers above is my experience-

"I hosted on my server on localhost and was trying to connect to it through an android emulator by specifying proper URL like http://localhost/my_api/login.php . And I was getting connection refused error"

Point to note - When I just went to browser on the PC and use the same URL (http://localhost/my_api/login.php) I was getting correct response

so the Problem in my case was the term localhost which I replaced with the IP for my server (as your server is hosted on your machine) which made it reachable from my emulator on the same PC.

---

To get IP for your local machine, you can use ipconfig command on cmd you will get IPv4 something like 192.68.xx.yy Voila ..that's your machine's IP where you have your server hosted. use it then instead of localhost

http://192.168.72.66/my_api/login.php

---

Note - you won't be able to reach this private IP from any node outside this computer. (In case you need ,you can use Ngnix for that)

Dear

Answer 4

You have to connect your client socket to the remote ServerSocket. Instead of

Socket clientSocket = new Socket("localhost", 5000);

do

Socket clientSocket = new Socket(serverName, 5000);

The client must connect to serverName which should match the name or IP of the box on which your ServerSocket was instantiated (the name must be reachable from the client machine). BTW: It's not the name that is important, it's all about IP addresses...

Tompkins

I assume she is running them both on the same machine for testing purposes which is why localhost would be fine to use – Computation

@Aaron: She said it works if client and server run on the same machine (you can find the answer in another comment). – Tompkins

'The above row binds the socket to localhost' No it doesn't, it binds it to INADDR_ANY. That allows it to accept connections via any NIC. What the OP is doing is already correct. Answer is completely incorrect. Downvoting. – Appal

@EJP: You're right with the ServerSocket, I modified the answer. Nevertheless, the clientSocket still tries to connect to localhost. – Tompkins

@Tompkins You need to remove the phrase about the bind address. – Appal

@Tompkins bind() binds the socket to a local NIC and port. connect() connects you to a remote IP:port. They are completely different operations. – Appal

Answer 5

I had the same problem, but running the Server before running the Client fixed it.

Looksee

Of course you have to run the server before the client. Running the client first and trying to connect to the server means you're connecting to nothing when you fire up your server. – Abydos

@Abydos Yes it was obvious but it wasn't too obvious for some new programmers (like myself 3 years ago) so I just wanted to share it with those fellows who were clueless like me. – Looksee

Thanks, it also helped me, the test connection was succesfull but couldn't show any tables data. – Voracious

Answer 6

I had the same problem with Mqtt broker called vernemq.but solved it by adding the following.

1. $ sudo vmq-admin listener show

to show the list o allowed ips and ports for vernemq

1. $ sudo vmq-admin listener start port=1885 -a 0.0.0.0 --mountpoint /appname --nr_of_acceptors=10 --max_connections=20000

to add any ip and your new port. now u should be able to connect without any problem.

Hope it solves your problem.

Kurt

This saved my day, but since vernemq does not install with apt-get, some people will need this link: vernemq.com/docs/installation/debian_and_ubuntu.html – Odontoid

Answer 7

Hope my experience may be useful to someone. I faced the problem with the same exception stack trace and I couldn't understand what the issue was. The Database server which I was trying to connect was running and the port was open and was accepting connections.

The issue was with internet connection. The internet connection that I was using was not allowed to connect to the corresponding server. When I changed the connection details, the issue got resolved.

Antinode

Answer 8

i got this error because I closed ServerSocket inside a for loop that try to accept number of clients inside it (I did not finished accepting all clints)

so be careful where to close your Socket

Alkahest

Answer 9

In my case, I gave the socket the name of the server (in my case "raspberrypi"), and instead an IPv4 address made it, or to specify, IPv6 was broken (the name resolved to an IPv6)

Gereld

Answer 10

In my case, I had to put a check mark near Expose daemon on tcp://localhost:2375 without TLS in docker setting (on the right side of the task bar, right click on docker, select setting)

Talanta

Answer 11

I changed my DNS network and it fixed the problem

Daisey

Answer 12

I saw the same error message ""java.net.ConnectException: Connection refused" in SQuirreLSQL when it was trying to connect to a postgresql database through an ssh tunnel.

Example of opening tunel:

Example of error in Squirrel with Postgresql:

It was trying to connect to the wrong port. After entering the correct port, the process execution was successful.

See more options to fix this error at: https://mcmap.net/q/115952/-java-net-connectexception-connection-refused

Necessaries

Answer 13

For those who are experiencing the same problem and use Spring framework, I would suggest to check an http connection provider configuration. I mean RestTemplate, WebClient, etc.

In my case there was a problem with configured RestTemplate (it's just an example):

public RestTemplate localRestTemplate() {
   Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("localhost", <some port>));
   SimpleClientHttpRequestFactory clientHttpReq = new SimpleClientHttpRequestFactory();
   clientHttpReq.setProxy(proxy);
   return new RestTemplate(clientHttpReq);
}

I just simplified configuration to:

public RestTemplate restTemplate() {
   return new RestTemplate(new SimpleClientHttpRequestFactory());
}

And it started to work properly.

Fiddlededee

Answer 14

I had same problem and the problem was that I was not closing socket object.After using socket.close(); problem solved. This code works for me.

ClientDemo.java

public class ClientDemo {
    public static void main(String[] args) throws UnknownHostException,
            IOException {
        Socket socket = new Socket("127.0.0.1", 55286);
        OutputStreamWriter os = new OutputStreamWriter(socket.getOutputStream());
        os.write("Santosh Karna");
        os.flush();
        socket.close();
    }
}

and ServerDemo.java

public class ServerDemo {
    public static void main(String[] args) throws IOException {
        System.out.println("server is started");
        ServerSocket serverSocket= new ServerSocket(55286);
        System.out.println("server is waiting");
        Socket socket=serverSocket.accept();
        System.out.println("Client connected");
        BufferedReader reader=new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String str=reader.readLine();
        System.out.println("Client data: "+str);
        socket.close();
        serverSocket.close();

    }
}

Hussein

Not closing the client socket does not cause a connection refusal. There wouldn't be a client socket to close if the connection had been refused. – Appal

Answer 15

In my case, with server written in c# and client written in Java, I resolved it by specifying hostname as 'localhost' in the server, and '[::1]' in the client. I don't know why that is, but specifying 'localhost' in the client did not work. Supposedly these are synonyms in many ways, but apparently, not not a 100% match. Hope it helps someone avoid a headache.

Buroker

Answer 16

If you use intellij and you encounter the same error, check if you don't have a method breakpoint enabled somewhere. It worked for me :)

Pratincole

Answer 17

You probably didn't initialize the server or client is trying to connect to wrong ip/port.

Unkindly

Answer 18

There is a service called MySQL80 that should be running to connect to the database

for windows you can access it by searching for services than look for MySQL80 service and make sure it is running

Francinafrancine