I'm trying to connect to server socket in java using my router's public ip,
first, I tried by simply configuring server socket to localhost, like this,
server = new ServerSocket(5000);
It is working on localhost but not working on trying internal ip 192.168.1.6
then, I tried configuring server socket to the internal Ip (saw this solution), code is as follows,
int backlog = 5;
server = new ServerSocket(5000, backlog, InetAddress.getByName("192.168.1.6"));
and it is working as my devices are connected to same network, I can connect to this Ip 192.168.1.6 from a device with Ip 192.168.1.5 on the same network but when I use public ip of my router from client side, connection is getting timed out, I've done port forwarding,
What am I doing wrong here? any help is appreciated, thanks in advance.
EDIT :
I came to about NAT-loopback (saw this solution) as I was trying to connect using public ip while being on same network so I tried different network but still it is not connecting, connection is getting timed out.
Firstly replace your port number by 8080, which is the default port for HTTP when you are not root. Then you have to open the port 8080 on your router to allow the client to connect.
Your server must be connected to the Internet and have a public IP address. Then the client can connect to this public IP address.
I am getting BindException exception while reusing same Address.Following is my code.
in openConnection method :
69. Selector selector = SelectorProvider.provider().openSelector();
70. SocketChannel socketChannel = SocketChannel.open();
71. socketChannel.bind(new InetSocketAddress(port));// Edited
72. socketChannel.socket().setReuseAddress(true);
73. socketChannel.configureBlocking(false);
74. socketChannel.connect(remoteAddress);
Exception:
java.net.BindException: Address already in use
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:414)
at sun.nio.ch.Net.bind(Net.java:406)
at sun.nio.ch.SocketChannelImpl.bind(SocketChannelImpl.java:580)
at sun.nio.ch.SocketAdaptor.bind(SocketAdaptor.java:135)
at com.example.client.request.Client.openConnection(Client.java:72)
Edit
I solved InvalidArgument exception and I have edited the post above but now while reconnecting on same port I get the above exception.Is some thing I am doing wrong?
If you want to reuse an address you have to call setReuseAddress(true) before binding the socket.
Signals that an error occurred while attempting to bind a socket to a local address and port. Typically, the port is in use, or the requested local address could not be assigned.
When you start a web server or application server, which typically listen on a port e.g. Tomcat or Jetty listens on 8080 and 8084 for HTTP and HTTPS traffic, they bind a socket to a local address and port. If you give them hostname e.g. localhost or devhost, then they used /etc/host in both Windows and Linux to resolve domain name into IP address, if this mapping is incorrect than you will get java.net.BindException: Cannot assign requested address: JVM_Bind. This host to IP address mapping file can be found at C:\Windows\System32\Drivers\etc\hosts, where C:\Windows is where you have installed windows operating system. If you look at this file, you will see it contains IP address and hostname as shown below :
127.0.0.1 localhost
192.168.52.1 localhost
Just, correct the mapping, or add 127.0.0.1 against localhost to resolve this issue
I'm running a socket on my Mac laptop and when I telnet the IP address of my computer it says (IP is hidden for security reasons):
telnet 7-.---.--.--- 4005
Trying 7-.---.--.---...
telnet: connect to address 7-.---.--.---: Connection refused
telnet: Unable to connect to remote host
However when I do telnet on "localhost" it works it says (did not hide any info this is the raw message):
Trying ::1...
telnet: connect to address ::1: Connection refused
Trying fe80::1...
telnet: connect to address fe80::1: Connection refused
Trying 127.0.0.1...
Connected to localhost.
Update - Opened Firewall
Now after opening all of the ports localhost still works the same way as before however when I try the raw IP I get this new error:
Trying 7-.---.--.---...
telnet: connect to address 7-.---.--.---: Operation timed out
telnet: Unable to connect to remote host
The server is listening on the loopback interface only (INADDR_LOOPBACK), not all interfaces (INADDR_ANY) or a firewall is interfering with the connection.
Probably a firewall: generally localhost is not barred, but the external IP interface is.
What are the steps I should take to solve the error:
java.net.UnknownHostException: Invalid hostname for server: local
I added the new virtual host name at Android emulator but the result returns to
java.net.UnknownHostException virtualhostname at
java.net.InetAddress.lookUpHostByName(InetAddress.java:506)
When I type my virtualhost URL on my PC, it works on display. Then again, when I ran on Emulator and check on Logcat, I couldn't be able to read or check the HTTP status if 200, 202, or an error code number. It simply returned to UnknownHostException
I was having the same issue on my mac. I found the issue when I pinged my $HOSTNAME from terminal and it returned ping: cannot resolve myHostName: Unknown host.
To resolve:
Do echo $HOSTNAME on your terminal.
Whatever hostname it shows (lets say myHostName), try to ping it : ping myHostName. If it returns ping: cannot resolve myHostName: Unknown host then add an entry into your /etc/hosts file.
For that edit /etc/hosts file and add following:
127.0.0.1 myHostName
What the exception is really saying is that there is no known server with the name "local". My guess is that you're trying to connect to your local computer. Try with the hostname "localhost" instead, or perhaps 127.0.0.1 or ::1 (the last one is IPv6).
From the javadocs:
Thrown to indicate that the IP address
of a host could not be determined.
127.0.0.1or ::1 or "localhost" should always be the loopback interface, so if that doesn't work I'd be really surprised.
If there really is a server called "local" on your network - examine your DNS settings or add it to your hosts file.
java.net.UnknownHostException: Host is unresolved:
Thrown to indicate that the IP address of a host could not be determined.
This exception is also raised when you are connected to a valid wifi but router does not receive the internet. Its very easy to reproduce this:
Connect to a valid wifi
Now remove the cable from the router while router is pluged-in
You will observe this error!!
You can't really solve this, You can only notify the user gracefully. (something like - "Unable to make a connection")
This is not specific to the question, but this question showed up when I was Googling for the mentioned UnknownHostException, and the fix is not found anywhere else so I thought I'd add an answer here.
The exception that was continuously received was:
java.net.UnknownHostException: google.com
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at java.net.Socket.<init>(Socket.java:434)
at java.net.Socket.<init>(Socket.java:211)
...
No matter how I tried to connect to any valid host, printing it in the terminal would not help either. Everything was right.
The Solution
Not calling trim() for the host string which contained whitespace. In writing a proxy server the host was obtained from HTTP headers with the use of split(":") by semicolons for the HOST header. This left whitespace, and causes the UnknownHostException as a host with whitespace is not a valid host. Doing a host = host.trim() on the String host solved the ambiguous issue.
Your hostname is missing. JBoss uses this environment variable ($HOSTNAME) when it connects to the server.
[root#xyz ~]# echo $HOSTNAME
xyz
[root#xyz ~]# ping $HOSTNAME
ping: unknown host xyz
[root#xyz ~]# hostname -f
hostname: Unknown host
There are dozens of things that can cause this. Please comment if you discover a new reason.
For a hack until you can permanently resolve this issue on your server, you can add a line to the end of your /etc/hosts file:
127.0.0.1 xyz.xxx.xxx.edu xyz
This might happen due to various reasons
1) Check if you have VPN connected, you might get this error sometimes if yes
"Your hostname, localhost resolves to a loopback address: 127.0.0.1; using 10.xxx.1.193 instead (on interface cscotun0)"
2) Check your $HOSTNAME
3) try to ping $HOSTNAME on commandline and if it doesnt work, tweak the system settings to make your local host respond to pings
Try the following :
String url = "http://www.google.com/search?q=java";
URL urlObj = (URL)new URL(url.trim());
HttpURLConnection httpConn =
(HttpURLConnection)urlObj.openConnection();
httpConn.setRequestMethod("GET");
Integer rescode = httpConn.getResponseCode();
System.out.println(rescode);
Trim() the URL
Trying to connect to your local computer.try with the hostname "localhost" instead or perhaps ::/ - the last one is ipv6
Please try to set SPARK_LOCAL_IP environment variable to the ip address(can be localhost i.e. your own ip address) you want to connect. E.g.
$ export SPARK_LOCAL_IP=182.95.208.152
This way you will not be required to alter existing linux settings.
Worked for me, hope helps you too.
Connect your mobile with different wifi connection with different service provider.
I don't know the exact issue but i could not connect to server with a specific service provider but it work when i connected to other service provider. So try it!
I had this issue in my android app when grabbing an xml file the format of my link was not valid, I reformatted with the full url and it worked.
If you are here because your emulator gives you that Exception, Go to Tools > AVD Manager in your android emulator and Cold boot your Emulator.
I had the same issue.
Restart docker was the fix for me. For some reason it needed a restart, I don´t know why, but it worked.
If your /etc/localhosts file has entry as below:
Add hostname entry as below:
127.0.0.1 local host (add your hostname here)
::1 (add hostname here) (the last one is IPv6).
This should resolve the issue.
i tried this code:
http://programming-guides.com/java/tcp-client-server-chat
(full example)
and it's working but when i switch the "host" int the client side to an external IP (insted of localhost) it give me this error:
"Cannot get IO for connection to.."
i treid to switch the port but it didnt work..
Is the server running on that remote machine? Is the port open in the firewall?
Try to netcat to the remote host. If you get an connection the example maybe wrong. If not, you cannot connect to that host: host not exists, not listen on that port, port is filtered, etc, etc.