[java] java.net.UnknownHostException: Invalid hostname for server: local

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

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!

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:

1. Connect to a valid wifi
2. 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")

Trying to connect to your local computer.try with the hostname "localhost" instead or perhaps ::/ - the last one is ipv6

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

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.

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.

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

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 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:

1. Do echo $HOSTNAME on your terminal.
2. 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.

3. For that edit /etc/hosts file and add following:

   127.0.0.1 myHostName

Hope it helps.

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.

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