UnknownHostException: name or service not known

Question

I\'m attempting to return some data from an API using OkHttpClient in com.squareup.okhttp. I\'ve run into a few errors that i have eventually been able to overcome but i can\'t

Answer 1

For error like "java.net.UnknownHostException: [hostname]"

The reason is your hostname is not in /etc/hosts, The solution is simple:

sudo vim /etc/hosts

change the line looks like:

127.0.0.1  localhost

to:

127.0.0.1  [hostname] localhost

Save and exit. If the problem still exist, may be you need to restart or run :

sudo ifconfig eth0 down&&sudo ifconfig eth0 up

Hope it can help you!

Answer 2

Since you have not posted your code that how your connect() called, so please refer to my following working code

    private class StringRequest extends AsyncTask<Void, Void, String> {
        @Override
        protected String doInBackground(Void... voids) {
            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder()
                    .url("https://socialweb-analytics.lcloud.com/api/public/reports/jobs?companyKey=ato")
                    .addHeader("authorization", "Basic c2RidXNpbmVzc2FuYWx5dGljc0BhdG8uZ292LmF1OkFuYWx5dGljezEh")
                    .addHeader("cache-control", "no-cache")
                    .addHeader("postman-token", "65ef5553-77b5-053f-9c01-4fdf76bdc92f")
                    .build();
            try {
                Response response = client.newCall(request).execute();
                return response.body().string();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }
        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            System.out.println(s);
        }
    }

Then inside onCreate:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    mTextView = (TextView) findViewById(R.id.textView);
    new StringRequest().execute();
}

My app run and got the following result (perhaps because of expired/invalid token):

I/System.out: {"code":500,"message":"There was an error processing your request. It has been logged (ID a2f28b587b2f9dcc)."}

P/S: make sure you have set <uses-permission android:name="android.permission.INTERNET" /> inside AndroidManifest.xml file

Answer 3

Expanding on zhenbo xu's great answer this is what I did to automate things with sed in EC2.

sudo sed -i -e '/127.0.0.1/ s/\(localhost\)/'$(hostname)' \1/' /etc/hosts

Note that to allow variable expansion the single quotes end and restart around the subshell call.

hostname is an executable on some Linux systems (but maybe not all, so you can use an environment variable instead,or remove the quotes around the subshell and use static string).

The \1 is sed magic, it puts the "captured" search string (s/search/replacement/) in the escaped parentheses back into the replacement string.