Android Advertising ID を取得する ref: http://qiita.com/f_nishio/items/e3665a93b6e061f9ea0f

MainActivity.java

package jp.gr.java_conf.fofn.advertisingid;

import android.app.Activity;
import android.content.Context;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

import com.google.android.gms.ads.identifier.AdvertisingIdClient;
import com.google.android.gms.common.GooglePlayServicesNotAvailableException;
import com.google.android.gms.common.GooglePlayServicesRepairableException;

import java.io.IOException;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "AdvertisingId";

    class AdIdTask extends AsyncTask<Void, Void, String> {
        private Activity mActivity;

        AdIdTask(Activity activity) {
            mActivity = activity;
        }

        @Override
        protected String doInBackground(Void... params) {
            String advertisingId = "";
            try {
                AdvertisingIdClient.Info info =
                        AdvertisingIdClient.getAdvertisingIdInfo(mActivity.getApplicationContext());
                advertisingId = info.getId();
            } catch (GooglePlayServicesNotAvailableException e) {
                Log.e(TAG, "GooglePlayServices not available.");
            } catch (GooglePlayServicesRepairableException e) {
                //
            } catch (IOException e) {
                //
            }
            return advertisingId;
        }

        @Override
        protected void onPostExecute(String id) {
            TextView view = (TextView)mActivity.findViewById(R.id.adid);
            view.append(id);
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // AdvertisingIdClient cannot be called in the main thread.
        AsyncTask<Void, Void, String> task = new AdIdTask(this);
        task.execute();
    }
}