import android.util.Log;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

public class Parse {
    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = null;
    public Parse(){

    }
    public static String getJSONFromUrl(String url) throws IOException {
        Log.e("URL",url);
        try{
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url);
            HttpResponse httpResponse = httpClient.execute(httpPost);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();

        }catch (UnsupportedEncodingException e){
            Log.e("JSON Parser", "UnsupportedEncodingException " + e.toString());
            e.printStackTrace();
        }catch (ClientProtocolException e){
            Log.e("JSON Parser", "ClientProtocolException " + e.toString());
            e.printStackTrace();
        }catch (IOException e){
            Log.e("JSON Parser", "IOException " + e.toString());
            e.printStackTrace();
        }
        try{
            BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while((line = reader.readLine())!= null){
                sb.append(line + "\n");

            }
            is.close();
            json = sb.toString();

        }catch (Exception e){
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }
        return json;
    }

import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;

public class Havadurumu extends AppCompatActivity {
    TextView txt_derece;
    Button btn_goster;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_havadurumu);
        txt_derece = (TextView) findViewById(R.id.txtgoster);
        btn_goster = (Button) findViewById(R.id.btn_hava);

        btn_goster.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                new getWeatherCondition().execute();
            }
        });

    }
    private class getWeatherCondition extends AsyncTask<Void,Void,Void>{
        String dolar;
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
        @Override
        protected Void doInBackground(Void... Params)  {
            String url = "http://www.doviz.gen.tr/doviz_json.asp?version=1.0.4";
            JSONObject jsonObject = null;
            try {
                String json =  Parse.getJSONFromUrl(url);
                try {
                    jsonObject = new JSONObject(json);
                } catch (JSONException e) {
                    e.printStackTrace();
                }
                try {
                    dolar = jsonObject.getString("sonkayit");
                } catch (JSONException e) {
                    e.printStackTrace();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;

        }
        @Override
        protected void onPostExecute(Void args) {
            txt_derece.setText(dolar);
        }
    }

}

Merhaba arkadaşlar böyle bir şeyler çıktı ortaya çalışıyor ama sizce ne kadar verimlidir ve hızlıdır. Tavsiyelerinizi bekliyorum