使用Java的HttpURLConnection无法从Flickr API返回结果

Question

I'm having problems querying Flickr REST API for searching photos:

https://www.flickr.com/services/api/explore/flickr.photos.search

I'm writing a small test app in Android using HttpURLConnection and I do not want to use any frameworks (such as OkHttp etc.) as this is just simple learning exercise.

The problem that I am having is that although my HttpURLConnection returns a 200, there is no JSON response . But when I take the constructed REST URL from my logs, for example:

https://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=API_KEY&tags=basketball&format=json&nojsoncallback=1&api_sig=API_SIG

and copypaste it to a browser, I can see proper JSON.

This is A snippet of the JSON that the browser returns:

{"photos":{"page":1,"pages":2614,"perpage":100,"total":"261380","photo":[{"id":"39168832065","owner":"23023080@N02","secret":"1fb9ee772a","server":"4615","farm":5,"title":"_MG_2714_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194325488","owner":"23023080@N02","secret":"3bc00e37ee","server":"4656","farm":5,"title":"_MG_2719_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"39168829925","owner":"23023080@N02","secret":"15580858ce","server":"4695","farm":5,"title":"_MG_2723_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194323798","owner":"23023080@N02","secret":"c5e445bd6e","server":"4743","farm":5,"title":"_MG_2727_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"39168828415","owner":"23023080@N02","secret":"89b54b28bc","server":"4648","farm":5,"title":"_MG_2729_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194322658","owner":"23023080@N02","secret":"7eff365389","server":"4648","farm":5,"title":"_MG_2732_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"39168826725","owner":"23023080@N02","secret":"2eda660b60","server":"4723","farm":5,"title":"_MG_2734_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194321108","owner":"23023080@N02","secret":"0c794e38a8","server":"4765","farm":5,"title":"_MG_2735_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"40034887842","owner":"23023080@N02","secret":"6269997f0f","server":"4755","farm":5,"title":"_MG_2737_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194319778","owner":"23023080@N02","secret":"32991c9151","server":"4763","farm":5,"title":"_MG_2739_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194319168","owner":"23023080@N02","secret":"4dd5555f5c","server":"4709","farm":5,"title":"_MG_2746_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"40034885802","owner":"23023080@N02","secret":"3f9c5031db","server":"4671","farm":5,"title":"_MG_2747_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"26194317818","owner":"23023080@N02","secret":"e20b503f8f","server":"4668","farm":5,"title":"_MG_2757_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"40067785161","owner":"23023080@N02","secret":"4ab87667fd","server":"4612","farm":5,"title":"_MG_2760_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"40034884132","owner":"23023080@N02","secret":"235b7dc32d","server":"4744","farm":5,"title":"_MG_2762_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"40067784231","owner":"23023080@N02","secret":"0bbae58322","server":"4622","farm":5,"title":"_MG_2763_edit","ispublic":1,"isfriend":0,"isfamily":0},{"id":"40034882942","owner":"23023080@N02","secret":"30345b6b7b","server":"4626","farm":5,"title":"_MG_2764_edit","ispublic":1,"isfriend":0,"isfamily":0},

Why is the code not getting/reading the JSON from connection's input stream?

package com.bing.ary.xyz;

import android.os.AsyncTask;
import android.util.Log;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import javax.net.ssl.HttpsURLConnection;
import java.net.URL;


public class SearchFlickerAsync extends AsyncTask<String, Void, flikrPhotosResponse> {

        private static final String TAG = "SearchFlickerAsync";

        private String query;

        public SearchFlickerAsync(String query) {
        this.query = query;
        }

    public String getQuery() {
        return query;
        }

        public void setQuery(String query) {
        this.query = query;
        }

    @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected flikrPhotosResponse doInBackground(String... query) {

            Log.i(TAG,"doInBackground(), SearchFlickerAsync input param:"+query);

            HttpsURLConnection httpURLConnection = null;
            flikrPhotosResponse FlikrPhotosResponse = null;
            JsonElement jsonElemnt = null;
            JsonObject jsonObject = null;
            String queryUrl = null;
            StringBuilder queryBuilder = null;

            try {
                //create url string
                queryBuilder = new StringBuilder();
                queryBuilder.append(flickerApi.baseUrl);
                queryBuilder.append(flickerApi.searchFlicker);
                queryBuilder.append(flickerApi.flickrQuery_key + flickerApi.Key);
                queryBuilder.append(flickerApi.flickrQuery_tag);
                queryBuilder.append(this.query);
                queryBuilder.append("&format=json");
                queryBuilder.append("&nojsoncallback=1&api_sig=be97f5275f5a128fbe69dc2cde2560b9");
                //instantiate url for connection
                URL url = new URL(queryBuilder.toString());
                httpURLConnection = (HttpsURLConnection) url.openConnection();
                httpURLConnection.setRequestMethod("GET");
                httpURLConnection.setUseCaches(false);
                httpURLConnection.setAllowUserInteraction(false);
                httpURLConnection.setRequestProperty("Content-length", "0");
                httpURLConnection.connect();
                //no authorization token needed public API httpURLConnection.setRequestProperty("Authorization", "");
                Log.i(TAG,"doInBackground(), http request:"+url.toString());
                int status = httpURLConnection.getResponseCode();

                switch (status) {
                    case 200:
                    case 201:
                        Log.i(TAG,"doInBackground(), http response status:"+status);
                        BufferedReader br = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream()));
                        StringBuilder sb = new StringBuilder();
                        String line;
                        while ((line = br.readLine()) != null) {
                            sb.append(line + "\n");
                        }
                        Log.i(TAG,"doInBackground(), http response line:"+line);
                        jsonElemnt = new JsonParser().parse(sb.toString());
                        jsonObject = jsonElemnt.getAsJsonObject();
                        /*Further parse & instantiate FlikrPhotosResponse = */
                        br.close();
                        break;
                    //TODO: ERRORS https://www.flickr.com/services/api/flickr.groups.search.html
                    default:
                        Log.e(TAG,"doInBackground(), http response error status:"+status);
                        //TODO: handle error responses
                        break;

                }



            } catch (IOException ex) {

                ex.printStackTrace();

            } catch (Exception ex) {

                ex.printStackTrace();

            } finally {
                if (httpURLConnection != null) {
                    try {
                        httpURLConnection.disconnect();
                    } catch (Exception ex) {
                        ex.printStackTrace();
                    }
                }
            }

            return FlikrPhotosResponse;
        }//end doInBackgroud

        protected void onPostExecute(flikrPhotosResponse FlikrPhotosResponse) {

            Log.i(TAG,"onPostExecute(), FlikrPhotosResponse:"+FlikrPhotosResponse);

        }


    }//end class

Relevant logs there is no errpr or exception:

02-04 13:24:12.037 3750-4270/com.bing.ary.skywelltest I/SearchFlickerAsync: doInBackground(), http request:https://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=37ae86d629a2e4a62917253419cb9e94&tags=basketball&format=json&nojsoncallback=1&api_sig=be97f5275f5a128fbe69dc2cde2560b9
02-04 13:24:12.220 3750-4270/com.bing.ary.skywelltest I/SearchFlickerAsync: doInBackground(), http response status:200
02-04 13:24:12.221 3750-4270/com.bing.ary.skywelltest I/SearchFlickerAsync: doInBackground(), http response line:null

I also

Answer 1

You're logging the wrong thing:

while ((line = br.readLine()) != null) {
    sb.append(line + "\n");
}
Log.i(TAG,"doInBackground(), http response line:"+line);

Of course line is null at this point. That's why the loop terminated. You should be logging sb.toString() .

NB:

1. You don't need any of the following:

    httpURLConnection.setRequestMethod("GET"); httpURLConnection.setRequestProperty("Content-length", "0"); httpURLConnection.connect(); 

2. The numerous claims in comments that you need to use HttpsURLConnection are not correct. Using HttpURLConnection is perfectly valid even if the URL is an HTTPS one, as long as you don't need the extra methods of HttpsURLConnection , as HttpsURLConnection extends HttpURLConnection .