Android 使用ServiceHandler和AsyncTask从localhost获取JSON文件

我已经在www文件夹中添加了一个

questions.json

文件，我正在尝试检索它。 问题是响应总是返回null我猜异常出现在

httpClient.execute（httpGet），但不确定

@SuppressLint("NewApi")
public class QuestionListFragment extends android.app.ListFragment 
{
    private ProgressDialog pDialog;
    // url to make request
        private static String url = "http://localhost/questions.json";

        // JSON Node names
        private static final String TAG_QUESTIONS = "Questions";
        private static final String TAG_ID = "Question_Id";
        private static final String TAG_BODY = "QuestionBody";
        private static final String TAG_TITLE = "QuestionTitle";
        private static final String TAG_NAME = "Asker_Name";
        private static final String TAG_TIME = "Created At";
        private static final String TAG_ANSWERS = "Answers";
        private static final String TAG_ANSWER = "answer";
        private static final String TAG_A_NAME = "Name";
        private static final String TAG_RATING = "Rating";


        // questions JSONArray
        JSONArray questions = null;
        ListView lv;
        Context c;
        JSONObject obj ;
        ArrayList<HashMap<String, String>> questionsList = new ArrayList<HashMap<String, String>>();

    @Override
    public View onCreateView( LayoutInflater inflater, 
        ViewGroup container,
        Bundle savedInstanceState )
    {

        View view = inflater.inflate(ask.code.R.layout.questions_list_frag, container, false);


         new GetQuestions().execute();

         return view;
    }

    private class GetQuestions extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Showing progress dialog
            pDialog = new ProgressDialog(getActivity());
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();

        }
        @Override
        protected Void doInBackground(Void... arg0) {
            // Creating service handler class instance
            ServiceHandler sh = new ServiceHandler();
            String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);
            Log.d("Response: ", "> " + jsonStr);

            if (jsonStr != null) {
                try{
                    JSONObject jsonObj = new JSONObject(jsonStr);

                    // Getting JSON Array node
                    questions = jsonObj.getJSONArray(TAG_QUESTIONS);



                        // looping through All Questions
                        for(int i = 0; i < questions.length(); i++){
                            JSONObject c = questions.getJSONObject(i);


                            String id = c.getString(TAG_ID);
                            String title = c.getString(TAG_TITLE);
                            String body = c.getString(TAG_BODY);
                            String name = c.getString(TAG_NAME);
                            String time = c.getString(TAG_TIME);


                            JSONObject answers = c.getJSONObject(TAG_ANSWERS);
                            String answer = answers.getString(TAG_ANSWER);
                            String a_name = answers.getString(TAG_A_NAME);
                            String a_rating = answers.getString(TAG_RATING);

                            // creating new HashMap
                            HashMap<String, String> map = new HashMap<String, String>();

                            // adding each child node to HashMap key => value
                            map.put(TAG_ID, id);
                            map.put(TAG_NAME, name);
                            map.put(TAG_TITLE, title);
                            map.put(TAG_BODY, body);

                            // adding HashList to ArrayList
                            questionsList.add(map);
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                } else {
                Log.e("ServiceHandler", "Couldn't get any data from the url");
            }

            return null;
        }
        @Override
        protected void onPostExecute(Void result) {
            super.onPostExecute(result);
            // Dismiss the progress dialog
            if (pDialog.isShowing())
                pDialog.dismiss();
            /**
             * Updating parsed JSON data into ListView
             * */
            ListAdapter adapter = new SimpleAdapter(
                    getActivity(), 
                    questionsList, 
                    ask.code.R.layout.question_item,
                    new String[] {
                        TAG_NAME,
                        TAG_TITLE,
                        TAG_TIME},
                    new int[] {
                        ask.code.R.id.asker_name,
                        ask.code.R.id.question_title,
                        ask.code.R.id.question_rating});


            setListAdapter(adapter);



                }



    }


    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        // TODO Auto-generated method stub

        super.onListItemClick(l, v, position, id);  

    }






        // TODO Auto-generated method stub







}

如果您使用的是emulator，那么您必须编写10.0.2.2来代替localhost。
如果您正在使用您的设备，那么您必须连接到同一网络，并且必须用您的计算机ip地址替换localhost

我希望这将有助于
您尝试通过指定
localhost
作为承载服务的系统的地址来连接到服务器。Android仿真器在虚拟机（QEMU）中运行。因此，
localhost
将是仿真器自己的环回地址，而不是系统的环回地址。

因此，您可以在Windows中转到CommandPrompt获取系统的IP地址，也可以使用
http://10.0.2.2:8080/...
而不是使用
localhost

私有静态字符串url=”http://10.0.2.2:8080/questions.json";
公共字符串makeServiceCall（字符串url，int方法，
public String makeServiceCall(String url, int method,
                              List<NameValuePair> params) {

    StringBuilder result = new StringBuilder();

    try {
        //URL urlObj = new URL(url);
        URL urlObj = new URL(url.replace(" ","%20"));
        urlConnection = (HttpURLConnection) urlObj.openConnection();
        InputStream in = new BufferedInputStream(urlConnection.getInputStream());

        BufferedReader reader = new BufferedReader(new InputStreamReader(in));

        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }

    }catch( Exception e) {
        e.printStackTrace();
    }
    finally {
        urlConnection.disconnect();
    }


    return result.toString();
}

列表参数）{
StringBuilder结果=新建StringBuilder（）；
试一试{
//URL urlObj=新URL（URL）；
URL urlObj=新URL（URL.replace（“，“%20”）；
urlConnection=（HttpURLConnection）urlObj.openConnection（）；
InputStream in=new BufferedInputStream（urlConnection.getInputStream（））；
BufferedReader reader=新的BufferedReader（新的InputStreamReader（in））；
弦线；
而（（line=reader.readLine（））！=null）{
结果。追加（行）；
}
}捕获（例外e）{
e、 printStackTrace（）；
}
最后{
urlConnection.disconnect（）；
}
返回result.toString（）；
}
这可能会有帮助：

public class ServiceHandler {

static String response = null;
public final static int GET = 1;
public final static int POST = 2;
HttpURLConnection urlConnection;
public ServiceHandler() {

}
public String makeServiceCall(String url, int method) {
    return this.makeServiceCall(url, method, null);
}
public String makeServiceCall(String url, int method,
                              List<NameValuePair> params) {
    StringBuilder result = new StringBuilder();


    try {
        //URL urlObj = new URL(url);
        URL urlObj = new URL(url.replace(" ","%20"));
        urlConnection = (HttpURLConnection) urlObj.openConnection();
        InputStream in = new       BufferedInputStream(urlConnection.getInputStream());

        BufferedReader reader = new BufferedReader(new    InputStreamReader(in));

        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }

    }catch( Exception e) {
        e.printStackTrace();
    }
    finally {
        urlConnection.disconnect();
    }


    return result.toString();
   }
   }

公共类ServiceHandler{
静态字符串响应=null；
公共最终静态int GET=1；
公共最终静态int POST=2；
HttpURLConnection-urlConnection；
公共服务处理程序（）{
}
公共字符串makeServiceCall（字符串url，int方法）{
返回此.makeServiceCall（url，方法，null）；
}
公共字符串makeServiceCall（字符串url，int方法，
列表参数）{
StringBuilder结果=新建StringBuilder（）；
试一试{
//URL urlObj=新URL（URL）；
URL urlObj=新URL（URL.replace（“，“%20”）；
urlConnection=（HttpURLConnection）urlObj.openConnection（）；
InputStream in=new BufferedInputStream（urlConnection.getInputStream（））；
BufferedReader reader=新的BufferedReader（新的InputStreamReader（in））；
弦线；
而（（line=reader.readLine（））！=null）{
结果。追加（行）；
}
}捕获（例外e）{
e、 printStackTrace（）；
}
最后{
urlConnection.disconnect（）；
}
返回result.toString（）；
}
}
下面这看起来像是soumit未解释代码转储的副本。请张贴事实上是问题答案的原始答案。
public String makeServiceCall(String url, int method,
                              List<NameValuePair> params) {

    StringBuilder result = new StringBuilder();

    try {
        //URL urlObj = new URL(url);
        URL urlObj = new URL(url.replace(" ","%20"));
        urlConnection = (HttpURLConnection) urlObj.openConnection();
        InputStream in = new BufferedInputStream(urlConnection.getInputStream());

        BufferedReader reader = new BufferedReader(new InputStreamReader(in));

        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }

    }catch( Exception e) {
        e.printStackTrace();
    }
    finally {
        urlConnection.disconnect();
    }


    return result.toString();
}

public class ServiceHandler {

static String response = null;
public final static int GET = 1;
public final static int POST = 2;
HttpURLConnection urlConnection;
public ServiceHandler() {

}
public String makeServiceCall(String url, int method) {
    return this.makeServiceCall(url, method, null);
}
public String makeServiceCall(String url, int method,
                              List<NameValuePair> params) {
    StringBuilder result = new StringBuilder();


    try {
        //URL urlObj = new URL(url);
        URL urlObj = new URL(url.replace(" ","%20"));
        urlConnection = (HttpURLConnection) urlObj.openConnection();
        InputStream in = new       BufferedInputStream(urlConnection.getInputStream());

        BufferedReader reader = new BufferedReader(new    InputStreamReader(in));

        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }

    }catch( Exception e) {
        e.printStackTrace();
    }
    finally {
        urlConnection.disconnect();
    }


    return result.toString();
   }
   }