Java.net.UnknownHostExceptionを解決する方法
マニフェストファイルでインターネットの許可を得た。モバイルネットワーク接続も機能しています。メインコード：
/**
* Created by Yogesh on 5/07/2016.
*/
public class All_Item_Fragment extends Android.support.v4.app.ListFragment {
// Declare Variables
JSONArray jsonarray = null;
ListView list;
ListViewAdapter adapter;
ArrayList<HashMap<String, String>> itemlist;
static String NAME = "name";
static String DESCRIPTION = "Description";
static String PRICE = "price";
static String IMAGE = "image_path";
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.all_item_layout, container, false);
itemlist = new ArrayList<HashMap<String, String>>();
new ReadJSON().execute();
list = (ListView) view.findViewById(Android.R.id.list);
return view;
}
private class ReadJSON extends AsyncTask<Void, Void, Void> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected Void doInBackground(Void... params) {
// Create an array
itemlist = new ArrayList<HashMap<String, String>>();
// Retrieve JSON Objects from the given URL address
JSONObject jsonobject = JSONfunctions.getJSONfromURL("http://mahatiffin.com/web/selectallmenu.php");
try {
// Locate the array name in JSON
jsonarray = jsonobject.getJSONArray("AllMenu");
for (int i = 0; i < jsonarray.length(); i++) {
HashMap<String, String> map = new HashMap<String, String>();
jsonobject = jsonarray.getJSONObject(i);
// Retrive JSON Objects
map.put("name", jsonobject.getString("name"));
map.put("Description", jsonobject.getString("Description"));
map.put("price", jsonobject.getString("price"));
map.put("image_path", jsonobject.getString("image_path"));
// Set the JSON Objects into the array
itemlist.add(map);
}
} catch (JSONException e) {
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(Void args) {
// Pass the results into ListViewAdapter.Java
adapter = new ListViewAdapter(getActivity(), itemlist);
// Set the adapter to the ListView
list.setAdapter((ListAdapter) adapter);
}
}
}
public class JSONfunctions {
public static JSONObject getJSONfromURL(String url) {
InputStream is = null;
String result = "";
JSONObject jArray = null;
// Download JSON data from URL
try {
HttpClient httpclient = new DefaultHttpClient();
HttpPost httppost = new HttpPost(url);
HttpResponse response = httpclient.execute(httppost);
HttpEntity entity = response.getEntity();
is = entity.getContent();
} catch (Exception e) {
Log.e("log_tag", "Error in http connection " + e.toString());
}
// Convert response to string
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();
result = sb.toString();
} catch (Exception e) {
Log.e("log_tag", "Error converting result " + e.toString());
}
try {
jArray = new JSONObject(result);
} catch (JSONException e) {
Log.e("log_tag", "Error parsing data " + e.toString());
}
return jArray;
}
}
5月のフラグメントページでは何も表示されず、空白のページのみが表示されます。
ログ出力：
>05-18 17:43:11.730 27019-27019/com.androidbelieve.MahaTiffin D/dalvikvm: VFY: replacing opcode 0x6f at 0x0000
05-18 17:43:11.740 27019-27082/com.androidbelieve.MahaTiffin E/log_tag: Error converting result Java.lang.NullPointerException
05-18 17:43:11.740 27019-27082/com.androidbelieve.MahaTiffin E/log_tag: Error parsing data org.json.JSONException: End of input at character 0 of
05-18 17:43:11.770 27019-27082/com.androidbelieve.MahaTiffin W/dalvikvm: threadid=12: thread exiting with uncaught exception (group=0x40e11378)
05-18 17:43:11.770 27019-27082/com.androidbelieve.MahaTiffin E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Java.lang.RuntimeException: An error occured while executing doInBackground()
at Android.os.AsyncTask$3.done(AsyncTask.Java:299)
at Java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.Java:273)
at Java.util.concurrent.FutureTask.setException(FutureTask.Java:124)
at Java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.Java:307)
at Java.util.concurrent.FutureTas...(FutureTask.Java:137)
at Android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.Java:230)
at Java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.Java:1076)
at Java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.Java:569)
at Java.lang.Thread.run(Thread.Java:856)
Caused by: Java.lang.NullPointerException
at com.androidbelieve.MahaTiffin.All_Item_Fragment$ReadJSON.doInBackground(All_Item_Fragment.Java:58)
at com.androidbelieve.MahaTiffin.All_Item_Fragment$ReadJSON.doInBackground(All_Item_Fragment.Java:43)
at Android.os.AsyncTask$2.call(AsyncTask.Java:287)
at Java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.Java:305)
at Java.util.concurrent.FutureTas...(FutureTask.Java:137)
at Android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.Java:230)
at Java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.Java:1076)
at Java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.Java:569)
at Java.lang.Thread.run(Thread.Java:856)
05-18 17:43:12.420 27019-27019/com.androidbelieve.MahaTiffin W/FragmentManager: moveToState: Fragment state for Veg_Item_Fragment{415d7030 #1 id=0x7f0c00a0 Android:switcher:2131493024:1} not updated inline; expected state 3 found 2
05-18 17:43:12.530 27019-27104/com.androidbelieve.MahaTiffin E/log_tag: Error in http connection Java.net.UnknownHostException: Unable to resolve Host "mahatiffin.com": No address associated with hostname
05-18 17:43:12.540 27019-27104/com.androidbelieve.MahaTiffin E/log_tag: Error converting result Java.lang.NullPointerException
05-18 17:43:12.540 27019-27104/com.androidbelieve.MahaTiffin E/log_tag: Error parsing data org.json.JSONException: End of input at character 0 of
05-18 17:43:12.570 27019-27104/com.androidbelieve.MahaTiffin W/dalvikvm: threadid=14: thread exiting with uncaught exception (group=0x40e11378)
05-18 17:43:12.570 27019-27104/com.androidbelieve.MahaTiffin I/Process: Sending signal. PID: 27019 SIG: 9
どうすれば修正できますか？
理由：通常、UnknownHostExceptionは、指定したURLのDNSレコードを解決できない場合に発生します。その操作には妥当なタイムアウトがありますが、Wi-Fi接続が弱いか、デバイスに十分な信号がない場合、要求の送信と応答の受信の中間で通信が中断される可能性があるため、デバイスは応答を受信しないため、DNSタイムアウトであると見なされます。
要するに、例外には主に2つの理由があります。
- Wi-Fi信号が弱い場合。
- デバイスがWi-Fiに接続しているがインターネットが利用できない場合。
ソリューション：リクエストする前に、インターネットの可用性を確認してください
public static boolean isInternetOn(Context context) {
if (isMobileOrWifiConnectivityAvailable(context)) {
try {
HttpURLConnection urlc = (HttpURLConnection) (new URL("http://www.google.com").openConnection());
urlc.setRequestProperty("User-Agent", "Test");
urlc.setRequestProperty("Connection", "close");
urlc.setConnectTimeout(1500);
urlc.connect();
return (urlc.getResponseCode() == 200);
} catch (Exception e) {
DebugLog.console("Couldn't check internet connection Exception is : " + e);
}
} else {
DebugLog.console("Internet not available!");
}
return false;
}
public static boolean isMobileOrWifiConnectivityAvailable(Context ctx) {
boolean haveConnectedWifi = false;
boolean haveConnectedMobile = false;
try {
ConnectivityManager cm = (ConnectivityManager) ctx.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo[] netInfo = cm.getAllNetworkInfo();
for (NetworkInfo ni : netInfo) {
if (ni.getTypeName().equalsIgnoreCase("WIFI"))
if (ni.isConnected()) {
haveConnectedWifi = true;
}
if (ni.getTypeName().equalsIgnoreCase("MOBILE"))
if (ni.isConnected()) {
haveConnectedMobile = true;
}
}
} catch (Exception e) {
DebugLog.console("[ConnectionVerifier] inside isInternetOn() Exception is : " + e.toString());
}
return haveConnectedWifi || haveConnectedMobile;
}
_ connection successful
{
"AllMenu": [{
"0": "3",
"menu_id": "3",
"1": "Aloo Parathas",
"name": "Aloo Parathas",
"2": "170",
"price": "170",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/1.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/1.jpg",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "1",
"type_id": "1"
}, {
"0": "7",
"menu_id": "7",
"1": "ZzaxZxszsc",
"name": "ZzaxZxszsc",
"2": "343",
"price": "343",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/2.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/2.jpg",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "1",
"type_id": "1"
}, {
"0": "8",
"menu_id": "8",
"1": "sdcsdvsd",
"name": "sdcsdvsd",
"2": "435",
"price": "435",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/3.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/3.jpg",
"5": "Special-menu",
"menu_cat": "Special-menu",
"6": "2",
"type_id": "2"
}, {
"0": "9",
"menu_id": "9",
"1": "sadcasc",
"name": "sadcasc",
"2": "435",
"price": "435",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/4.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/4.jpg",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "2",
"type_id": "2"
}, {
"0": "10",
"menu_id": "10",
"1": "sadcasc",
"name": "sadcasc",
"2": "456",
"price": "456",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/5.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/5.jpg",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "1",
"type_id": "1"
}, {
"0": "11",
"menu_id": "11",
"1": "sda",
"name": "sda",
"2": "234",
"price": "234",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/6.JPG",
"image_path": "http:\/\/mahatiffin.com\/uploads\/6.JPG",
"5": "Special-menu",
"menu_cat": "Special-menu",
"6": "2",
"type_id": "2"
}, {
"0": "12",
"menu_id": "12",
"1": "sadcasc",
"name": "sadcasc",
"2": "324",
"price": "324",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/7.JPEG",
"image_path": "http:\/\/mahatiffin.com\/uploads\/7.JPEG",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "1",
"type_id": "1"
}, {
"0": "14",
"menu_id": "14",
"1": "sadcasc",
"name": "sadcasc",
"2": "232",
"price": "232",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/1.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/1.jpg",
"5": "Special-menu",
"menu_cat": "Special-menu",
"6": "1",
"type_id": "1"
}, {
"0": "15",
"menu_id": "15",
"1": "sadcasc",
"name": "sadcasc",
"2": "325",
"price": "325",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/2.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/2.jpg",
"5": "Special-menu",
"menu_cat": "Special-menu",
"6": "2",
"type_id": "2"
}, {
"0": "16",
"menu_id": "16",
"1": "sadcasc",
"name": "sadcasc",
"2": "344",
"price": "344",
"3": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"Description": "fjhsjfh jfhrwkjfh wejfhwkh ewjfhwjeh ewjfhkwe ewbfjeh wejhfkjwhhef ehfkwh wewjrh",
"4": "http:\/\/mahatiffin.com\/uploads\/4.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/4.jpg",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "1",
"type_id": "1"
}, {
"0": "18",
"menu_id": "18",
"1": "edfwdfewr",
"name": "edfwdfewr",
"2": "23",
"price": "23",
"3": "xasx scasc dqedqd edbhwd dwh3ej1 1wh1e2ue 3eh3ue e2euh23ueej ewnwencj",
"Description": "xasx scasc dqedqd edbhwd dwh3ej1 1wh1e2ue 3eh3ue e2euh23ueej ewnwencj",
"4": "http:\/\/mahatiffin.com\/uploads\/4.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/4.jpg",
"5": "Regular-menu",
"menu_cat": "Regular-menu",
"6": "2",
"type_id": "2"
}, {
"0": "19",
"menu_id": "19",
"1": "Aloo Gobi",
"name": "Aloo Gobi",
"2": "250",
"price": "250",
"3": "Aloo Sabzi, 2 Puris, Rice, Dal, Shrikhand",
"Description": "Aloo Sabzi, 2 Puris, Rice, Dal, Shrikhand",
"4": "http:\/\/mahatiffin.com\/uploads\/1.jpg",
"image_path": "http:\/\/mahatiffin.com\/uploads\/1.jpg",
"5": "Special-menu",
"menu_cat": "Special-menu",
"6": "1",
"type_id": "1"
}]
}
_文字列「接続成功」をページの開始時にPhp Jsonから削除します。
2）問題クラスキャスト例外：以下のように変更：
_@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.all_item_layout, container, false);
itemlist = new ArrayList<HashMap<String, String>>();
new ReadJSON().execute();
list = (ListView) view.findViewById(Android.R.id.list);
// Pass the results into ListViewAdapter.Java
adapter = new ListViewAdapter(getActivity(), itemlist);
// Set the adapter to the ListView
list.setAdapter((ListAdapter) adapter);
return view;
}
_そして
_@Override
protected void onPostExecute(Void args) {
adapter.notifydatasetchanged();
}
_そして
doInBackground()メソッドから「itemlist = new ArrayList>（）;」を削除します。