Java NetworkOnMainThreadException從URL讀取csv文件

Question

你好我正在使用android studio創建一個應用程序，我遇到了一個錯誤，這證明自己很難解決。我想要做的就是從網址中讀取一個CSV文件，併爲每一行添加值到地圖標記。我可以很容易地從文件中讀取並添加到我的標誌，但這個網址CSV讀取被證明是一個挑戰，對我來說:(。什麼是我的錯，請甚至更好的可以不必過於簡化。

HttpURLConnection conn = null; 
    try { 
     URL url = new URL("http://www.free-map.org.uk/course/mad/ws/get.php?username=user002&format=csv"); 
     conn = (HttpURLConnection) url.openConnection(); 
     InputStream in = conn.getInputStream(); 
     if(conn.getResponseCode() == 200) 
     { 
      BufferedReader br = new BufferedReader(new InputStreamReader(in)); 
      String inputLine; 
      while ((inputLine = br.readLine()) != null) { 
       String[] comps = inputLine.split(","); 
       if (comps.length == 5) { 
        OverlayItem currentItem = new OverlayItem(comps[0], comps[2], new GeoPoint(Double.parseDouble(comps[4]), Double.parseDouble(comps[3]))); 
        pois.addItem(currentItem); 
       } 
      } 
     } 

    }catch (IOException e){ 
     new AlertDialog.Builder(this).setMessage("ERROR: "+e).show(); 
    } 
    finally 
    { 
     if(conn!=null) 
      conn.disconnect(); 
    } 

我有（）這段代碼放在我的簡歷，以測試它是否工作是否有幫助。而這些都是在logcat中顯示的錯誤。

E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: com.example.edwin.mapping, PID: 2048 
        java.lang.RuntimeException: Unable to resume activity {com.example.edwin.mapping/com.example.edwin.mapping.HelloMap}: android.os.NetworkOnMainThreadException 
         at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2788) 
         at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2817) 
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250) 
         at android.app.ActivityThread.access$800(ActivityThread.java:135) 
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
         at android.os.Handler.dispatchMessage(Handler.java:102) 
         at android.os.Looper.loop(Looper.java:136) 
         at android.app.ActivityThread.main(ActivityThread.java:5017) 
         at java.lang.reflect.Method.invokeNative(Native Method) 
         at java.lang.reflect.Method.invoke(Method.java:515) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
         at dalvik.system.NativeStart.main(Native Method) 
        Caused by: android.os.NetworkOnMainThreadException 
         at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145) 
         at java.net.InetAddress.lookupHostByName(InetAddress.java:385) 
         at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236) 
         at java.net.InetAddress.getAllByName(InetAddress.java:214) 
         at com.android.okhttp.internal.Dns$1.getAllByName(Dns.java:28) 
         at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:216) 
         at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:122) 
         at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:292) 
         at com.android.okhttp.internal.http.HttpEngine.sendSocketRequest(HttpEngine.java:255) 
         at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:206) 
         at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:345) 
         at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:296) 
         at com.android.okhttp.internal.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:179) 
         at com.example.edwin.mapping.HelloMap.onResume(HelloMap.java:158) 
         at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192) 
         at android.app.Activity.performResume(Activity.java:5310) 
         at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2778) 
         at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2817)  
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2250)  
         at android.app.ActivityThread.access$800(ActivityThread.java:135)  
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)  
         at android.os.Handler.dispatchMessage(Handler.java:102)  
         at android.os.Looper.loop(Looper.java:136)  
         at android.app.ActivityThread.main(ActivityThread.java:5017)  
         at java.lang.reflect.Method.invokeNative(Native Method)  
         at java.lang.reflect.Method.invoke(Method.java:515)  
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)  
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)  
         at dalvik.system.NativeStart.main(Native Method)  
Application terminated. 

Answer 1

使用Async Task進行網絡操作。不要運行它在UI線程上。

例如：

private class ReadFile extends AsyncTask<String, Void, String> { 

    @Override 
    protected String doInBackground(String... params) { 
     HttpURLConnection conn = null; 
     try { 
      URL url = new URL("http://www.free-map.org.uk/course/mad/ws/get.php?username=user002&format=csv"); 
      conn = (HttpURLConnection) url.openConnection(); 
      InputStream in = conn.getInputStream(); 
      if(conn.getResponseCode() == 200) 
      { 
       BufferedReader br = new BufferedReader(new InputStreamReader(in)); 
       String inputLine; 
       while ((inputLine = br.readLine()) != null) { 
        String[] comps = inputLine.split(","); 
        if (comps.length == 5) { 
         OverlayItem currentItem = new OverlayItem(comps[0], comps[2], new GeoPoint(Double.parseDouble(comps[4]), Double.parseDouble(comps[3]))); 
         pois.addItem(currentItem); 
        } 
       } 
      } 

     }catch (Exception e){ 
      Log.e("Error, e.toString()); 
     } 
     finally 
     { 
      if(conn!=null) 
       conn.disconnect(); 
     } 
     return null; 
    } 

    @Override 
    protected void onPostExecute(String result) { 

    } 

    @Override 
    protected void onPreExecute() {} 
} 

現在把它用：

new ReadFile().execute("");