FileOutputStream問題與寫入JSON從URL到內部存儲

我正在寫一個JSON文件被訪問，以消除從我的應用程序的網絡訪問/延遲儘可能多。我還沒有處理過將文件寫入內存的問題，並從Google的文檔中讀取了大部分讀/寫代碼，但我仍然遇到問題。FileOutputStream問題與寫入JSON從URL到內部存儲

目前，我在這條線得到一個空指針異常：

FileOutputStream fOut = openFileOutput("runesInfo.json", Context.MODE_PRIVATE)

這使我相信，從來沒有創建的文件，或者說我初始化它錯了，但我不知道怎麼樣。

完整的代碼段：

public class GetRunes extends AsyncTask<String, String, String> { 

     boolean runesCached = false; 

     protected String doInBackground(String[] runeId) { 
      String url = "https://prod.api.pvp.net/api/lol/static-data/" + region + "/v1.2/rune?api_key=" + api_key; 
      JSONParser jsonParser = new JSONParser(); 
      JSONObject runeInfo = jsonParser.getJSONFromUrl(url); 
      String jsonString = runeInfo.toString(); 
      String readJson = null; 
      Context context = GetStaticData.this; 

      if(!runesCached) { 
       Log.d("Cache", "Caching File"); 

       try { 
        File file = new File(context.getFilesDir(), "runesInfo.json"); 
        FileOutputStream fOut = openFileOutput("runesInfo.json", Context.MODE_PRIVATE); 
        fOut.write(jsonString.getBytes()); 
        fOut.close(); 
        Log.d("Cache", "Cache Complete"); 
        runesCached = true; 

       } catch (Exception e){ 
        e.printStackTrace(); 
       } 

      } 

      String name = null; 
      try { 
       FileInputStream fis = openFileInput("runesInfo.json"); 
       InputStreamReader isr = new InputStreamReader(fis); 

       fis.read(readJson.getBytes()); 
       JSONObject storedJson = new JSONObject(readJson); 
       Log.d("Stored JSON", "" + storedJson); 
       JSONObject idJson = storedJson.getJSONObject("data"); 
       JSONObject single = idJson.getJSONObject(runeId[0]); 


       try { 
        name = single.getString("name"); 
       } catch (JSONException e) { 
        e.printStackTrace(); 
       } 

      } catch (FileNotFoundException e) { 
       e.printStackTrace(); 
      } catch (StreamCorruptedException e) { 
       e.printStackTrace(); 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } catch (JSONException e) { 
       e.printStackTrace(); 
      } 
      return name; 
     } 
    }

的logcat：

04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats D/Cache﹕ Caching File 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ java.lang.NullPointerException 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at android.content.ContextWrapper.getFilesDir(ContextWrapper.java) 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.GetStaticData$GetRunes.doInBackground(GetSt 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.GetStaticData$GetRunes.doInBackground(GetSt 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java) 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java) 
04-29 09:53:58.199 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java) 
04-29 09:53:58.209 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor. 
04-29 09:53:58.209 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor 
04-29 09:53:58.209 11273-11732/edu.appdesign.leaguestats W/System.err﹕ at java.lang.Thread.run(Thread.java) 
04-29 09:53:58.209 11273-11273/edu.appdesign.leaguestats W/System.err﹕ java.util.concurrent.ExecutionException: java.lang.NullPointerException 
04-29 09:53:58.209 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.FutureTask.report(FutureTask.java) 
04-29 09:53:58.209 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.FutureTask.get(FutureTask.java) 
04-29 09:53:58.209 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask.get(AsyncTask.java) 
04-29 09:53:58.209 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.GetStaticData.getRuneInfo(GetStaticData.jav 
04-29 09:53:58.209 11273-11732/edu.appdesign.leaguestats W/dalvikvm﹕ threadid=20: thread exiting with uncaught exception (group=0x41650e18) 
04-29 09:53:58.209 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.RunesActivity$GetRunes.onPostExecute(RunesA 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.RunesActivity$GetRunes.onPostExecute(RunesA 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask.finish(AsyncTask.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask.access$600(AsyncTask.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.Looper.loop(Looper.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method) 

04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java) 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit 
04-29 09:53:58.219 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:133) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at dalvik.system.NativeStart.main(Native Method) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ Caused by: java.lang.NullPointerException 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.content.ContextWrapper.openFileInput(ContextWrapper.java) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.GetStaticData$GetRunes.doInBackground(GetSt 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at edu.appdesign.leaguestats.GetStaticData$GetRunes.doInBackground(GetSt 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask$2.call(AsyncTask.java) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java) 
04-29 09:53:58.229 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor. 
04-29 09:53:58.239 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor 
04-29 09:53:58.239 11273-11273/edu.appdesign.leaguestats W/System.err﹕ at java.lang.Thread.run(Thread.java)

來源

2014-04-29 Nate

請分享logcat。 –

@ManishMulimani相關logcat部分加入 – Nate

我想，這可能是因爲錯誤的上下文。 GetRunes內部類是什麼？ openFileOutput是Context的一種方法（很可能是Activity）。在代碼中它可能爲空，因爲doInBackground在單獨的線程中執行。所以，嘗試添加「上下文」。並檢查它是否不爲空。順便說一句，儘量避免在靜態變量中保持上下文。 – Olsavage

我建議使用Android Service。我認爲，它會適合您的需要。只需將代碼移動到Service，擺脫靜態上下文，在onStartCommand方法中執行AsyncTask，並在需要保存JSON時調用startService。

來源

2014-04-30 11:47:24 Olsavage

File file = new File(context.getFilesDir(), "runesInfo.json"); 
FileOutputStream fOut = openFileOutput("runesInfo.json", Context.MODE_PRIVATE);

您創建了一個文件實例，但從未在流中使用它。

FileOutputStream fOut = new FileOutputStream(new File(context.getFilesDir(), "runesInfo.json"));

應該做的工作。

來源

2014-09-07 22:06:54

FileOutputStream問題與寫入JSON從URL到內部存儲

回答

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