在Android中解析JSON时出现空指针异常

Question

在Android上解析JSON时，出现空指针异常。

这就是我想要解析JSON：

[{"value":"91.84","timestamp":"2012-10-11 14:12:13"}] 

这里是我解析的方式：

InputStream inputStream = null; 
String result = null; 
HttpResponse response; 
BufferedReader reader; 
JSONObject jObject; 
String aJsonString1; 
String aJsonString2; 


public class ReadJSON extends AsyncTask<String, Void, String> { 
    protected String doInBackground(String... url) { 

     DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams()); 
     HttpPost httppost = new HttpPost("url is written here"); 
     // Depends on your web service 
     httppost.setHeader("Content-type", "application/json"); 
     try { 
      response = httpclient.execute(httppost);  
      HttpEntity entity = response.getEntity(); 
      inputStream = entity.getContent(); 
      reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8); 
     StringBuilder sb = new StringBuilder(); 
     String line = null; 

     while ((line = reader.readLine()) != null) 
      { 
       sb.append(line + "\n"); 
      } 


     JSONArray jsonArray = new JSONArray(result); 

     for (int i=0; i < jsonArray.length(); i++) 
      { 
       JSONObject oneObject = jsonArray.getJSONObject(i); 
       // Pulling items from the array 
       String oneObjectsItem = oneObject.getString("value"); 
       String oneObjectsItem2 = oneObject.getString("timestamp"); 
      } 

     aJsonString1 = jsonArray.getJSONObject(0).getString("value"); 
     aJsonString2 = jsonArray.getJSONObject(0).getString("timestamp"); 


     return aJsonString1; 

     } catch (ClientProtocolException e) { 
      e.printStackTrace(); 
     } catch (IOException e) { 
      e.printStackTrace(); 
     } catch (IllegalStateException e) { 
      e.printStackTrace(); 
     } catch (JSONException e) { 
      e.printStackTrace(); 
      Log.e("JSON",e.getMessage() + " " + e); 
     }   
     return null; // Error case 

    } 

    protected void onPostExecute(String result) { 
     textView.setText(aJsonString1); 

     if(aJsonString1==null){ 
      textView.setText("nothing to show"); 
     } 

    } 

这是堆栈跟踪我得到：

04-26 15:37:40.930: E/AndroidRuntime(1387): FATAL EXCEPTION: AsyncTask #1 
04-26 15:37:40.930: E/AndroidRuntime(1387): java.lang.RuntimeException: An error occured while executing doInBackground() 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at android.os.AsyncTask$3.done(AsyncTask.java:299) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.util.concurrent.FutureTask.setException(FutureTask.java:219) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.util.concurrent.FutureTask.run(FutureTask.java:239) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.lang.Thread.run(Thread.java:856) 
04-26 15:37:40.930: E/AndroidRuntime(1387): Caused by: java.lang.NullPointerException 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at org.json.JSONTokener.nextValue(JSONTokener.java:94) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at org.json.JSONArray.<init>(JSONArray.java:87) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at org.json.JSONArray.<init>(JSONArray.java:103) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at com.example.ayasms.MainActivity$ReadJSON.doInBackground(MainActivity.java:176) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at com.example.ayasms.MainActivity$ReadJSON.doInBackground(MainActivity.java:1) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at android.os.AsyncTask$2.call(AsyncTask.java:287) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  at java.util.concurrent.FutureTask.run(FutureTask.java:234) 
04-26 15:37:40.930: E/AndroidRuntime(1387):  ... 4 more 

你能看到什么可能是这里的问题？

在此先感谢。

Answer 1

您传递给JSONArray构造函数的字符串对象result为null。你永远不会改变它的初始价值。