我在Android上解析JSON时遇到Null指针异常。
这是我要解析的JSON:
[{"value":"91.84","timestamp":"2012-10-11 14:12:13"}]
以下是我解析它的方式:
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");
}
}
这是我得到的堆栈跟踪:
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
你能看到这里可能出现的问题吗?
提前致谢。
答案 0 :(得分:3)
您传递到result
构造函数的String对象JSONArray
是null
。你永远不会从初始值改变它。