所以我在使此代码正常工作时遇到了一些问题,我在网上找到了部分代码,但无法正常工作。我曾尝试调整一些代码,但是无论我在做什么,该应用程序都会因错误而崩溃。经过数小时的谷歌搜索和观看YouTube教程,我一直在尝试使它工作几天,但似乎无法使它正常工作。
有人可以告诉我我在这里做错了什么吗?
CODE:
public class fetchJSON extends AsyncTask<Void, Void, String> {
@Override
protected String doInBackground(Void... params) {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
URL url;
try {
url = new URL("www.link.to.json");
urlConnection.setRequestMethod("GET"); //Your method here
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null)
buffer.append(line + "\n");
if (buffer.length() == 0)
return null;
return buffer.toString();
} catch (IOException e) {
Log.e(TAG, "IO Exception", e);
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(TAG, "Error closing stream", e);
}
}
}
}
@Override
protected void onPostExecute(String response) {
if(response != null) {
JSONObject json = null;
try {
json = new JSONObject(response);
} catch (JSONException e) {
e.printStackTrace();
}
JSONObject jsonResponse = null;
try {
jsonResponse = json.getJSONObject("Question1");
} catch (JSONException e) {
e.printStackTrace();
}
MainActivity.jsonPrint.setText((CharSequence) jsonResponse);
}
}
}
错误:
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
Process: uk.co.jrtevents.fetchjsonfromurltest, PID: 4019
java.lang.RuntimeException: An error occurred while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:318)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)
Caused by: java.lang.NullPointerException: Attempt to invoke a virtual method on a null object reference
at uk.co.jrtevents.fetchjsonfromurltest.fetchJSON.doInBackground(fetchJSON.java:31)
at uk.co.jrtevents.fetchjsonfromurltest.fetchJSON.doInBackground(fetchJSON.java:18)
at android.os.AsyncTask$2.call(AsyncTask.java:304)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
LINE 31:urlConnection.setRequestMethod("GET");
HttpURLConnection urlConnection = null;
您从未为urlConnection
分配值,因此它是null
。
您需要添加:
urlConnection = url.openConnection();
尝试使用urlConnection
之前。
URL
和HttpURLConnection
已经很老了,几乎没有开发人员使用它们了。使用更现代的HTTP客户端API(例如OkHttp)可能会更好。