AsyncTask在第一次尝试时不会在onPostExecute上返回JSON响应，但从第二次尝试开始运行良好

Question

所以，我有一个方法，当按下按钮时会调用它，它应该向我的数据库中添加一些信息(纬度、经度等(。奇怪的行为是，当我打开应用程序时(应用程序添加了一个标记，按钮激活onMarkerClick(，如果我按下该按钮，它将不起作用，JSON的响应将是null，但使用相同的标记，第二次尝试它会很好(我在onMarkerClick中得到纬度和经度。我已经检查了我使用doInBackground发送的每个param的值，每个参数看起来都很好，都有值等。

这是一种方法：

public void RaporteazaAlerta() {
User user = SharedPrefManager.getInstance(this).getUser();
final String lat = String.valueOf(latitudine_marker);
final String longit = String.valueOf(longitudine_marker);
final String problema1 = String.valueOf(problema+1);
final String descriere1 = descriere;
final String id_user =  String.valueOf(user.getId());
id= id_user;
class  RaporteazaAlerta extends AsyncTask<Void, Void, String> {
@Override
protected String doInBackground(Void... voids) {
//creating request handler object
RequestHandler requestHandler = new RequestHandler();
//creating request parameters
HashMap<String, String> params = new HashMap<>();
params.put("latitudine", lat);
params.put("longitudine", longit);
params.put("id_problema", problema1);
params.put("ID_user", id_user);
params.put("descriere", descriere1);
//returing the response
return requestHandler.sendPostRequest(URLs.URL_ALERTA, params);
}
@Override
protected void onPreExecute() {
super.onPreExecute();
//displaying the progress bar while user registers on the server
}
@Override
protected void onPostExecute(String s) {{
super.onPostExecute(s);

try {
JSONObject obj = new JSONObject(s);
//if no error in response
if (!obj.getBoolean("error")) {
Toast.makeText(getApplicationContext(), obj.getString("message"), Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getApplicationContext(), "Nu se poate adauga alerta", Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
layout_buton.setVisibility(View.GONE);
linearLayout.setVisibility(View.GONE);
linearLayout_obs.setVisibility(View.GONE);
linearLayout_obs_inapoi.setVisibility(View.GONE);
observatii.setText(null);
hideSoftKeyboard(observatii);
}
}
}
RaporteazaAlerta report = new RaporteazaAlerta();
report.execute();
}

查看日志以获取更多信息，我发现有一个System.err:

W/System.err:java.lang.NullPointerException：尝试对null对象引用调用虚拟方法"int java.lang.String.length(("在：

2020-03-12 13:29:40.385 23142-23262/com.scopesystems.cityalert W/System.err:     at java.net.URLEncoder.encode(URLEncoder.java:205)
2020-03-12 13:29:40.385 23142-23262/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.suport.RequestHandler.getPostDataString(RequestHandler.java:69)
2020-03-12 13:29:40.385 23142-23262/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.suport.RequestHandler.sendPostRequest(RequestHandler.java:35)
2020-03-12 13:29:40.386 23142-23262/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.ui.Harta$1RaporteazaAlerta.doInBackground(Harta.java:579)
2020-03-12 13:29:40.386 23142-23262/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.ui.Harta$1RaporteazaAlerta.doInBackground(Harta.java:563)

第二次尝试时工作良好的RequestHandler，以及任何其他AsyncTask:

public class RequestHandler {
public String sendPostRequest(String requestURL, HashMap<String, String> postDataParams) {
URL url;
StringBuilder sb = new StringBuilder();
try {
url = new URL(requestURL);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(15000);
conn.setConnectTimeout(15000);
conn.setRequestMethod("POST");
conn.setDoInput(true);
conn.setDoOutput(true);
OutputStream os = conn.getOutputStream();
BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(os, "UTF-8"));
writer.write(getPostDataString(postDataParams));
writer.flush();
writer.close();
os.close();
int responseCode = conn.getResponseCode();
if (responseCode == HttpsURLConnection.HTTP_OK) {
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
sb = new StringBuilder();
String response;
while ((response = br.readLine()) != null) {
sb.append(response);
}
}
} catch (Exception e) {
e.printStackTrace();
}
return sb.toString();
}
private String getPostDataString(HashMap<String, String> params) throws UnsupportedEncodingException {
StringBuilder result = new StringBuilder();
boolean first = true;
for (Map.Entry<String, String> entry : params.entrySet()) {
if (first)
first = false;
else
result.append("&");
result.append(URLEncoder.encode(entry.getKey(), "UTF-8"));
result.append("=");
result.append(URLEncoder.encode(entry.getValue(), "UTF-8"));
}
return result.toString();
}
}

在日志中也有关于org.json.JSONException: End of input at character 0 of的内容，但我认为这是因为我没有收到来自服务器的任何响应。

EDIT：完整日志输出：

2020-03-12 13:50:13.901 23545-23598/com.scopesystems.cityalert W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
2020-03-12 13:50:13.901 23545-23598/com.scopesystems.cityalert W/System.err:     at java.net.URLEncoder.encode(URLEncoder.java:205)
2020-03-12 13:50:13.901 23545-23598/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.suport.RequestHandler.getPostDataString(RequestHandler.java:69)
2020-03-12 13:50:13.901 23545-23598/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.suport.RequestHandler.sendPostRequest(RequestHandler.java:35)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.ui.Harta$1RaporteazaAlerta.doInBackground(Harta.java:579)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.ui.Harta$1RaporteazaAlerta.doInBackground(Harta.java:563)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:304)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:243)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
2020-03-12 13:50:13.902 23545-23598/com.scopesystems.cityalert W/System.err:     at java.lang.Thread.run(Thread.java:761)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err: org.json.JSONException: End of input at character 0 of 
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at org.json.JSONTokener.syntaxError(JSONTokener.java:449)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at org.json.JSONTokener.nextValue(JSONTokener.java:97)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at org.json.JSONObject.<init>(JSONObject.java:156)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at org.json.JSONObject.<init>(JSONObject.java:173)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.ui.Harta$1RaporteazaAlerta.onPostExecute(Harta.java:594)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at com.scopesystems.cityalert.ui.Harta$1RaporteazaAlerta.onPostExecute(Harta.java:563)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at android.os.AsyncTask.finish(AsyncTask.java:660)
2020-03-12 13:50:13.906 23545-23545/com.scopesystems.cityalert W/System.err:     at android.os.AsyncTask.-wrap1(AsyncTask.java)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:677)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:102)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at android.os.Looper.loop(Looper.java:154)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:6077)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at java.lang.reflect.Method.invoke(Native Method)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
2020-03-12 13:50:13.907 23545-23545/com.scopesystems.cityalert W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)

Answer 1

根据@Mike M.的说法，我实际上错误地检查了descriere1的一个值，它实际上是null。null意味着没有添加描述，所以我更改了代码：

public void RaporteazaAlerta() {
User user = SharedPrefManager.getInstance(this).getUser();
final String lat = String.valueOf(latitudine_marker);
final String longit = String.valueOf(longitudine_marker);
final String problema1 = String.valueOf(problema+1);
String descriere1 = descriere;
if(descriere1 == null){
descriere1 = "null";
}
final String id_user =  String.valueOf(user.getId());
id= id_user;
final String finalDescriere = descriere1;
class  RaporteazaAlerta extends AsyncTask<Void, Void, String> {
@Override
protected String doInBackground(Void... voids) {
//creating request handler object
RequestHandler requestHandler = new RequestHandler();
//creating request parameters
HashMap<String, String> params = new HashMap<>();
params.put("latitudine", lat);
params.put("longitudine", longit);
params.put("id_problema", problema1);
params.put("ID_user", id_user);
params.put("descriere", finalDescriere);
//returing the response
return requestHandler.sendPostRequest(URLs.URL_ALERTA, params);
}