我在Android Studio中，我正在尝试创建一个可以进行网络连接的Android应用。我可以获得一些JSON数据，但每当我将我得到的字符串转换为JSONObject时，都会抛出NullPointerException。这是我的日志错误：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
at org.json.JSONTokener.nextValue(JSONTokener.java:94)
at org.json.JSONObject.<init>(JSONObject.java:156)
at org.json.JSONObject.<init>(JSONObject.java:173)
at com.daita.getdusa.GetDataTask.doInBackground(GetDataTask.java:58)
at com.daita.getdusa.GetDataTask.doInBackground(GetDataTask.java:21)
at android.os.AsyncTask$2.call(AsyncTask.java:295)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
at java.lang.Thread.run(Thread.java:818)
导致异常的代码行是：
JSONObject object = new JSONObject(result);
修改
我被要求添加更多源代码，所以这里是（The AsyncTask）
public class GetDataTask extends AsyncTask<Void, Void, String> {
TextView submitView;
public GetDataTask(TextView submitView){
this.submitView = submitView;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
submitView.setText("Loading...");
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
submitView.setText(s);
}
@Override
protected String doInBackground(Void... voids) {
String result;
result = getJSON("http://api.datausa.io/attrs/geo/");
JSONArray data;
List<String> parsedData = null;
List<String> geoID = new ArrayList<>();
try {
JSONObject jsonObject = new JSONObject(result);
data = jsonObject.getJSONArray("data");
parsedData = new ArrayList<>();
Log.i("DUSA", String.valueOf(jsonObject.length()));
for(int i=0; i < data.length(); i++){
parsedData.add(data.getString(i));
}
for(String string: parsedData){
//8, 9
String[] dta = string.split(",");
String populationResult = getJSON("http://api.datausa.io/api/?show=geo&sumlevel=all&required=pop&year=latest&geo="+dta[9].substring(1, dta[9].length()-1));
if (result != null && result != "{\"error\": \"No tables can match the specified query.\"}") {
JSONObject popObject = new JSONObject(populationResult);
JSONArray popData = popObject.getJSONArray("data");
String section = popData.getString(0);
geoID.add(dta[8] + "," + dta[9] + "," + section);
} else{
geoID.add(dta[8] + "," + dta[9] + ", null");
}
}
} catch (JSONException e) {
e.printStackTrace();
}
return geoID.toString();
}
public String getJSON(String url) {
HttpURLConnection c = null;
try {
URL u = new URL(url);
c = (HttpURLConnection) u.openConnection();
c.connect();
int status = c.getResponseCode();
switch (status) {
case 200:
case 201:
BufferedReader br = new BufferedReader(new InputStreamReader(c.getInputStream()));
StringBuilder sb = new StringBuilder();
String line;
while ((line = br.readLine()) != null) {
sb.append(line+"\n");
}
br.close();
return sb.toString();
}
} catch (Exception ex) {
return ex.toString();
} finally {
if (c != null) {
try {
c.disconnect();
} catch (Exception ex) {
}
}
}
return null;
}
}
注意：如果您想要实时更新源代码，请查看这些文件https://www.dropbox.com/sh/5852rt2rakk6iii/AAAgjsqOTsFfP1N4kS1KzuTBa?dl=0
答案 0 :(得分：0)
尝试为你做这一切，但让我一步一步让你更简单：
package com.daita.getdusa;
import android.content.Context;
import android.os.AsyncTask;
import android.widget.TextView;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
/**
* Created by User on 8/12/2016.
*/
public class GetDataTask extends AsyncTask<String, Void, Void>{
// Put in Main never here.
String result;
String allValues;
Context context;
public GetDataTask(Context mContext){
this.context = mContext;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
((TextView)((MainActivity)context).findViewById(R.id.resultView)).setText("Loading...");
}
@Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
((TextView)((MainActivity)context).findViewById(R.id.resultView)).setText(result);
}
@Override
protected Void doInBackground(String... strings) {
HttpURLConnection c = null;
try {
URL u = new URL("http://api.datausa.io/attrs/geo/"); // use urls first value
c = (HttpURLConnection) u.openConnection();
int status = c.getResponseCode();
switch (status) {
case 200:
case 201:
BufferedReader br = new BufferedReader(new InputStreamReader(c.getInputStream()));
StringBuilder sb = new StringBuilder();
String line;
while ((line = br.readLine()) != null) {
sb.append(line + "\n");
}
br.close();
result = sb.toString();
getValue();
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
if (c != null) {
try {
c.disconnect();
} catch (Exception ex) {
}
}
}
return null;
}
public void getValue() {
// FIX IT
// Parse the JSON properly
}
}
现在了解json解析，数据量巨大，你需要以较小的格式响应这个巨大的json，甚至崩溃在线json格式化程序。 ：）
此代码用于显示所有json。希望这会有所帮助。
答案 1 :(得分：0)
public class Test {
static String Json="{'root':{['ratedetails':{['levelOne':{["+ "{'FGROUP':'A','rentalpackage':'2D','NOOFDAYS':'2', 'HOURS':'0', 'PERIODPRICE':'100.00',"+ "'CUSTOMERPERDAY':'50.00', 'DRIVERPERDAY':'50.00' ,'KMALLOWANCE':'2', 'EXTKMALLOWPDAY':'60',"+ "'DRIVERKMCHARGE':'5', 'CUSTOMERKMCHARGE':'3', 'MAXIMUMKMCHARGE':'99999999', 'MAXKMCHRGTYPE':'0'"+",'HIDDEN':'2'},"+ "{'FGROUP':'A','rentalpackage':'2D','NOOFDAYS':'2', 'HOURS':'0', 'PERIODPRICE':'100.00',"+ "'CUSTOMERPERDAY':'50.00', 'DRIVERPERDAY':'50.00','KMALLOWANCE':'2', 'EXTKMALLOWPDAY':'60',"+ "'DRIVERKMCHARGE':'5', 'CUSTOMERKMCHARGE':'3', 'MAXIMUMKMCHARGE':'99999999', 'MAXKMCHRGTYPE':'0'"+",'HIDDEN':'2'}"+ "]}"+ "]}"+ "]}}";
public static void main(String[] args) {
//new Test().main();
String s[]=Json.split(",");
for(int i=0;i<s.length;i++)
{
if(true){
System.out.println(s[i].split(":")[s[i].split(":").length-2].substring(s[i].split(":")[s[i].split(":").length-2].indexOf("'")+1, s[i].split(":")[s[i].split(":").length-2].lastIndexOf("'"))+" "+ s[i].split(":")[s[i].split(":").length-1].substring(s[i].split(":")[s[i].split(":").length-1].indexOf("'")+1, s[i].split(":")[s[i].split(":").length-1].lastIndexOf("'")));
}
else{
System.out.println(s[i].split(":")[0].replace("'", "").trim()+" "+s[i].split(":")[1].replace("'", "").trim()); } } // System.out.println(Json.split(",")[5].split(":")[1].replace("'", "")); } }