JSONObject 创建抛出空指针异常

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【中文标题】JSONObject 创建抛出空指针异常【英文标题】:JSONObject Creation throwing Null Pointer Exception 【发布时间】:2016-12-24 14:01:58 【问题描述】:

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,但是每当我将获得的字符串转换为 JSONObject 时,就会抛出 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这样的:

JSONObject object = new JSONObject(result);

编辑

我被要求放更多源代码,所以这里是(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:如果您想要实时源代码更新,请查看这些文件https://www.dropbox.com/sh/5852rt2rakk6iii/AAAgjsqOTsFfP1N4kS1KzuTBa?dl=0

【问题讨论】:

能否添加代码和字符串。 只需添加一个空检查器。那应该很好。还要确保你实际上得到了任何结果。同时添加结果代码。 空检查器不起作用。 @PritamBanerjee 你能说得更具体点吗? @苏曼达斯 你有线程问题,你想使用尚未获取的 JSON 对象 【参考方案1】:

试图为你做这一切,但让我一步一步为你简化:

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,数据量很大,需要以更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。

【讨论】:

我试过你的方法,还是不行。你认为我应该在 onPostExecute 中完成所有 JSONObject 解析工作吗?对不起,如果我给你带来任何麻烦。 @苏曼达斯 不是问题,是的,您可以在那里完成。试着把代码放在github上让我检查一下,看看是什么问题。 在 GitHub 中创建它时遇到问题,但我在 Dropbox 中创建了一个链接:dropbox.com/sh/5852rt2rakk6iii/AAAgjsqOTsFfP1N4kS1KzuTBa?dl=0@sumandas 在异步任务、连接等方面发现了多个问题。将上传基础知识..并添加详细信息以回答,但您必须自己修复 JSON :( 当 HttpURLConnection 失败时,这仍然会导致相同的 NPE。【参考方案2】:
    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("'", ""));  

【讨论】:

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