JSON解析Android [重复]答案

【问题标题】：JSON Parsing Android [duplicate]JSON解析Android [重复]
【发布时间】：2014-01-22 04:05:45
【问题描述】：

我还是一个android web service的初学者，现在我从url解析json数据遇到了问题。

这里是我的代码： JSONParser.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import android.util.Log;
public class JSONParser {
static InputStream is = null;
static JSONObject jObj = null;
static String json = "";
// constructor
public JSONParser() {
}
public JSONObject getJSONFromUrl(String url) {
    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();
    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "UTF-8"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }
    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    // return JSON String
    return jObj;
 }
}

这里是我的 MainActivity.java

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import learn2crack.jsonparsing.library.JSONParser;
public class MainActivity extends Activity {
//URL to get JSON Array
private static String url = "https://api.themoviedb.org/3/genre/list?api_key=d397dd2d354f088c6f0eb91c6b160bb0";
//JSON Node Names
private static final String TAG_GENRES = "genres";
private static final String TAG_ID = "id";
private static final String TAG_NAME = "name";

JSONArray genres = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // Creating new JSON Parser
    JSONParser jParser = new JSONParser();
    // Getting JSON from URL
    JSONObject json = jParser.getJSONFromUrl(url);
    try {
        // Getting JSON Array
        genres = json.getJSONArray(TAG_GENRES);
        JSONObject c = genres.getJSONObject(0);
        // Storing  JSON item in a Variable
        String id = c.getString(TAG_ID);
        String name = c.getString(TAG_NAME);

        //Importing TextView
        final TextView uid = (TextView)findViewById(R.id.uid);
        final TextView name1 = (TextView)findViewById(R.id.name);

        //Set JSON Data in TextView
        uid.setText(id);
        name1.setText(name);

} catch (JSONException e) {
    e.printStackTrace();
   }
  }
}

但我在 logcat 中收到错误，如下所示

01-22 10:36:09.701: E/JSON Parser(379): Error parsing data org.json.JSONException: Value <h1>Not of type java.lang.String cannot be converted to JSONObject
01-22 10:36:09.721: E/AndroidRuntime(379): FATAL EXCEPTION: main
01-22 10:36:09.721: E/AndroidRuntime(379): java.lang.RuntimeException: Unable to start activity ComponentInfo{learn2crack.jsonparsing/learn2crack.jsonparsing.MainActivity}: java.lang.NullPointerException
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.os.Handler.dispatchMessage(Handler.java:99)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.os.Looper.loop(Looper.java:130)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.app.ActivityThread.main(ActivityThread.java:3683)
01-22 10:36:09.721: E/AndroidRuntime(379):  at java.lang.reflect.Method.invokeNative(Native Method)
01-22 10:36:09.721: E/AndroidRuntime(379):  at java.lang.reflect.Method.invoke(Method.java:507)
01-22 10:36:09.721: E/AndroidRuntime(379):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-22 10:36:09.721: E/AndroidRuntime(379):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-22 10:36:09.721: E/AndroidRuntime(379):  at dalvik.system.NativeStart.main(Native Method)
01-22 10:36:09.721: E/AndroidRuntime(379): Caused by: java.lang.NullPointerException
01-22 10:36:09.721: E/AndroidRuntime(379):  at learn2crack.jsonparsing.MainActivity.onCreate(MainActivity.java:29)
01-22 10:36:09.721: E/AndroidRuntime(379):  at  android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-22 10:36:09.721: E/AndroidRuntime(379):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

这是我的 json 数据

{"genres":[{"id":28,"name":"Action"},{"id":12,"name":"Adventure"},{"id":16,"name":"Animation"},{"id":35,"name":"Comedy"},{"id":80,"name":"Crime"},{"id":105,"name":"Disaster"},{"id":99,"name":"Documentary"},{"id":18,"name":"Drama"},{"id":82,"name":"Eastern"},{"id":2916,"name":"Erotic"},{"id":10751,"name":"Family"},{"id":10750,"name":"Fan Film"},{"id":14,"name":"Fantasy"},{"id":10753,"name":"Film Noir"},{"id":10769,"name":"Foreign"},{"id":36,"name":"History"},{"id":10595,"name":"Holiday"},{"id":27,"name":"Horror"},{"id":10756,"name":"Indie"},{"id":10402,"name":"Music"},{"id":22,"name":"Musical"},{"id":9648,"name":"Mystery"},{"id":10754,"name":"Neo-noir"},{"id":1115,"name":"Road Movie"},{"id":10749,"name":"Romance"},{"id":878,"name":"Science Fiction"},{"id":10755,"name":"Short"},{"id":9805,"name":"Sport"},{"id":10758,"name":"Sporting Event"},{"id":10757,"name":"Sports Film"},{"id":10748,"name":"Suspense"},{"id":10770,"name":"TV movie"},{"id":53,"name":"Thriller"},{"id":10752,"name":"War"},{"id":37,"name":"Western"}]}

我仍然对上述解决方案感到困惑，有人可以帮忙吗？

【问题讨论】：

你在 Main Activity 中的第 29 行是哪一行？
先放到线程中
@user3197499 我非常不愿意回答你的问题，因为很多答案都投了反对票。这个框也太小了，无法讨论您的所有问题：您确定您的 JSONObject json 不为空吗？你确定你的意思是在你的主线程上有一个很长的网络请求吗？安卓不喜欢这样。 PS - “谢谢兄弟”。
@user3197499 看起来你也在这里尝试过：stackoverflow.com/questions/21273950/json-parsing-android
@user3197499 请阅读此内容。 en.wikipedia.org/wiki/Hypertext_Transfer_Protocol

标签： java android json parsing nullpointerexception

【解决方案1】：

 HttpGet httpPost = new HttpGet(url);

【讨论】：

请点赞并标记为 ri8

【解决方案2】：

您声称要解析的 JSON 不是您要解析的。

您从jObj = new JSONObject(json); 捕获异常并记录它；它告诉您在您要解析的字符串的开头有一个<h1>。然后您返回jObj，它仍然是null，因此当您尝试使用它时，您的应用程序会以NullPointerException 退出。

这是因为您正在对服务器执行POST：

HttpPost httpPost = new HttpPost(url);

如果您要打印出您会找到的结果，则会返回：

<h1>Not Found</h1>

你需要做一个GET

HttpGet httpGet = new HttpGet(url);

在尝试调试某些东西时，验证您的输入总是一个好主意。

【讨论】：

在 OP 出于无知投反对票之前，对您的帖子投了赞成票。（而且因为它完全正确。）
@SK9 我离开了几个小时，显然错过了所有的乐趣/戏剧？
@Brian Roach 你有解决方案源代码来解析这个 url api.themoviedb.org/3/genre/18/… 的 json 数据。我尝试但模拟器没有响应。

【解决方案3】：

您似乎正在放置一个长时间运行的进程，即在主线程上进行网络通信。你不被允许这样做。你可以使用 AsyncTask

http://developer.android.com/reference/android/os/AsyncTask.html

此外，这里有一个很好的视频，它解释了使用 AsyncTask 进行 JSON 解析。

http://www.youtube.com/watch?v=qcotbMLjlA4

只是为了测试，您可以在 Main Activity 中添加以下内容，但这被认为是不好的做法。

StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);

【讨论】：

我可以知道为什么投反对票吗？
@user3197499 虽然这不能回答 OP 的问题，但它确实提供了合理的建议。
兄弟什么意思？

【解决方案4】：

您的 JSON 对象返回“null”，这就是您收到 nullpointer 异常的原因。您必须使用“GET”而不是“POST”。试试这个代码

public JSONObject getJSONFromUrl(String jurl) {
    // Making HTTP request


    String marketUrl =jurl;             
    URL url;                
    try {
            url = new URL(marketUrl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10000);
            conn.setConnectTimeout(15000);
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Content-length", "0");
            conn.setAllowUserInteraction(false);
            // Starts the query
            conn.connect();
            int status = conn.getResponseCode();
            StringBuilder sb = new StringBuilder();
            switch (status) {
            case 200:
            case 201:
                BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                String line;
                while ((line = br.readLine()) != null) {
                    sb.append(line+"\n");
                }
                br.close();
                String responseData = sb.toString();      
                jObj = new JSONObject(responseData);
    } 
    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (JSONException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    return jObj;
 }
}

【讨论】：