Tom celic Tom celic - 2 months ago 26
JSON Question

Retrieve JSON Object Android

I'm trying to get a JSON String from a URL but I keep getting a "NetworkOnMainThreadException". I thought I moved my network code to another thread but obviously not.

Here is the error:error

JSONParser

package com.example.jsonparsing;

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.apache.http.params.BasicHttpParams;
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 String getJSONFromUrl(String url) {

DefaultHttpClient httpclient = new DefaultHttpClient(new BasicHttpParams());
HttpPost httppost = new HttpPost("http://api.androidhive.info/contacts/");
// Depends on your web service
httppost.setHeader("Content-type", "application/json");

InputStream inputStream = null;
String result = null;
HttpResponse response = null;
try {
response = httpclient.execute(httppost);
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
HttpEntity entity = response.getEntity();

try {
inputStream = entity.getContent();
} catch (IllegalStateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// json is UTF-8 by default i beleive
BufferedReader reader = null;
try {
reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
StringBuilder sb = new StringBuilder();

String line = null;
try {
while ((line = reader.readLine()) != null)
{
sb.append(line + "\n");
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return result = sb.toString();
}
}


Main Activity

package com.example.jsonparsing;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;

public class MainActivity extends Activity{

// url to make request
private static String url = "http://api.androidhive.info/contacts/";

// contacts JSONArray
JSONArray contacts = null;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

// Hashmap for ListView
ArrayList<HashMap<String, String>> contactList = new ArrayList<HashMap<String, String>>();

RetrieveJSONString retrieveJSON = new RetrieveJSONString();
retrieveJSON.run();
String whatever = retrieveJSON.getJSONString();
}
}

class RetrieveJSONString implements Runnable{

JSONParser jParser;
String jsonString;

public void run() {
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();

// getting JSON string from URL
String jsonString = jParser.getJSONFromUrl("http://api.androidhive.info/contacts/");

}

public String getJSONString(){

return jsonString;
}

}


Manifest

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.jsonparsing"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="15" />
<uses-permission android:name="android.permission.INTERNET"/>

<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/title_activity_main" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>

</manifest>


If anybody can shed some light on the problem I would appreciate it!

Answer

You are getting that error because you are trying to do HTTP calls on the UI-thread, and you should never do that :) Use an AsyncTask instead. Here is a simple example:

GetJsonAsync getJson = new GetJsonAsync();
getJson.execute();

private class GetJsonAsync extends AsyncTask <String, Void, String> {

        @Override
        protected void onPreExecute() {
            // Do stuff before the operation
        }

        @Override
        protected String doInBackground(String... params){
            getJSONFromUrl();
            return null;
        }

        @Override
        protected void onPostExecute(String result) {
            // Do stuff after the operation
        }
    }