如果网络可用，java从服务器获取JSON

Question

如何从互联网上加载变量为负值的文件，以及从手机上加载变量为正值的文件

它应该是这样工作的：

我的系统检查是否有互联网

如果不是，则从内存加载

如果有，请从站点url加载

public String getJSONFromAssets(Context context) {
        String json = null;
        try {
            InputStream inputData = context.getAssets().open("data.json"); //load assets file
            //Log.e("100rad", ":"+inputData);
            int size = inputData.available();
            byte[] buffer = new byte[size];
            inputData.read(buffer);
            inputData.close();
            json = new String(buffer, "UTF-8");
        } catch (IOException ex) {
            ex.printStackTrace();
            return null;
        }
        return json;
    }
    private class AsyncTaskGetMareker extends AsyncTask<String , String, JSONArray> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected JSONArray doInBackground(String... strings) {
            String stationsJsonString = getJSONFromAssets(MainActivity.this);
            try {
                JSONArray stationsJsonArray = new JSONArray(stationsJsonString);
                return stationsJsonArray;
            } catch (JSONException e) {
                e.printStackTrace();
            }
            //This will only happen if an exception is thrown above:
            return null;
        }

        protected void onPostExecute (JSONArray result){
            if (result !=null){
                for (int i =0; i <result.length(); i++){
                    JSONObject jsonObject= null;
                    try {
                        jsonObject= result.getJSONObject(i);
                        String name=jsonObject.getString("store_name");
                        String lat=jsonObject.getString("latitude");
                        String lang=jsonObject.getString("longitude");
                        String desc=jsonObject.getString("store_desc");
                        String oxr=jsonObject.getString("telephone");
                        String sost=jsonObject.getString("keywords");
                        int cat=jsonObject.getInt("category_id");
                        int id=jsonObject.getInt("id");
} catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }

Answer 1

您也可以添加此支票

public static boolean isNetworkAvailable(Context con) {
        try {
            ConnectivityManager cm = (ConnectivityManager) con
                    .getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo = cm.getActiveNetworkInfo();

            if (networkInfo != null && networkInfo.isConnected()) {
                return true;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }

然后在你的活动/片段中检查这个

if (isNetworkAvailable)
{
//Do you task
//callAPI(); fetch data from website / api call
}
else{
/*No internet so, load from memory */
}

Answer 2

您可以通过以下代码检查您的移动设备是否连接到互联网

public class ConnectionDetector
{
private Context _context;
public ConnectionDetector(Context context)
{
    this._context = context;
}
public  boolean isConnectingToInternet()
{
    ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);
    if (connectivity != null)
    {
        NetworkInfo info = connectivity.getActiveNetworkInfo();
        if (info != null)
        {
            if (info.getType() == ConnectivityManager.TYPE_WIFI)
            {
                return true;
            }
            else if (info.getType() == ConnectivityManager.TYPE_MOBILE)
            {
                return true;
            }
        }
        else
        {
            // not connected to the internet
            return false;
        }
    }
    return false;
}}

您的AsyncTask类代码类似于下面的代码

private class AsyncTaskGetMareker extends AsyncTask<String , String, JSONArray> 
 {
@Override
protected void onPreExecute() {
    super.onPreExecute();
}

@Override
protected JSONArray doInBackground(String... strings) {
     JSONArray stationsJsonArray;
    String stationsJsonString = getJSONFromAssets(MainActivity.this);
    try {
         if(new ConnectionDetector().isConnectionToInternet())
         {
            Hashmap<String,String> mapToSend = new Hashmap();
         JSONParser jsonParser = new JSONParser();

          stationsJsonArray = jsonParser.makeHttpRequest("URL", "POST", mapToSend);

         }else{
           stationsJsonArray = new JSONArray(stationsJsonString);
         }

        return stationsJsonArray;
    } catch (JSONException e) {
        e.printStackTrace();
    }
    //This will only happen if an exception is thrown above:
    return null;
}

protected void onPostExecute (JSONArray result){
    if (result !=null){
        for (int i =0; i <result.length(); i++){
            JSONObject jsonObject= null;
            try {
                jsonObject= result.getJSONObject(i);
                String name=jsonObject.getString("store_name");
                String lat=jsonObject.getString("latitude");
                String lang=jsonObject.getString("longitude");
                String desc=jsonObject.getString("store_desc");
                String oxr=jsonObject.getString("telephone");
                String sost=jsonObject.getString("keywords");
                int cat=jsonObject.getInt("category_id");
                int id=jsonObject.getInt("id");
         } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }
}

}

Answer 3

下面是JSONParser类

import android.util.Log;

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

 import java.io.BufferedInputStream;
 import java.io.BufferedReader;
 import java.io.DataOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.UnsupportedEncodingException;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.net.URLEncoder;
 import java.util.HashMap;

 public class JSONParser {

String charset = "UTF-8";
HttpURLConnection conn;
DataOutputStream wr;
StringBuilder result;
URL urlObj;
JSONObject jObj = null;
StringBuilder sbParams;
String paramsString;

public JSONObject makeHttpRequest(String url, String method,
                                  HashMap<String, String> params) {

    sbParams = new StringBuilder();
    int i = 0;
    for (String key : params.keySet()) {
        try {
            if (i != 0){
                sbParams.append("&");
            }
            sbParams.append(key).append("=")
                    .append(URLEncoder.encode(params.get(key), charset));

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        i++;
    }

    if (method.equals("POST")) {
        // request method is POST
        try {
            urlObj = new URL(url);

            conn = (HttpURLConnection) urlObj.openConnection();

            conn.setDoOutput(true);

            conn.setRequestMethod("POST");

            conn.setRequestProperty("Accept-Charset", charset);

            conn.setReadTimeout(10000);
            conn.setConnectTimeout(15000);

            conn.connect();

            paramsString = sbParams.toString();

            wr = new DataOutputStream(conn.getOutputStream());
            wr.writeBytes(paramsString);
            wr.flush();
            wr.close();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    else if(method.equals("GET")){
        // request method is GET

        if (sbParams.length() != 0) {
            url += "?" + sbParams.toString();
        }

        try {
            urlObj = new URL(url);

            conn = (HttpURLConnection) urlObj.openConnection();

            conn.setDoOutput(false);

            conn.setRequestMethod("GET");

            conn.setRequestProperty("Accept-Charset", charset);

            conn.setConnectTimeout(15000);

            conn.connect();

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

    }

    try {
        //Receive the response from the server
        InputStream in = new BufferedInputStream(conn.getInputStream());
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        result = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }

        Log.d("JSON Parser", "result: " + result.toString());

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

    conn.disconnect();

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(result.toString());
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    // return JSON Object
    return jObj;
}}