java - 如果网络可用，则从服务器获取 JSON

Question

如何使用负变量值从 Internet 加载文件，以及使用正值变量从手机上的文件加载文件？

它应该像这样工作:

我的系统检查是否有互联网

如果没有，则从内存加载

如果有，则从站点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

这是 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;
}}