Android - Connection to the internet 3

Hello



This post demonstrate client\server interaction using JSON.

The client is android app and the server is asp.net based.

1. Android Client

Java supports JSON in terms of the classes :

• JSONArray
• JSONObject

2. ASP.Net Server
.Net supports JSON in terms of DataContractJsonSerializer




3. Source Sample

JSONClient.zip
JSONWebSite.zip


This sample includes :


1. The client send GET request to an ASP.Net server


2. The server responds with JSON array :

 [ {UserId="John" ,Latitude = 33.33 , Longitude = 44.56 ,Location = "some place 1" },
    {UserId="Jim" ,Latitude = 44.33 , Longitude = 55.56 ,Location = "some place 2" }]
  which is written via  DataContractJsonSerializer and  Response.Write to the client


3. The client parse the JSON array via classes JSONArray and JSONObject and write it to a TextView





Client
uses HttpURLConnection as done in android-connection-to-internet-1

The new stuf here is the parsing of the JSON array

protected void onPostExecute(Object result) {
       try {
       String strOut="";
    JSONArray json = new JSONArray((String)result);
    
    for (int i = 0; i < json.length(); ++i) {
        JSONObject rec = json.getJSONObject(i);
        strOut += String.format("UserId : %s ,Latitude : %f ,Longitude : %f ,Location : %s\n", 
          rec.getString("UserId"),rec.getDouble("Latitude"),
          rec.getDouble("Longitude"),rec.getString("Location"));
       
    }
    textViewMessage.setText(strOut);
       }
    catch (JSONException e) {
    textViewMessage.setText(e.getMessage());
   }
            
       }

MainActivity.java
This is basically like  android-connection-to-internet-1 beside the JSON stuff

package com.example.jsonclient;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;

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

import android.app.Activity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        urlText = (EditText) findViewById(R.id.editTextURL);
        textViewURL = (TextView) findViewById(R.id.textViewURL);
        textViewMessage = (TextView) findViewById(R.id.textViewMessage);
    }

    

    
   // When user clicks button, calls AsyncTask.
   // Before attempting to fetch the URL, makes sure that there is a network connection.
    public void myClickHandler(View view) {
        // Gets the URL from the UI's text field.
        String stringUrl = urlText.getText().toString();
        ConnectivityManager connMgr = (ConnectivityManager) 
            getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            new DownloadWebpageText().execute(stringUrl);
        } else {
            textViewMessage.setText("No network connection available.");
        }
    }

     // Uses AsyncTask to create a task away from the main UI thread. This task takes a 
     // URL string and uses it to create an HttpUrlConnection. Once the connection
     // has been established, the AsyncTask downloads the contents of the web page as
     // an InputStream. Finally, the InputStream is converted into a string, which is
     // displayed in the UI by the AsyncTask's onPostExecute method.
     private class DownloadWebpageText extends AsyncTask {
      @Override
      protected String doInBackground(Object... urls) {
              
            // params comes from the execute() call: params[0] is the url.
            try {
                return downloadUrl((String) urls[0]);
            } catch (IOException e) {
                return "Unable to retrieve web page. URL may be invalid.";
            }
        }
        // onPostExecute displays the results of the AsyncTask.
      @Override
      protected void onPostExecute(Object result) {
       try {
       String strOut="";
    JSONArray json = new JSONArray((String)result);
    
    for (int i = 0; i < json.length(); ++i) {
        JSONObject rec = json.getJSONObject(i);
        strOut += String.format("UserId : %s ,Latitude : %f ,Longitude : %f ,Location : %s\n", 
          rec.getString("UserId"),rec.getDouble("Latitude"),
          rec.getDouble("Longitude"),rec.getString("Location"));
       
    }
    textViewMessage.setText(strOut);
       }
    catch (JSONException e) {
    textViewMessage.setText(e.getMessage());
   }
            
       }
    }
  // Given a URL, establishes an HttpUrlConnection and retrieves
  // the web page content as a InputStream, which it returns as
  // a string.
  private String downloadUrl(String myurl) throws IOException {
      InputStream is = null;
      
           
      try {
          URL url = new URL(myurl);
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setReadTimeout(10000 /* milliseconds */);
          conn.setConnectTimeout(15000 /* milliseconds */);
          conn.setRequestMethod("GET");
          conn.setDoInput(true);
          // Starts the query
          conn.connect();
          int response = conn.getResponseCode();
          Log.d(DEBUG_TAG, "The response is: " + response);
          is = conn.getInputStream();

          // Convert the InputStream into a string
          BufferedReader in = new BufferedReader(new InputStreamReader(is));
         String line;
         String page = "";
         line = in.readLine();
         String  contentAsString="";
         while (line != null)
         {
        contentAsString = contentAsString + line;
           line = in.readLine();
         }
          
          
          return contentAsString;
          
      // Makes sure that the InputStream is closed after the app is
      // finished using it.
      } finally {
          if (is != null) {
              is.close();
          } 
      }
  }
    
//Reads an InputStream and converts it to a String.
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
   Reader reader = null;
   reader = new InputStreamReader(stream, "UTF-8");        
   char[] buffer = new char[len];
   reader.read(buffer);
   return new String(buffer);
}
  
    private static final String DEBUG_TAG = "HttpExample";
    private EditText urlText;
    private TextView textViewURL;
    private TextView textViewMessage;
}

Server

The server is ASP.Net based.
It create JSON array via DataContractJsonSerializer and send to the client using Response.Write .
The server uses helper class name JsonHelper 

main.aspx

CJsonHelper.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.Serialization.Json;
using System.Web;
using System.IO;
using System.Text;  

/// 

/// Summary description for Class1
/// 
public class JsonHelper
{
    /// 

    /// JSON Serialization
    /// 
    public static string JsonSerializer<T>(T t)
    {
        DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(T));
        MemoryStream ms = new MemoryStream();
        ser.WriteObject(ms, t);
        string jsonString = Encoding.UTF8.GetString(ms.ToArray());
        ms.Close();
        return jsonString;
    }
    /// 

    /// JSON Deserialization
    /// 
    public static T JsonDeserialize<T>(string jsonString)
    {
        DataContractJsonSerializer ser = new DataContractJsonSerializer(typeof(T));
        MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(jsonString));
        T obj = (T)ser.ReadObject(ms);
        return obj;
    }
}

CTableRow.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// 

/// Summary description for Class1
/// 
public class CTableRow
{
    public string UserId;
    public double Latitude;
    public double Longitude;
    public string Location;
}

Run the application to create :

Click the Get button to crete

These are the exact info inserted by the server


Nathan