Saumitra Mhapankar Saumitra Mhapankar - 5 months ago 9
Android Question

How can I fetch data from a web server in an android application?

I want to retrieve data from a web server in an android application, and don't know where to begin. Should I use web services?

Answer

I would recommend these tutorials:

Connect android with PHP and MySql, JSON in android and PHP and MySQLi

I used these tutorials and managed to get what you are trying to do working without too much difficulty.

Between them they describe each step in how to do what you are attempting at each stage, the android application, the database and the web server side and has extra information included for what you can then do to process and use the received information

The only thing I would add is that the Connect android with PHP and MySql tutorial makes use of mysql_ in php which is deprecated. Much better to use MySqli which is why I included the third link.

The basic outline of what you want to do is this:

1) in the android app make a request to a server php script using a class like this:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.utils.URLEncodedUtils;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;

import android.util.Log;

public class JSONParser {

    // Response from the HTTP Request
    static InputStream httpResponseStream = null;
    // JSON Response String to create JSON Object
    static String jsonString = "";

    // Method to issue HTTP request, parse JSON result and return JSON Object
    public JSONObject makeHttpRequest(String url, String method,
            List<NameValuePair> params) {

        try {
            // get a Http client
            DefaultHttpClient httpClient = new DefaultHttpClient();

            // If required HTTP method is POST
            if (method == "POST") {
                // Create a Http POST object
                HttpPost httpPost = new HttpPost(url);
                // Encode the passed parameters into the Http request
                httpPost.setEntity(new UrlEncodedFormEntity(params));
                // Execute the request and fetch Http response
                HttpResponse httpResponse = httpClient.execute(httpPost);
                // Extract the result from the response
                HttpEntity httpEntity = httpResponse.getEntity();
                // Open the result as an input stream for parsing
                httpResponseStream = httpEntity.getContent();
            }
            // Else if it is GET
            else if (method == "GET") {
                // Format the parameters correctly for HTTP transmission
                String paramString = URLEncodedUtils.format(params, "utf-8");
                // Add parameters to url in GET format
                url += "?" + paramString;
                // Execute the request
                HttpGet httpGet = new HttpGet(url);
                // Execute the request and fetch Http response
                HttpResponse httpResponse = httpClient.execute(httpGet);
                // Extract the result from the response
                HttpEntity httpEntity = httpResponse.getEntity();
                // Open the result as an input stream for parsing
                httpResponseStream = httpEntity.getContent();
            }
            // Catch Possible Exceptions
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            // Create buffered reader for the httpResponceStream
            BufferedReader httpResponseReader = new BufferedReader(
                    new InputStreamReader(httpResponseStream, "iso-8859-1"), 8);
            // String to hold current line from httpResponseReader
            String line = null;
            // Clear jsonString
            jsonString = "";
            // While there is still more response to read
            while ((line = httpResponseReader.readLine()) != null) {
                // Add line to jsonString
                jsonString += (line + "\n");
            }
            // Close Response Stream
            httpResponseStream.close();
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        try {
            // Create jsonObject from the jsonString and return it
            return new JSONObject(jsonString);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
            // Return null if in error
            return null;
        }
    }
}

Which handles communication, opens a connection and receives a JSON string which it then processes into a JSON object.

2) in the php server, open an mysqli connection to your SQL database, run an mysqli->query() and do something like the following with the result:

if (mysqli_num_rows($result) > 0) {
        // looping through all results
        $response["apps"] = array();

        while ($row = mysqli_fetch_array($result)) {

            $apps = array();

            $apps["name"] = $row["name"];
            $apps["package"] = $row["package"];
            $apps["version"] = $row["version"];
            $apps["dateversion"] = $row["dateversion"];
            $apps["sdkver"] = $row["sdkver"];
            $apps["pathroot"] = $row["pathroot"];
            $apps["rootname"] = $row["rootname"];
            $apps["apkmd5"] = $row["apkmd5"];
            $apps["extraapkmd5"] = $row["extraapkmd5"];
            $apps["instructionsmd5"] = $row["instructionsmd5"];
            $apps["assetsmd5"] = $row["assetsmd5"];
            $apps["root"] = $row["root"];
            $apps["current"] = $row["current"];

            // push single product into final response array
            array_push($response["apps"], $apps);
        }
        // success
        $response["success"] = 1;

        // echoing JSON response
        echo json_encode($response);

This iterates through the database response and encodes it into a JSON string which is sent back to the android app which can then process it.

How to create something like this is all explained in the tutorials linked

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