How to Connect Android to A Remote Server Using JSON, MySQL and PHP

[mm.dubur]

Operating System

Android

Android-MySQL connectivity using JSON and PHP.
INTRODUCTION
To connect android app to a remote server, we use a technology called Volley. Before we start the coding, let’s see some basic theory behind the connection process.
CONCEPT

First the android phone creates a request to the server for asking data. The request contains an address of PHP file. The task of the PHP file is to communicate with the DB and create the list of values in JSON format. There is another advantage of using PHP file that is it gives back-end independence. Back-end independence is nothing but, no matter what front-end coding is used (Android, .NET, Objective C etc…), we no need to change the structure of back-end.
The server then creates a response, packs the JSON values in it and passes it back to the android phone. Normally JSON values will be in form of JSON Array. This is because the values might contain more number of rows, so each row is packed in the array.
STEPS TO BE FOLLOWED
There are four simple steps to be followed to connect MySQL DB to Android. They are
1) Create Request using RequestQueue
2) Create JSONArrayRequest
3) Get JSONObject from JSONArray
4) Add JSONArrayRequest to the request queue

EXPLAINATION OF THE STEPS
1) Create request using RequestQueue
• Before starting the communication, the front-end (android) should create a connection to the back-end. This connection is created using RequestQueue.
• The RequestQueue contains the list of request given by a client, and sends one by one to the server.
2) Create JSONArrayRequest
• Once the RequestQueue sends a request to the server, the server starts to process the request and communicates with the DB and created a list of JSON values.
• These list of values are packed inside one JSONArray.
• The JSONArray is sent to the client.
• The client (Android) receives the JSONArray using JSONArrayRequest.
3) Get JSONObject from JSONArray
• The JSONArray received from the server contains a list of JSONObject.
• In order to process each JSONObject, we have to convert the single JSONArray into list of JSON Objects.
• Once the list of JSON Object is obtained, then it is easy to process them.
4) Add JSOnArrayRequest to RequestQueue.
• The last and the most important step is to add the JSONArrayRequest into RequestQueue.
• If this step is not done, then the Request will never be sent to the server.

CODING
1) Create JSONArrayRequest

1. RequestQueue r;
   
   //this line creates a RequestQueue Object.
   
2. r=
   
   Volley.newRequestQueue
   
   (
   
   this
   
   )
   
   ;
   
   //initialize the RequestQueue.
   

2) Create JSONArrayRequest

1. String
   
   url=
   
   "http://www.vjenterprisevlr.com/phpfiles/readbooks.php"
   
   ;
   
2. JsonArrayRequest jo=
   
   new
   
   JsonArrayRequest(
   
   Request
   
   .Method
   
   .POST
   
   , url, new
   
   Response.Listener
   
   <
   
   JSONArray>
   
   (
   
   )
   
   {
   
   //this line creates a JSONArrayRequest, it passes the url of the PHP file, and specifies that the passing type is POST.
   
3. @Override
   
4. public
   
   void
   
   onResponse(
   
   JSONArray response)
   
   {
   
5. }
   
6. }
   
7. }
   
   , new
   
   Response.ErrorListener
   
   (
   
   )
   
   {
   
8. @Override
   
9. public
   
   void
   
   onErrorResponse(
   
   VolleyError error)
   
   {
   
10. 
    
11. }
    
12. }
    
13. )
    
    ;
    

3) Get JSONObject from JSONArray

1. JSONArray books=
   
   response;
   
2. for
   
   (
   
   int
   
   i=
   
   0
   
   ;
   
   i<
   
   books.length
   
   (
   
   )
   
   ;
   
   i++
   
   )
   
   //create list of JSONObjects from the JSONArray
   
3. {
   
4. try
   
   {
   
5. JSONObject book =
   
   books.getJSONObject
   
   (
   
   i)
   
   ;
   
6. String
   
   bookname=
   
   book.getString
   
   (
   
   "BookName"
   
   )
   
   ;
   
   // get the bookname from JSONObject
   
7. String
   
   price=
   
   book.getString
   
   (
   
   "Price"
   
   )
   
   ;
   
   // get price from JSONObject
   
8. txt.append
   
   (
   
   bookname+
   
   "costs "
   
   +
   
   price+
   
   "\n
   
   "
   
   )
   
   ;
   
   //update output
   
9. }
   
10. catch
    
    (
    
    Exception
    
    e)
    
    //handle any exceptions
    
11. {
    
12. 
    
13. }
    

4) Add JSONArrayRequest to RequestQueue

1. r.add
   
   (
   
   jo)
   
   ;
   
   //add the request into the queue.
   

SOURCE CODE

1. StartPage.java
   
2. package
   
   tutorials.microfusionsmartsolutions.com.volleytest
   
   ;
   
3. 
   
4. import
   
   android.os.Bundle
   
   ;
   
5. import
   
   android.support.v7.app.AppCompatActivity
   
   ;
   
6. import
   
   android.widget.Button
   
   ;
   
7. import
   
   android.widget.TextView
   
   ;
   
8. 
   
9. import
   
   com.android.volley.Request
   
   ;
   
10. import
    
    com.android.volley.RequestQueue
    
    ;
    
11. import
    
    com.android.volley.Response
    
    ;
    
12. import
    
    com.android.volley.VolleyError
    
    ;
    
13. import
    
    com.android.volley.toolbox.JsonArrayRequest
    
    ;
    
14. import
    
    com.android.volley.toolbox.Volley
    
    ;
    
15. 
    
16. import
    
    org.json.JSONArray
    
    ;
    
17. import
    
    org.json.JSONObject
    
    ;
    
18. 
    
19. public
    
    class
    
    StartPage extends
    
    AppCompatActivity {
    
20. 
    
21. Button
    
    but;
    
22. TextView txt;
    
23. RequestQueue r;
    
24. 
    
25. @Override
    
26. protected
    
    void
    
    onCreate(
    
    Bundle savedInstanceState)
    
    {
    
27. super
    
    .onCreate
    
    (
    
    savedInstanceState)
    
    ;
    
28. setContentView(
    
    R.layout
    
    .activity_start_page
    
    )
    
    ;
    
29. but=
    
    (
    
    Button
    
    )
    
    findViewById(
    
    R.id
    
    .button
    
    )
    
    ;
    
30. txt=
    
    (
    
    TextView)
    
    findViewById(
    
    R.id
    
    .textView
    
    )
    
    ;
    
31. String
    
    url=
    
    "http://www.vjenterprisevlr.com/phpfiles/readbooks.php"
    
    ;
    
32. 
    
33. r=
    
    Volley.newRequestQueue
    
    (
    
    this
    
    )
    
    ;
    
34. 
    
35. JsonArrayRequest jo=
    
    new
    
    JsonArrayRequest(
    
    Request
    
    .Method
    
    .POST
    
    , url, new
    
    Response.Listener
    
    <
    
    JSONArray>
    
    (
    
    )
    
    {
    
36. @Override
    
37. public
    
    void
    
    onResponse(
    
    JSONArray response)
    
    {
    
38. JSONArray books=
    
    response;
    
39. for
    
    (
    
    int
    
    i=
    
    0
    
    ;
    
    i<
    
    books.length
    
    (
    
    )
    
    ;
    
    i++
    
    )
    
40. {
    
41. try
    
    {
    
42. JSONObject book =
    
    books.getJSONObject
    
    (
    
    i)
    
    ;
    
43. String
    
    bookname=
    
    book.getString
    
    (
    
    "BookName"
    
    )
    
    ;
    
44. String
    
    price=
    
    book.getString
    
    (
    
    "Price"
    
    )
    
    ;
    
45. txt.append
    
    (
    
    bookname+
    
    "costs "
    
    +
    
    price+
    
    "\n
    
    "
    
    )
    
    ;
    
46. }
    
47. catch
    
    (
    
    Exception
    
    e)
    
48. {
    
49. 
    
50. }
    
51. 
    
52. }
    
53. }
    
54. }
    
    , new
    
    Response.ErrorListener
    
    (
    
    )
    
    {
    
55. @Override
    
56. public
    
    void
    
    onErrorResponse(
    
    VolleyError error)
    
    {
    
57. 
    
58. }
    
59. }
    
60. )
    
    ;
    
61. r.add
    
    (
    
    jo)
    
    ;
    
62. }
    
63. }
    

XML Layout

xml version="1.0" encoding="utf-8"?

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