JSON Data in PHP REST API

JSON stands for JavaScript Object Notation. It is a lightweight text-based format used to exchange data between applications.

{
    "name": "Rahul",
    "course": "PHP"
}

JSON is easy for both humans and programming languages to read.

REST APIs need a common format for sending data between clients and servers. JSON is widely used for this purpose.

React Native
      ↕
     JSON
      ↕
PHP REST API

The mobile application can send JSON to PHP and PHP can return JSON to the mobile application.

A JSON object contains data in key-value pairs.

{
    "name": "Rahul",
    "email": "rahul@example.com",
    "course": "PHP"
}

The keys are written inside double quotes.

A JSON array can contain multiple values or objects.

[
    {
        "id": 1,
        "name": "Rahul"
    },
    {
        "id": 2,
        "name": "Amit"
    }
]

Arrays are useful when an API returns multiple records.

PHP provides built-in functions for working with JSON.

• json_encode() converts PHP data to JSON.
• json_decode() converts JSON to PHP data.

PHP Array
   ↓
json_encode()
   ↓
JSON

JSON
   ↓
json_decode()
   ↓
PHP Array

The json_encode() function converts PHP data into a JSON string.

$student = [
    "name" => "Rahul",
    "course" => "PHP"
];

echo json_encode($student);

The output is:

{"name":"Rahul","course":"PHP"}

When a PHP API returns JSON, set the response content type.

header("Content-Type: application/json");

This tells the client that the response contains JSON data.

<?php

header("Content-Type: application/json");

$response = [
    "success" => true,
    "message" => "API is working"
];

echo json_encode($response);

?>

The API returns a JSON object containing a success value and message.

The json_decode() function converts JSON into PHP data.

$json = '{
    "name": "Rahul",
    "course": "PHP"
}';

$data = json_decode($json, true);

The second parameter true makes the result an associative array.

After decoding JSON into an associative array, values can be accessed using their keys.

echo $data['name'];

echo $data['course'];

The output will be:

Rahul
PHP

A REST API can receive JSON through the HTTP request body.

$input = file_get_contents(
    "php://input"
);

This reads the raw body sent by the client.

The raw JSON body can be converted into a PHP associative array.

$data = json_decode(
    file_get_contents("php://input"),
    true
);

Now the PHP code can work with the received values.

A React Native application or Postman can send:

{
    "name": "Rahul",
    "email": "rahul@example.com",
    "mobile": "9876543210",
    "course": "PHP"
}

PHP receives this JSON through the request body.

$data = json_decode(
    file_get_contents("php://input"),
    true
);

$name = $data['name'];
$email = $data['email'];
$mobile = $data['mobile'];
$course = $data['course'];

Each JSON property can now be accessed using PHP array syntax.

The null coalescing operator can be used when a JSON key may not exist.

$name = $data['name'] ?? '';
$email = $data['email'] ?? '';
$mobile = $data['mobile'] ?? '';
$course = $data['course'] ?? '';

If a key does not exist, an empty string is used.

The API should validate the received data before processing it.

if ($name === '' || $email === '') {

    http_response_code(400);

    echo json_encode([
        "success" => false,
        "message" => "Name and email are required"
    ]);

    exit;
}

When sending JSON to an API, the client should identify the content type.

Content-Type: application/json

This tells the server that the request body contains JSON data.

PHP can return a student array as JSON.

$student = [
    "id" => 1,
    "name" => "Rahul",
    "email" => "rahul@example.com",
    "course" => "PHP"
];

echo json_encode($student);

Multiple PHP records can be converted into a JSON array.

$students = [
    [
        "id" => 1,
        "name" => "Rahul"
    ],
    [
        "id" => 2,
        "name" => "Amit"
    ]
];

echo json_encode($students);

A REST API can wrap the data inside a response object.

$response = [
    "success" => true,
    "message" => "Students fetched successfully",
    "data" => $students
];

echo json_encode($response);

This makes the response easier for clients to understand.

Errors can also be returned as JSON.

http_response_code(400);

echo json_encode([
    "success" => false,
    "message" => "Invalid request"
]);

The client can check the HTTP status and JSON message.

Database records can be fetched using PDO and then converted to JSON.

$stmt = $pdo->query(
    "SELECT id, name, email, mobile, course
     FROM students"
);

$students = $stmt->fetchAll(
    PDO::FETCH_ASSOC
);

echo json_encode([
    "success" => true,
    "data" => $students
]);

React Native
      ↓
JSON Request
      ↓
php://input
      ↓
json_decode()
      ↓
PHP Array
      ↓
MySQL
      ↓
PHP Array
      ↓
json_encode()
      ↓
JSON Response
      ↓
React Native

Postman can be used to test JSON requests.

Choose:

Method: POST

Body:
raw
JSON

Then enter:

{
    "name": "Rahul",
    "email": "rahul@example.com",
    "mobile": "9876543210",
    "course": "PHP"
}

If the client sends invalid JSON, json_decode() may not produce the expected PHP data.

For example, this is invalid JSON:

{
    "name": "Rahul",
    "email": "rahul@example.com",
}

There is an extra comma after the email value.

PHP provides json_last_error() to check the last JSON decoding or encoding error.

$data = json_decode(
    $input,
    true
);

if (json_last_error() !== JSON_ERROR_NONE) {

    echo json_encode([
        "success" => false,
        "message" => "Invalid JSON"
    ]);

    exit;
}

React Native can send JSON using JSON.stringify().

fetch("http://localhost/rest_api/api/students.php", {
    method: "POST",
    headers: {
        "Content-Type": "application/json"
    },
    body: JSON.stringify({
        name: "Rahul",
        email: "rahul@example.com",
        mobile: "9876543210",
        course: "PHP"
    })
});

The PHP API can receive this data using php://input.

React Native can convert a JSON HTTP response into JavaScript data using response.json().

fetch("http://localhost/rest_api/api/students.php")
    .then(response => response.json())
    .then(data => {
        console.log(data);
    });

This allows the application to work with the API response.

• Use valid JSON syntax.
• Use double quotes around JSON keys and string values.
• Set the correct Content-Type.
• Validate incoming JSON data.
• Use json_decode() for incoming JSON.
• Use json_encode() for outgoing JSON.
• Return consistent response structures.
• Do not expose sensitive information.

JSON is the main data exchange format we are using between our PHP REST API and React Native application. PHP uses json_decode() to read JSON received from the client and json_encode() to send PHP data back as JSON.

Client
  ↓
JSON
  ↓
json_decode()
  ↓
PHP
  ↓
MySQL
  ↓
PHP
  ↓
json_encode()
  ↓
JSON
  ↓
Client