Using JSON

The json extension, included by default in PHP installations, natively supports converting data to JSON format from PHP variables and vice versa.

To get a JSON representation of a PHP variable, use json_encode():

$data = array(1, 2, "three");
$jsonData = json_encode($data);
echo $jsonData;
[1, 2, "three"]

Similarly, if you have a string containing JSON data, you can turn it into a PHP variable using json_decode():

$jsonData = "[1, 2, [3, 4], "five"]";
$data = json_decode($jsonData);
print_r($data);
Array( [0] => 1 [1] => 2 [2] => Array( [0] => 3 [1] => 4 ) [3] => five)

If the string is invalid JSON, or if the string is not encoded in UTF-8 format, a single NULL value is returned instead.

The value types in JSON are converted to PHP equivalents as follows:

object

An associative array containing the object’s key-value pairs. Each value is converted into its PHP equivalent as well.

array

An indexed array containing the contained values, each converted into its PHP equivalent as well.

string

Converts directly into a PHP string.

number

Returns a number. If the value is too large to be represented by PHP’s number value, it returns NULL, unless json_decode() is called with the JSON_BIGINT_AS_STRING (in which case, a string is returned).

boolean

The Boolean true value is converted to TRUE; the Boolean false value is converted to FALSE.

null

The null value, and any value that cannot be decoded, is converted to NULL.

Serializing PHP Objects

Despite the similar names, there is no direct translation between PHP objects and JSON objects—what JSON calls an “object” is really an associative array. To convert JSON data into an instance of a PHP object class, you must write code to do so based on the format returned by the API.

However, the JsonSerializable interface allows you to convert objects into JSON data however you like. If an object class does not implement the interface, json_encode() simply creates a JSON object containing keys and values corresponding to the object’s data members.

Otherwise, json_encode() calls the jsonSerialize() method on the class and uses that to serialize the object’s data.

Example 13-1 adds the JsonSerializable interface to the Book and Author classes.

class Book implements JsonSerializable {
 public $id;
 public $name;
 public $edition;

 public function __construct($id) {
 $this->id = $id;
 }

 public function jsonSerialize() {
 $data = array(
 'id' => $this->id,
 'name' => $this->name,
 'edition' => $this->edition,
 );

 return $data;
 }
}

class Author implements JsonSerializable {
 public $id;
 public $name;
 public $books = array();

 public function __construct($id) {
 $this->id = $id;
 }

 public function jsonSerialize() {
 $data = array(
 'id' => $this->id,
 'name' => $this->name,
 'books' => $this->books,
 );

 return $data;
 }
}

Creating a PHP object from JSON data requires you to write code to perform the translation.

Example 13-2 shows a class implementing Factory-style transformation of JSON data into Book and Author instances into PHP objects.

class ResourceFactory {
 static public function authorFromJSON($jsonData) {
 $author = new Author($jsonData['id']);
 $author->name = $jsonData['name'];

 foreach ($jsonData['books'] as $bookIdentifier) {
 $this->books[] = new Book($bookIdentifier);
 }

 return $author;
 }

 static public function bookFromJSON($jsonData) {
 $book = new Book($jsonData['id']);
 $book->name = $jsonData['name'];
 $book->edition = (int) $jsonData['edition'];

 return $book;
 }
}

What’s Next

When you’re writing PHP, one of the most important things to consider is the security of your code, from how well the code can absorb and deflect attacks to how you keep your own and your users’ data safe. The next chapter provides guidance and best practices to help you avert security-related disasters.