Factory method design patten in PHP

Jan 23, 2010 Design patterns PHP

An creational design pattern, which represents an solution for generation objects without specifying the class name. Virtually all methods that generate objects are particular implementations of the Factory Method pattern.

Motivation:

A motivation for this choice is that the creation of the object is delegated to the factory method.

Diagram:

factory method pattern

Implementation:
The classes that generates the objects, the common class to extend and the class with the factory method:

  1// the common class to be extended
  2abstract class OutputBase {
  3     // output the necessary headers
  4     abstract public function header();
  5
  6     // resulting body
  7     abstract public function body($data);
  8
  9}
 10
 11// class for XML ouput
 12class XMLOutput extends OutputBase {
 13
 14     // output XML header
 15     public function header() {
 16          header('content-type: text/xml');
 17     }
 18
 19     // xml document
 20     public function body($data) {
 21          $res = '';
 22
 23          $res .= '';
 24
 25          foreach ($data as $root => $item) {
 26
 27               $res .= '';
 28
 29               foreach ($item as $key => $val) {
 30                    $res .= '<'.$key.'>'.$val.'';
 31               }
 32
 33               $res .= '';
 34          }
 35
 36          $res .= '';
 37
 38          return $res;
 39
 40     }
 41
 42}
 43
 44// class for CSV output
 45class CSVOutput extends OutputBase {
 46
 47     // output CSV header
 48     public function header() {
 49          header("Content-type: text/plain");
 50     }
 51
 52     // CSV body
 53     public function body($data) {
 54          $res = '';
 55
 56          $keys = array_keys($data[0]);
 57
 58          foreach ($keys as $key) {
 59               $res .= '"'.$key.'";';
 60          }
 61          $res .= "\r\n";
 62
 63          foreach ($data as $item) {
 64               foreach ($item as $val) {
 65                    $res .= '"'.$val.'";';
 66               }
 67
 68               $res .= "\r\n";
 69          }
 70
 71          return $res;
 72     }
 73}
 74
 75// the factory method class
 76// is abstract so it wont be instantiated
 77abstract class OutputFactory {
 78
 79     // constant for XML type
 80     const XML = 1;
 81
 82     // constant for CSV type
 83     const CSV = 2;
 84
 85     // static factory method
 86     public static function getInstance($type) {
 87          // depending which constant was received as a parameter
 88          // one of the objects will be returned
 89          switch ($type) {
 90               case self::XML :
 91                    return new XMLOutput();
 92               break;
 93
 94               case self::CSV :
 95                    return new CSVOutput();
 96               break;
 97          }
 98
 99          // if the value received as a parameter is not one of the constants
100          // an exception will be thrown
101          throw new Exception('Invalid class type!');
102     }
103
104}

Example:

 1// the data
 2$data = array(
 3               array(
 4                    'a' => 1,
 5                    'b' => 2,
 6                    'c' => 3
 7                    ),
 8               array(
 9                    'a' => 4,
10                    'b' => 5,
11                    'c' => 6
12                    )
13          );
14
15// try-catch block in case of an exception
16try {
17     // generation the object
18     $obj = OutputFactory::getInstance(OutputFactory::XML);
19
20     // output headers
21     $obj->header();
22
23     // display body
24     echo $obj->body($data);
25
26} catch (Exception $e) {
27
28     $e->getMessage();
29
30}