PHP 面向对象及Mediawiki 框架分析(二)

mediaHandler可以理解为处理media文件的

/includes/filerepo/file/File.php
/**
* Get a MediaHandler instance for this file
*
* @return MediaHandler|bool Registered MediaHandler for file's MIME
type
* or false if none found
*/
function getHandler() {
if ( !isset( $this->handler ) ) {
$this->handler =
MediaHandler::getHandler( $this->getMimeType() );
}
return $this->handler;
}

getHandler()代码：

includes/media/MediaHandler.php
/**
* Get a MediaHandler for a given MIME type from the instance
cache
*
* @param string $type
* @return MediaHandler
*/
static function getHandler( $type ) {
global $wgMediaHandlers;
if ( !isset( $wgMediaHandlers[$type] ) ) {
wfDebug( __METHOD__ . ": no handler found for $type.\n" );
return false;
}
$class = $wgMediaHandlers[$type];
if ( !isset( self::$handlers[$class] ) ) {
self::$handlers[$class] = new $class;
if ( !self::$handlers[$class]->isEnabled() ) {
self::$handlers[$class] = false;
}
}
return self::$handlers[$class];
}

$class = $wgMediaHandlers[$type];
创建一个MIME-MediaHandler 的类的临时对象。
请看全局变量wgMediaHandlers：

/**
* Plugins for media file type handling.
* Each entry in the array maps a MIME type to a class name
*/
$wgMediaHandlers = array(
'image/jpeg' => 'JpegHandler',
'image/png' => 'PNGHandler',
'image/gif' => 'GIFHandler',
'image/tiff' => 'TiffHandler',
'image/x-ms-bmp' => 'BmpHandler',
'image/x-bmp' => 'BmpHandler',
'image/x-xcf' => 'XCFHandler',
'image/svg+xml' => 'SvgHandler', // official
'image/svg' => 'SvgHandler', // compat
'image/vnd.djvu' => 'DjVuHandler', // official
'image/x.djvu' => 'DjVuHandler', // compat
'image/x-djvu' => 'DjVuHandler', // compat
);

比如JpegHandler：

includes/media/Jpeg.php
class JpegHandler extends ExifBitmapHandler {
function getMetadata( $image, $filename ) {
}
}

请看UML 图：

再看更详细的JpegHandler：
关于thumb 对象的创建，handler 对象在渲染完成thumb 后，执
行dotransform，创建一个thumb 文件对象。以下代码是生成指
令。
Transform()方法的部分代码：

/includes/filerepo/file/File.php
// Actually render the thumbnail...
wfProfileIn( __METHOD__ . '-doTransform' );
$thumb = $handler->doTransform( $this,
$tmpThumbPath, $thumbUrl, $params );
wfProfileOut( __METHOD__ . '-doTransform' );
$tmpFile->bind( $thumb ); // keep alive with $thumb

透过UML 图可以猜测到thumb 对象类是一个
mediatransformoutput 的类型，相比其MIME 类型有关。我们在
MediaHandler 的抽象类中只会看到一个抽象方法而无方法体。

/**
* Get a MediaTransformOutput object representing the
transformed output. Does the
* transform unless $flags contains self::TRANSFORM_LATER.
*
* @param File $image The image object
* @param string $dstPath Filesystem destination path
* @param string $dstUrl Destination URL to use in output
HTML
* @param array $params Arbitrary set of parameters
validated by $this->validateParam()
* Note: These parameters have *not* gone through
$this->normaliseParams()
* @param int $flags A bitfield, may contain
self::TRANSFORM_LATER
* @return MediaTransformOutput
*/
abstract function doTransform( $image, $dstPath,
$dstUrl, $params, $flags = 0 );

再来看JpegHandler UML 图就一目了然。