Shorten and expand urls using Google URL Shortener API

GoogleUrl.php

<?php

class GoogleUrl {
	
	const EMPTY_KEY = "Empty Key";
	const EMPTY_URL = "Empty URL";

	private $rest = "https://www.googleapis.com/urlshortener/v1/url";
	private $key = null;
	
	public function __construct( $key = null ){
		$this->setKey( $key );
	}

	public static function create( $key = null ){
		$ins = new self();
		$ins->setKey( $key );
		return $ins;
	}

	public function setKey( $key ){
		$this->key = $key;
	}

	public function shorten( $url ){
		if( empty( $this->key ) ){ throw new Exception( self::EMPTY_KEY ); }
		if( empty( $url ) ){ throw new Exception( self::EMPTY_URL ); }
		$curl = curl_init();
		curl_setopt_array( $curl, array(
			CURLOPT_URL => "{$this->rest}?" . 
				http_build_query( array( "key" => $this->key ) ),
			CURLOPT_HTTPHEADER => array("Content-Type: application/json" ),
			CURLOPT_POST => true,
			CURLOPT_POSTFIELDS => json_encode( array( "longUrl" => $url ) ),
			CURLOPT_RETURNTRANSFER => true
		));
		$res = curl_exec( $curl );
		curl_close( $curl );
		return json_decode($res);
	}

	public function expand( $url ){
		if( empty( $this->key ) ){ throw new Exception( self::EMPTY_KEY ); }
		if( empty( $url ) ){ throw new Exception( self::EMPTY_URL ); }
		$curl = curl_init();
		curl_setopt_array( $curl, array(
			CURLOPT_URL => "{$this->rest}?" . 
				http_build_query(
					array( "key" => $this->key, "shortUrl" => $url)
				),
			CURLOPT_RETURNTRANSFER => true
		));
		$res = curl_exec( $curl );
		curl_close($curl);
		return json_decode( $res );
	}
}


// test 
$gu = GoogleUrl::create( "[your-api-key]" );

try {
	// shorten url
	$shorten = $gu->shorten( "http://www.mach3.jp" );
	var_dump( $shorten );
	// expand the shorten
	$expand = $gu->expand( $shorten->id );
	var_dump( $expand );
} catch( Exception $e ){
	die( $e->getMessage() );
}