[TOC] ## 概述 **复杂度：** 1星 **流行度：** 3 星 **命令**是一种行为设计模式，它可将请求或简单操作转换为一个对象。 ## 示例 ### 概念示例

main.php

``` payload = $payload; } public function execute(): void { echo "SimpleCommand: See, I can do simple things like printing (" . $this->payload . ")\n"; } } class ComplexCommand implements Command { /** * @var Receiver */ private $receiver; /** * Context data, required for launching the receiver's methods. */ private $a; private $b; /** * @param Receiver $receiver * @param string $a * @param string $b */ public function __construct(Receiver $receiver, string $a, string $b) { $this->receiver = $receiver; $this->a = $a; $this->b = $b; } public function execute(): void { echo "ComplexCommand: Complex stuff should be done by a receiver object.\n"; $this->receiver->doSomething($this->a); $this->receiver->doSomethingElse($this->b); } } class Receiver { public function doSomething(string $a): void { echo "Receiver: Working on (" . $a . ".)\n"; } public function doSomethingElse(string $b): void { echo "Receiver: Also working on (" . $b . ".)\n"; } } class Invoker { /** * @var Command */ private $onStart; /** * @var Command */ private $onFinish; /** * Initialize commands. * @param Command $command */ public function setOnStart(Command $command): void { $this->onStart = $command; } public function setOnFinish(Command $command): void { $this->onFinish = $command; } public function doSomethingImportant(): void { echo "Invoker: Does anybody want something done before I begin?\n"; if ($this->onStart instanceof Command) { $this->onStart->execute(); } echo "Invoker: ...doing something really important...\n"; echo "Invoker: Does anybody want something done after I finish?\n"; if ($this->onFinish instanceof Command) { $this->onFinish->execute(); } } } $invoker = new Invoker(); $invoker->setOnStart(new SimpleCommand("Say Hi!")); $invoker->setOnFinish(new ComplexCommand(new Receiver(), "Send email", "Save report")); $invoker->doSomethingImportant(); ```

输出 ``` Invoker: Does anybody want something done before I begin? SimpleCommand: See, I can do simple things like printing (Say Hi!) Invoker: ...doing something really important... Invoker: Does anybody want something done after I finish? ComplexCommand: Complex stuff should be done by a receiver object. Receiver: Working on (Send email.) Receiver: Also working on (Save report.) ``` ### 网页抓取操作

main.php

``` url = $url; } public function getId(): int { return $this->id; } public function getStatus(): int { return $this->status; } public function getURL(): string { return $this->url; } public function execute(): void { $html = $this->download(); $this->parse($html); $this->complete(); } public function download(): string { $html = file_get_contents($this->getURL()); echo "WebScrapingCommand: Downloaded {$this->url}\n"; return $html; } abstract public function parse(string $html): void; public function complete(): void { $this->status = 1; Queue::get()->completeCommand($this); } } class IMDBGenresScrapingCommand extends WebScrapingCommand { public function __construct() { $this->url = "https://www.imdb.com/feature/genre/"; } public function parse($html): void { preg_match_all("|href=\"(https://www.imdb.com/search/title\?genres=.*?)\"|", $html, $matches); echo "IMDBGenresScrapingCommand: Discovered " . count($matches[1]) . " genres.\n"; foreach ($matches[1] as $genre) { Queue::get()->add(new IMDBGenrePageScrapingCommand($genre)); } } } class IMDBGenrePageScrapingCommand extends WebScrapingCommand { private $page; public function __construct(string $url, int $page = 1) { parent::__construct($url); $this->page = $page; } public function getURL(): string { return $this->url . '?page=' . $this->page; } /** * Extract all movies from a page like this: * https://www.imdb.com/search/title?genres=sci-fi&explore=title_type,genres * @param string $html */ public function parse(string $html): void { preg_match_all("|href=\"(/title/.*?/)\?ref_=adv_li_tt\"|", $html, $matches); echo "IMDBGenrePageScrapingCommand: Discovered " . count($matches[1]) . " movies.\n"; foreach ($matches[1] as $moviePath) { $url = "https://www.imdb.com" . $moviePath; Queue::get()->add(new IMDBMovieScrapingCommand($url)); } // Parse the next page URL. if (preg_match("|Next »|", $html)) { Queue::get()->add(new IMDBGenrePageScrapingCommand($this->url, $this->page + 1)); } } } /** * The Concrete Command for scraping the movie details. */ class IMDBMovieScrapingCommand extends WebScrapingCommand { /** * Get the movie info from a page like this: * https://www.imdb.com/title/tt4154756/ * @param string $html */ public function parse(string $html): void { if (preg_match("|

(.*?)

|", $html, $matches)) { $title = $matches[1]; } echo "IMDBMovieScrapingCommand: Parsed movie $title.\n"; } } class Queue { private $db; public function __construct() { $this->db = new \SQLite3(__DIR__ . '/commands.sqlite', SQLITE3_OPEN_CREATE | SQLITE3_OPEN_READWRITE); $this->db->query('CREATE TABLE IF NOT EXISTS "commands" ( "id" INTEGER PRIMARY KEY AUTOINCREMENT, "command" TEXT NOT NULL DEFAULT \'\', "status" INTEGER NOT NULL DEFAULT 0 );'); } public function isEmpty(): bool { $query = 'SELECT COUNT("id") FROM "commands" WHERE status = 0'; return $this->db->querySingle($query) === 0; } public function add(Command $command): void { $query = 'INSERT INTO commands ("command", "status") VALUES (:command, :status)'; $statement = $this->db->prepare($query); $base64_encode = base64_encode(serialize($command)); $statement->bindValue(':command', $base64_encode); $statement->bindValue(':status', $command->getStatus()); $statement->execute(); } public function getCommand(): Command { $query = 'SELECT * FROM "commands" WHERE "status" = 0 LIMIT 1'; $record = $this->db->querySingle($query, true); $command = unserialize(base64_decode($record["command"])); $command->id = $record['id']; return $command; } public function completeCommand(Command $command): void { $query = 'UPDATE commands SET status = :status WHERE id = :id'; $statement = $this->db->prepare($query); $statement->bindValue(':status', $command->getStatus()); $statement->bindValue(':id', $command->getId()); $statement->execute(); } public function work(): void { while (!$this->isEmpty()) { $command = $this->getCommand(); $command->execute(); } } /** * For our convenience, the Queue object is a Singleton. */ public static function get(): Queue { static $instance; if (!$instance) { $instance = new Queue(); } return $instance; } } /** * The client code. */ $queue = Queue::get(); if ($queue->isEmpty()) { $queue->add(new IMDBGenresScrapingCommand()); } $queue->work(); ```

输出 ``` WebScrapingCommand: Downloaded https://www.imdb.com/feature/genre/ IMDBGenresScrapingCommand: Discovered 14 genres. WebScrapingCommand: Downloaded https://www.imdb.com/search/title?genres=comedy IMDBGenrePageScrapingCommand: Discovered 50 movies. WebScrapingCommand: Downloaded https://www.imdb.com/search/title?genres=sci-fi IMDBGenrePageScrapingCommand: Discovered 50 movies. WebScrapingCommand: Downloaded https://www.imdb.com/search/title?genres=horror IMDBGenrePageScrapingCommand: Discovered 50 movies. WebScrapingCommand: Downloaded https://www.imdb.com/search/title?genres=romance IMDBGenrePageScrapingCommand: Discovered 50 movies. ... ```