设计模式之代理模式

package designPatterns.structuralPatterns.proxy;

import java.util.HashMap;

public interface ThirdPartyYouTubeLib {
    HashMap<String, Video> popularVideos();

    Video getVideo(String videoId);
}

package designPatterns.structuralPatterns.proxy;

import java.util.HashMap;

public class ThirdPartyYouTubeClass implements ThirdPartyYouTubeLib {

    @Override
    public HashMap<String, Video> popularVideos() {
        connectToServer("http://www.youtube.com");
        return getRandomVideos();
    }

    @Override
    public Video getVideo(String videoId) {
        connectToServer("http://www.youtube.com/" + videoId);
        return getSomeVideo(videoId);
    }

    // -----------------------------------------------------------------------
    // Fake methods to simulate network activity. They as slow as a real life.

    private int random(int min, int max) {
        return min + (int) (Math.random() * ((max - min) + 1));
    }

    private void experienceNetworkLatency() {
        int randomLatency = random(5, 10);
        for (int i = 0; i < randomLatency; i++) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }

    private void connectToServer(String server) {
        System.out.print("Connecting to " + server + "... ");
        experienceNetworkLatency();
        System.out.print("Connected!" + "\n");
    }

    private HashMap<String, Video> getRandomVideos() {
        System.out.print("Downloading populars... ");

        experienceNetworkLatency();
        HashMap<String, Video> hmap = new HashMap<String, Video>();
        hmap.put("catzzzzzzzzz", new Video("sadgahasgdas", "Catzzzz.avi"));
        hmap.put("mkafksangasj", new Video("mkafksangasj", "Dog play with ball.mp4"));
        hmap.put("dancesvideoo", new Video("asdfas3ffasd", "Dancing video.mpq"));
        hmap.put("dlsdk5jfslaf", new Video("dlsdk5jfslaf", "Barcelona vs RealM.mov"));
        hmap.put("3sdfgsd1j333", new Video("3sdfgsd1j333", "Programing lesson#1.avi"));

        System.out.print("Done!" + "\n");
        return hmap;
    }

    private Video getSomeVideo(String videoId) {
        System.out.print("Downloading video... ");

        experienceNetworkLatency();
        Video video = new Video(videoId, "Some video title");

        System.out.print("Done!" + "\n");
        return video;
    }

}

package designPatterns.structuralPatterns.proxy;

public class Video {
    public String id;
    public String title;
    public String data;

    Video(String id, String title) {
        this.id = id;
        this.title = title;
        this.data = "Random video.";
    }
}

package designPatterns.structuralPatterns.proxy;

import java.util.HashMap;

public class YouTubeDownloader {
    private ThirdPartyYouTubeLib api;

    public YouTubeDownloader(ThirdPartyYouTubeLib api) {
        this.api = api;
    }

    public void renderVideoPage(String videoId) {
        Video video = api.getVideo(videoId);
        System.out.println("\n-------------------------------");
        System.out.println("Video page (imagine fancy HTML)");
        System.out.println("ID: " + video.id);
        System.out.println("Title: " + video.title);
        System.out.println("Video: " + video.data);
        System.out.println("-------------------------------\n");
    }

    public void renderPopularVideos() {
        HashMap<String, Video> list = api.popularVideos();
        System.out.println("\n-------------------------------");
        System.out.println("Most popular videos on YouTube (imagine fancy HTML)");
        for (Video video : list.values()) {
            System.out.println("ID: " + video.id + " / Title: " + video.title);
        }
        System.out.println("-------------------------------\n");
    }
}

package designPatterns.structuralPatterns.proxy;

import java.util.HashMap;

public class YouTubeCacheProxy implements ThirdPartyYouTubeLib {
    private ThirdPartyYouTubeLib youtubeService;
    private HashMap<String, Video> cachePopular = new HashMap<String, Video>();
    private HashMap<String, Video> cacheAll = new HashMap<String, Video>();

    public YouTubeCacheProxy() {
        this.youtubeService = new ThirdPartyYouTubeClass();
    }

    @Override
    public HashMap<String, Video> popularVideos() {
        if (cachePopular.isEmpty()) {
            cachePopular = youtubeService.popularVideos();
        } else {
            System.out.println("Retrieved list from cache.");
        }
        return cachePopular;
    }

    @Override
    public Video getVideo(String videoId) {
        Video video = cacheAll.get(videoId);
        if (video == null) {
            video = youtubeService.getVideo(videoId);
            cacheAll.put(videoId, video);
        } else {
            System.out.println("Retrieved video '" + videoId + "' from cache.");
        }
        return video;
    }

    public void reset() {
        cachePopular.clear();
        cacheAll.clear();
    }
}

package designPatterns.structuralPatterns.proxy;

/**
 * 代理是一种结构型设计模式， 让你能提供真实服务对象的替代品给客户端使用。
 * 代理接收客户端的请求并进行一些处理 （访问控制和缓存等）， 然后再将请求传递给服务对象。
 *
 * 缓存代理
 * 在本例中， 代理模式有助于实现延迟初始化， 并对低效的第三方 YouTube 集成程序库进行缓存。
 *
 * 当你需要在无法修改代码的类上新增一些额外行为时， 代理模式的价值无可估量。
 */
public class Demo {

    public static void main(String[] args) {
        YouTubeDownloader naiveDownloader = new YouTubeDownloader(new ThirdPartyYouTubeClass());
        YouTubeDownloader smartDownloader = new YouTubeDownloader(new YouTubeCacheProxy());

        long naive = test(naiveDownloader);
        long smart = test(smartDownloader);
        System.out.print("Time saved by caching proxy: " + (naive - smart) + "ms");

    }

    private static long test(YouTubeDownloader downloader) {
        long startTime = System.currentTimeMillis();

        // User behavior in our app:
        downloader.renderPopularVideos();
        downloader.renderVideoPage("catzzzzzzzzz");
        downloader.renderPopularVideos();
        downloader.renderVideoPage("dancesvideoo");
        // Users might visit the same page quite often.
        downloader.renderVideoPage("catzzzzzzzzz");
        downloader.renderVideoPage("someothervid");

        long estimatedTime = System.currentTimeMillis() - startTime;
        System.out.print("Time elapsed: " + estimatedTime + "ms\n");
        return estimatedTime;
    }
}

Connecting to http://www.youtube.com... Connected!
Downloading populars... Done!

-------------------------------
Most popular videos on YouTube (imagine fancy HTML)
ID: sadgahasgdas / Title: Catzzzz.avi
ID: asdfas3ffasd / Title: Dancing video.mpq
ID: 3sdfgsd1j333 / Title: Programing lesson#1.avi
ID: mkafksangasj / Title: Dog play with ball.mp4
ID: dlsdk5jfslaf / Title: Barcelona vs RealM.mov
-------------------------------

Connecting to http://www.youtube.com/catzzzzzzzzz... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: catzzzzzzzzz
Title: Some video title
Video: Random video.
-------------------------------

Connecting to http://www.youtube.com... Connected!
Downloading populars... Done!

-------------------------------
Most popular videos on YouTube (imagine fancy HTML)
ID: sadgahasgdas / Title: Catzzzz.avi
ID: asdfas3ffasd / Title: Dancing video.mpq
ID: 3sdfgsd1j333 / Title: Programing lesson#1.avi
ID: mkafksangasj / Title: Dog play with ball.mp4
ID: dlsdk5jfslaf / Title: Barcelona vs RealM.mov
-------------------------------

Connecting to http://www.youtube.com/dancesvideoo... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: dancesvideoo
Title: Some video title
Video: Random video.
-------------------------------

Connecting to http://www.youtube.com/catzzzzzzzzz... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: catzzzzzzzzz
Title: Some video title
Video: Random video.
-------------------------------

Connecting to http://www.youtube.com/someothervid... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: someothervid
Title: Some video title
Video: Random video.
-------------------------------

Time elapsed: 8954ms
Connecting to http://www.youtube.com... Connected!
Downloading populars... Done!

-------------------------------
Most popular videos on YouTube (imagine fancy HTML)
ID: sadgahasgdas / Title: Catzzzz.avi
ID: asdfas3ffasd / Title: Dancing video.mpq
ID: 3sdfgsd1j333 / Title: Programing lesson#1.avi
ID: mkafksangasj / Title: Dog play with ball.mp4
ID: dlsdk5jfslaf / Title: Barcelona vs RealM.mov
-------------------------------

Connecting to http://www.youtube.com/catzzzzzzzzz... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: catzzzzzzzzz
Title: Some video title
Video: Random video.
-------------------------------

Retrieved list from cache.

-------------------------------
Most popular videos on YouTube (imagine fancy HTML)
ID: sadgahasgdas / Title: Catzzzz.avi
ID: asdfas3ffasd / Title: Dancing video.mpq
ID: 3sdfgsd1j333 / Title: Programing lesson#1.avi
ID: mkafksangasj / Title: Dog play with ball.mp4
ID: dlsdk5jfslaf / Title: Barcelona vs RealM.mov
-------------------------------

Connecting to http://www.youtube.com/dancesvideoo... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: dancesvideoo
Title: Some video title
Video: Random video.
-------------------------------

Retrieved video 'catzzzzzzzzz' from cache.

-------------------------------
Video page (imagine fancy HTML)
ID: catzzzzzzzzz
Title: Some video title
Video: Random video.
-------------------------------

Connecting to http://www.youtube.com/someothervid... Connected!
Downloading video... Done!

-------------------------------
Video page (imagine fancy HTML)
ID: someothervid
Title: Some video title
Video: Random video.
-------------------------------

Time elapsed: 6431ms
Time saved by caching proxy: 2523ms
Process finished with exit code 0