23种设计模式之观察者模式-Observer

// 发布者基类包含订阅管理代码和通知方法。
class EventManager is
    private field listeners: hash map of event types and listeners

    method subscribe(eventType, listener) is
        listeners.add(eventType, listener)

    method unsubscribe(eventType, listener) is
        listeners.remove(eventType, listener)

    method notify(eventType, data) is
        foreach (listener in listeners.of(eventType)) do
            listener.update(data)

// 具体发布者包含一些订阅者感兴趣的实际业务逻辑。我们可以从发布者基类中扩
// 展出该类，但在实际情况下并不总能做到，因为具体发布者可能已经是子类了。
// 在这种情况下，你可用组合来修补订阅逻辑，就像我们在这里做的一样。
class Editor is
    public field events: EventManager
    private field file: File

    constructor Editor() is
        events = new EventManager()

    // 业务逻辑的方法可将变化通知给订阅者。
    method openFile(path) is
        this.file = new File(path)
        events.notify("open", file.name)

    method saveFile() is
        file.write()
        events.notify("save", file.name)

    // ...


// 这里是订阅者接口。如果你的编程语言支持函数类型，则可用一组函数来代替整
// 个订阅者的层次结构。
interface EventListener is
    method update(filename)

// 具体订阅者会对其注册的发布者所发出的更新消息做出响应。
class LoggingListener implements EventListener is
    private field log: File
    private field message

    constructor LoggingListener(log_filename, message) is
        this.log = new File(log_filename)
        this.message = message

    method update(filename) is
        log.write(replace('%s',filename,message))

class EmailAlertsListener implements EventListener is
    private field email: string

    constructor EmailAlertsListener(email, message) is
        this.email = email
        this.message = message

    method update(filename) is
        system.email(email, replace('%s',filename,message))


// 应用程序可在运行时配置发布者和订阅者。
class Application is
    method config() is
        editor = new Editor()

        logger = new LoggingListener(
            "/path/to/log.txt",
            "有人打开了文件：%s");
        editor.events.subscribe("open", logger)

        emailAlerts = new EmailAlertsListener(
            "admin@example.com",
            "有人更改了文件：%s")
        editor.events.subscribe("save", emailAlerts)

package refactoring_guru.observer.example.publisher;

import refactoring_guru.observer.example.listeners.EventListener;

import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class EventManager {
    Map<String, List<EventListener>> listeners = new HashMap<>();

    public EventManager(String... operations) {
        for (String operation : operations) {
            this.listeners.put(operation, new ArrayList<>());
        }
    }

    public void subscribe(String eventType, EventListener listener) {
        List<EventListener> users = listeners.get(eventType);
        users.add(listener);
    }

    public void unsubscribe(String eventType, EventListener listener) {
        List<EventListener> users = listeners.get(eventType);
        users.remove(listener);
    }

    public void notify(String eventType, File file) {
        List<EventListener> users = listeners.get(eventType);
        for (EventListener listener : users) {
            listener.update(eventType, file);
        }
    }
}

package refactoring_guru.observer.example.editor;

import refactoring_guru.observer.example.publisher.EventManager;

import java.io.File;

public class Editor {
    public EventManager events;
    private File file;

    public Editor() {
        this.events = new EventManager("open", "save");
    }

    public void openFile(String filePath) {
        this.file = new File(filePath);
        events.notify("open", file);
    }

    public void saveFile() throws Exception {
        if (this.file != null) {
            events.notify("save", file);
        } else {
            throw new Exception("Please open a file first.");
        }
    }
}

package refactoring_guru.observer.example.listeners;

import java.io.File;

public interface EventListener {
    void update(String eventType, File file);
}

package refactoring_guru.observer.example.listeners;

import java.io.File;

public class EmailNotificationListener implements EventListener {
    private String email;

    public EmailNotificationListener(String email) {
        this.email = email;
    }

    @Override
    public void update(String eventType, File file) {
        System.out.println("Email to " + email + ": Someone has performed " + eventType + " operation with the following file: " + file.getName());
    }
}

package refactoring_guru.observer.example.listeners;

import java.io.File;

public class LogOpenListener implements EventListener {
    private File log;

    public LogOpenListener(String fileName) {
        this.log = new File(fileName);
    }

    @Override
    public void update(String eventType, File file) {
        System.out.println("Save to log " + log + ": Someone has performed " + eventType + " operation with the following file: " + file.getName());
    }
}

package refactoring_guru.observer.example;

import refactoring_guru.observer.example.editor.Editor;
import refactoring_guru.observer.example.listeners.EmailNotificationListener;
import refactoring_guru.observer.example.listeners.LogOpenListener;

public class Demo {
    public static void main(String[] args) {
        Editor editor = new Editor();
        editor.events.subscribe("open", new LogOpenListener("/path/to/log/file.txt"));
        editor.events.subscribe("save", new EmailNotificationListener("admin@example.com"));

        try {
            editor.openFile("test.txt");
            editor.saveFile();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public interface Person {
  // 小王和小李通过这个接口接收小美发过来的消息
  void getMessage(String s);
}

public class LaoWang implement Person {
  pirvate String name = "小王";
  public LaoWang() {}
  
  @Overide
  public void getMessage(String s) {
    System.out.println(name + "接到了小美打过来的电话，电话内容是：" + s);
  }
}

public class LaoLi implement Person {
  private String name = "小李";
  public LaoLi() {}
  
  @Overide
  public void getMessage(String s) {
    System.out.println(name + "接到了小美打过来的电话，电话内容是：" + s);
  }
}

public class XiaoMei {
  List<Person> list = new ArrayList<Person>();
  public XiaoMel() {}
  public void addPerson(Person person) {
    list.add(person);
  }
  
  // 遍历list，把自己的通知发送给所有暗恋自己的人
  public void notifyPerson() {
    for(Person person:list) {
      person.getMessage("你们过来吧，谁先过来谁就能陪我一起玩游戏")
    }
  }
}

public static void main(String[] args){
  XiaoMei xiaomei = new XiaoMei();
  LaoWang laowang = new LaoWang();
  LaoLi laoli = new LaoLi();
  
  xiaomei.addPerson(laowang);
  xiaomei.addPerson(laoli);
  
  // 小美向小王和小李发送通知
  xiaomei.notifyPerson();
}