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editor
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editor/Editor.java
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."); } } }
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listeners
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listeners/EmailNotificationListener.java
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()); } }
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listeners/EventListener.java
package refactoring_guru.observer.example.listeners; import java.io.File; public interface EventListener { void update(String eventType, File file); }
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listeners/LogOpenListener.java
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()); } }
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publisher
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publisher/EventManager.java
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); } } }
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Demo.java
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();
}
}
}
Save to log \path\to\log\file.txt: Someone has performed open operation with the following file: test.txt
Email to admin@example.com: Someone has performed save operation with the following file: test.txt