Quel est le pattern correspondant au code suivant ?

abstract class Logger {

    protected int level;

    protected Logger next;

    public static final int ERR = 0;

    public static final int NOTICE = 1;

    public static final int DEBUG = 2;

    public Logger setNext(Logger next) {

        this.next = next;

        return this.next;

    }

    public void message(String msg, int priority) {

        if (priority <= this.level)

            writeMessage(msg);

        else if (this.next != null)

            this.next.message(msg, priority);

    }

    public abstract void writeMessage(String msg);

}

class DebugLogger extends Logger {

    public DebugLogger(int level) {

        this.level = level;

        this.next = null;

    }

    public void writeMessage(String msg) {

        System.out.println("Debug message: " + msg);

    }

}

class EmailLogger extends Logger {

    public EmailLogger(int level) {

        this.level = level;

        this.next = null;

    }

    public void writeMessage(String msg) {

        System.out.println("Email notification: " + msg);

    }

}

class ErrorLogger extends Logger {

    public ErrorLogger(int level) {

        this.level = level;

        this.next = null;

    }

    public void writeMessage(String msg) {

        System.err.println("Error: " + msg);

    }

}

public class Main {

    public static void main(String[] args) {

        ErrorLogger logger = new ErrorLogger(Logger.ERR);

        EmailLogger logger2 = new EmailLogger(Logger.NOTICE);

        DebugLogger logger3 = new DebugLogger(Logger.DEBUG);

        logger.setNext(logger2);

        logger2.setNext(logger3);

        logger.message("An error has occurred.", Logger.ERR);

        logger.message("Step1 completed.", Logger.NOTICE);

        logger.message("Entering function y.", Logger.DEBUG);

    }

}