备忘录模式

备忘录模式（Memento Pattern）保存一个对象的某个状态，以便在适当的时候恢复对象

备忘录模式的结构

• 发起人：记录当前时刻的内部状态，负责定义哪些属于备份范围的状态，负责创建和恢复备忘录数据。
• 备忘录：负责存储发起人对象的内部状态，在需要的时候提供发起人需要的内部状态。
• 管理角色：对备忘录进行管理，保存和提供备忘录。

Original 

package design.pattern.menento;

public class Original {
    private State state;
    private Menento menento;
    
    public Original(Storage sto) {
        state = new State();
        menento = new Menento(sto);
    }
    
    public String getState() {
        return state.getInfo();
    }
    
    public void setState(String msg) {
        state.setInfo(msg);
    }
    
    public void load() {
        menento.load();
    }
    
    public void store() {
        menento.store();
    }
    
    private class Menento {
        private Storage storage;
        private Menento(Storage storage) {
            this.storage = storage;
        }
        private void load() {
            state = storage.load();
        }
        private void store() {
            storage.store((State)state.clone());
        }
    }
}

State

package design.pattern.menento;

public class State implements Cloneable{
    private String info;
    
    {
        info = "init";
    }
    
    public void setInfo(String msg) {
        info += " -> " + msg;
    }
    public String getInfo() {
        return info;
    }
    
    @Override
    public Object clone() {
        State obj;
        try {
            obj = (State) super.clone();
            obj.info = new String(info);
            return obj;
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
            throw new RuntimeException();
        }
    }
}

Storage

package design.pattern.menento;

import java.util.ArrayList;
import java.util.List;

public class Storage {
    private List<State> list = new ArrayList<>();
    
    public State load() {
        if (list.isEmpty())
            throw new RuntimeException();
        return list.remove(0);
    }
    
    public void store(State state) {
        list.add(state);
    }
}

Client

package design.pattern.menento;

public class Client {
    public static void main(String[] args) {
        Original ori = new Original(new Storage());
        System.out.println(ori.getState());
        ori.store();
        ori.setState("change");
        System.out.println(ori.getState());
        ori.load();
        System.out.println(ori.getState());
    }
}