設計模式之備忘錄模式

王若伊_恩赐解脱發表於2024-09-02
設計模式

備忘錄模式（Memento Pattern）官方的定義是這樣的：
在不破壞封閉的前提下，捕獲一個物件的內部狀態，並在該物件之外儲存這個狀態。這樣以後就可將該物件恢復到原先儲存的狀態。它是物件導向的23種設計模式中的一種，屬於行為模式的範圍。
直白點說就是：
我們可以在不暴露更多欄位的前提下，直接將某個物件儲存到其他地方，可以是磁碟，也可以是記憶體。
有些地方也將之稱為快照模式，就是給當前物件做一個快照。

一般我們將備忘錄模式定義為3個組成角色：
1、Originator 發起人，有些人將他翻譯為原發器，我是非常不認同的。
什麼叫原發器？本人查了辭海等線上網站，壓根就沒有這個詞，我非常不人認同最初的譯者，憑感覺隨意造詞。
Originator 查詢了谷歌翻譯(防盜連線：本文首發自http://www.cnblogs.com/jilodream/ )
a person who creates or initiates something.
大概可以理解為 創始人或者是最初發起某個事情的人，所以這裡可以理解為驅動、發起生成備忘錄的角色。
2、Memento 備忘錄，用來儲存要儲存物件的內部狀態，也就是快照。
3、Caretaker 負責人 負責儲存和管理備忘錄的。

下面我們寫一個例子，
背景：模仿超級馬里奧，可以吃金幣，移動

主類：

 1 package com.example.demo.learn.pattern.behavior.memento;
 2 
 3 import com.alibaba.nacos.shaded.com.google.common.collect.Maps;
 4 
 5 import java.util.Map;
 6 
 7 /**
 8  * @discription
 9  */
10 public class RecordSystem {
11 
12     private static Map<String, String> recordMap = Maps.newHashMap();
13 
14     public static void saveRecord(MapInfo mapInfo, String index) {
15         recordMap.put(index, mapInfo.saveRecord());
16     }
17 
18     public static MapInfo getRecord(String time) {
19         if (recordMap.containsKey(time)) {
20             return MapInfo.loadRecord(recordMap.get(time));
21         }
22         return null;
23     }
24 }

遊戲內容類：

 1 package com.example.demo.learn.pattern.behavior.memento;
 2 
 3 import com.alibaba.fastjson.JSON;
 4 import lombok.Data;
 5 
 6 /**
 7  * @discription
 8  */
 9 @Data
10 public class MapInfo {
11     private Location marioLocation = new Location(0, 100, 1);
12     private int golden = 0;
13 
14     public void touchGolden() {
15         golden++;
16     }
17 
18     public void marioMove(int xv, int yv) {
19         int newX = marioLocation.getX() + xv;
20         marioLocation.setX(newX);
21 
22         int newY = marioLocation.getY() + yv;
23         marioLocation.setY(newY);
24     }
25 
26     //馬里奧調頭
27     public void marioTuneBack() {
28         int forward = marioLocation.getForward() * -1;
29         marioLocation.setX(forward);
30     }
31 
32     public String saveRecord() {
33         return JSON.toJSONString(marioLocation) + ";" + golden;
34     }
35 
36     public static MapInfo loadRecord(String recordContent) {
37         String[] contents = recordContent.split(";");
38         MapInfo mapInfo = new MapInfo();
39         Location marioLocation = JSON.parseObject(contents[0], Location.class);
40         mapInfo.setMarioLocation(marioLocation);
41         mapInfo.setGolden(Integer.valueOf(contents[1]));
42         return mapInfo;
43     }
44 
45     public static MapInfo initMap() {
46         MapInfo mapInfo = new MapInfo();
47         return mapInfo;
48     }
49 }

package com.example.demo.learn.pattern.behavior.memento;

import lombok.AllArgsConstructor;
import lombok.Data;

/**
 * @discription
 */

@AllArgsConstructor
@Data
public class Location {
    //座標
    private int x;
    //座標
    private int y;

    //方向 -1向左，1向右
    private int forward;
}

遊戲記錄儲存

 1 package com.example.demo.learn.pattern.behavior.memento;
 2 
 3 import com.alibaba.nacos.shaded.com.google.common.collect.Maps;
 4 
 5 import java.util.Map;
 6 
 7 /**
 8  * @discription
 9  */
10 public class RecordSystem {
11 
12     private static Map<String, String> recordMap = Maps.newHashMap();
13 
14     public static void saveRecord(MapInfo mapInfo, String index) {
15         recordMap.put(index, mapInfo.saveRecord());
16     }
17 
18     public static MapInfo getRecord(String time) {
19         if (recordMap.containsKey(time)) {
20             return MapInfo.loadRecord(recordMap.get(time));
21         }
22         return null;
23     }
24 }

輸出大概是這樣：

"C:\Program Files\Java\jdk-11\bin\java.exe" "-javaagent:E:\Program Files\JetBrains\IntelliJ IDEA 2023.2\lib\idea_rt.jar=65256:E:\Program Files\JetBrains\IntelliJ IDEA 2023.2\bin" -Dfile.encoding=UTF-8 -classpath 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com.example.demo.learn.pattern.behavior.memento.PatternMain
16:10:40.045 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 存檔中。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 1號存檔已完成。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain (防盜連線：本文首發自http://www.cnblogs.com/jilodream/ )- 存檔中。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 2號存檔已完成。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 讀檔中。。。
16:10:40.192 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 1號讀檔已完成。。。

Process finished with exit code 0

在這個例子中 MapInfo 擁有了所有內部狀態屬性，但是並不直接暴露出來，我們透過它的save介面，來獲取物件的所有狀態。

這個例子中它負責發起資料的儲存，充當了Originator的角色；
而RecordSystem類，負責管理和儲存備忘錄屬於caretaker角色。
RecordSystem類中的 recordMap，負責充當備忘錄的角色，也就是儲存快照的物件；

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