设计模式之备忘录模式

宿遘稠 · 2025-6-9 09:36:57

备忘录模式（Memento Pattern）官方的定义是这样的：
在不破坏封闭的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可将该对象恢复到原先保存的状态。它是面向对象的23种设计模式中的一种，属于行为模式的范围。
直白点说就是：
我们可以在不暴露更多字段的前提下，直接将某个对象保存到其他地方，可以是磁盘，也可以是内存。
有些地方也将之称为快照模式，就是给当前对象做一个快照。
一般我们将备忘录模式定义为3个组成角色：
1、Originator 发起人，有些人将他翻译为原发器，我是非常不认同的。
什么叫原发器？本人查了辞海等在线网站，压根就没有这个词，我非常不人认同最初的译者，凭感觉随意造词。
Originator 查询了谷歌翻译(防盗连接：本文首发自http://www.cnblogs.com/jilodream/ )
a person who creates or initiates something.
大概可以理解为创始人或者是最初发起某个事情的人，所以这里可以理解为驱动、发起生成备忘录的角色。
2、Memento 备忘录，用来存储要保存对象的内部状态，也就是快照。
3、Caretaker 负责人负责保存和管理备忘录的。
下面我们写一个例子，
背景：模仿超级马里奥，可以吃金币，移动
主类：

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 }

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游戏内容类：

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 //马里奥调头
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 }

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package com.example.demo.learn.pattern.behavior.memento;
import lombok.AllArgsConstructor;
import lombok.Data;
/**
* @discription
*/
@AllArgsConstructor
@Data
public class Location {
//坐标
private int x;
//坐标
private int y;
//方向 -1向左，1向右
private int forward;
}

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游戏记录存储

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 }

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输出大概是这样：

"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 - 存档中。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 1号存档已完成。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain (防盗连接：本文首发自http://www.cnblogs.com/jilodream/ )- 存档中。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 2号存档已完成。。。
16:10:40.173 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 读档中。。。
16:10:40.192 [main] WARN com.example.demo.learn.pattern.behavior.memento.PatternMain - 1号读档已完成。。。
Process finished with exit code 0

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在这个例子中 MapInfo 拥有了所有内部状态属性，但是并不直接暴露出来，我们通过它的save接口，来获取对象的所有状态。
这个例子中它负责发起数据的保存，充当了Originator的角色；
而RecordSystem类，负责管理和保存备忘录属于caretaker角色。
RecordSystem类中的 recordMap，负责充当备忘录的角色，也就是保存快照的对象；

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