备忘录模式

一、备忘录模式介绍

1、定义与类型

定义：保存一个对象的某个状态，以便在适当的时候恢复对象。
"后悔药"
类型：行为型

2、适用场景

保存及恢复数据相关业务场景
后悔的时候，即想恢复到之前的状态

3、优点

为用户提供一种可恢复机制
存档信息的封装

4、缺点

资源占用

5、相关设计模式

备忘录模式和状态模式

二、代码示例

模拟场景：在网站上发布手记，暂存手记的不同版本

手记类：

public class Article { private String title; private String content; private String imgs; public String getTitle() {  return title; } public void setTitle(String title) {  this.title = title; } public String getContent() {  return content; } public void setContent(String content) {  this.content = content; } public String getImgs() {  return imgs; } public void setImgs(String imgs) {  this.imgs = imgs; } public Article(String title, String content, String imgs) {  this.title = title;  this.content = content;  this.imgs = imgs; } public ArticleMemento saveToMemento(){  ArticleMemento articleMemento = new ArticleMemento(this);  return articleMemento; } public void undoFromMemento(ArticleMemento articleMemento){  this.title = articleMemento.getTitle();  this.content = articleMemento.getContent();  this.imgs = articleMemento.getImgs(); } @Override public String toString() {  return "Article{" +    "title='" + title + '\'' +    ", content='" + content + '\'' +    ", imgs='" + imgs + '\'' +    '}'; }}

存档类：

public class ArticleMemento { private String title; private String content; private String imgs; public ArticleMemento(Article article) {  this.title = article.getTitle();  this.content = article.getContent();  this.imgs = article.getImgs(); } public ArticleMemento(String title, String content, String imgs) {  this.title = title;  this.content = content;  this.imgs = imgs; } public String getTitle() {  return title; } public String getContent() {  return content; } public String getImgs() {  return imgs; } @Override public String toString() {  return "ArticleMemento{" +    "title='" + title + '\'' +    ", content='" + content + '\'' +    ", imgs='" + imgs + '\'' +    '}'; }}

存档管理类：

public class ArticleMementorManager { private final Stack<ArticleMemento> ARTICLE_MEMENTO_STACK = new Stack<ArticleMemento>(); public ArticleMemento getMemento(){  ArticleMemento articleMemento = ARTICLE_MEMENTO_STACK.pop();  return articleMemento; } public void addMemento(ArticleMemento articleMemento){  ARTICLE_MEMENTO_STACK.push(articleMemento); }}

测试类：

public class Test { public static void main(String[] args) {  ArticleMementorManager articleMementorManager = new ArticleMementorManager();  Article article = new Article("如影随形的手记A", "内容A", "图片A");  ArticleMemento articleMemento = article.saveToMemento();  articleMementorManager.addMemento(articleMemento);  System.out.println("标题：" + article.getTitle() + ",内容：" + article.getContent() + ",图片：" + article.getImgs());  System.out.println("完整笔记信息：" + article);  System.out.println("-分割线------------------------------------");  System.out.println("修改手记start");  article.setTitle("如影随形的手记B");  article.setContent("内容B");  article.setImgs("图片B");  System.out.println("修改手记end");  articleMemento = article.saveToMemento();  articleMementorManager.addMemento(articleMemento);  System.out.println("标题：" + article.getTitle() + ",内容：" + article.getContent() + ",图片：" + article.getImgs());  System.out.println("完整笔记信息：" + article);  System.out.println("-分割线------------------------------------");  article.setTitle("如影随形的手记C");  article.setContent("内容C");  article.setImgs("图片C");  System.out.println("暂存回退start");  System.out.println("回退出栈1次");  articleMemento = articleMementorManager.getMemento();  article.undoFromMemento(articleMemento);  System.out.println("完整笔记信息：" + article);  System.out.println("回退出栈2次");  articleMemento = articleMementorManager.getMemento();  article.undoFromMemento(articleMemento);  System.out.println("暂存回退end");  System.out.println("完整笔记信息：" + article); }}

输出：
标题：如影随形的手记A,内容：内容A,图片：图片A
完整笔记信息：Article{title='如影随形的手记A', content='内容A', imgs='图片A'}
-分割线------------------------------------
修改手记start
修改手记end
标题：如影随形的手记B,内容：内容B,图片：图片B
完整笔记信息：Article{title='如影随形的手记B', content='内容B', imgs='图片B'}
-分割线------------------------------------
暂存回退start
回退出栈1次
完整笔记信息：Article{title='如影随形的手记B', content='内容B', imgs='图片B'}
回退出栈2次
暂存回退end
完整笔记信息：Article{title='如影随形的手记A', content='内容A', imgs='图片A'}

三、源码示例

1、spring中的webflow

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