一、備忘錄模式介紹

1、定義與型別

定義：保存一個物件的某個狀態，以便在適當的時候恢復物件，
“后悔藥"
型別：行為型

2、適用場景

保存及恢復資料相關業務場景
后悔的時候，即想恢復到之前的狀態

3、優點

為用戶提供一種可恢復機制
存檔資訊的封裝

4、缺點

資源占用

5、相關設計模式

備忘錄模式和狀態模式

二、代碼示例

模擬場景：在網站上發布手記，暫存手記的不同版本

手記類：

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 + '\'' +
                '}';
    }
}

存檔類：

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 + '\'' +
                '}';
    }
}

存檔管理類：

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);
    }
}

測驗類：

public class Test {

    public static void main(String[] args) {
        ArticleMementorManager articleMementorManager = new ArticleMementorManager();

        Article article = new Article("如影隨形的手記A", "內容A", "圖片A");

        ArticleMemento articleMemento = article.saveToMemento();
        articleMementorManager.addMemento(articleMemento);

        System.out.println("標題：" + article.getTitle() + ",內容：" + article.getContent() + ",圖片：" + article.getImgs());
        System.out.println("完整筆記資訊：" + article);

        System.out.println("-分割線------------------------------------");

        System.out.println("修改手記start");
        article.setTitle("如影隨形的手記B");
        article.setContent("內容B");
        article.setImgs("圖片B");
        System.out.println("修改手記end");

        articleMemento = article.saveToMemento();
        articleMementorManager.addMemento(articleMemento);

        System.out.println("標題：" + article.getTitle() + ",內容：" + article.getContent() + ",圖片：" + article.getImgs());
        System.out.println("完整筆記資訊：" + article);

        System.out.println("-分割線------------------------------------");

        article.setTitle("如影隨形的手記C");
        article.setContent("內容C");
        article.setImgs("圖片C");

        System.out.println("暫存回退start");

        System.out.println("回退出堆疊1次");
        articleMemento = articleMementorManager.getMemento();
        article.undoFromMemento(articleMemento);

        System.out.println("完整筆記資訊：" + article);

        System.out.println("回退出堆疊2次");
        articleMemento = articleMementorManager.getMemento();
        article.undoFromMemento(articleMemento);

        System.out.println("暫存回退end");
        System.out.println("完整筆記資訊：" + article);
    }

}

輸出：
標題：如影隨形的手記A,內容：內容A,圖片：圖片A
完整筆記資訊：Article{title='如影隨形的手記A', content='內容A', imgs='圖片A'}
-分割線------------------------------------
修改手記start
修改手記end
標題：如影隨形的手記B,內容：內容B,圖片：圖片B
完整筆記資訊：Article{title='如影隨形的手記B', content='內容B', imgs='圖片B'}
-分割線------------------------------------
暫存回退start
回退出堆疊1次
完整筆記資訊：Article{title='如影隨形的手記B', content='內容B', imgs='圖片B'}
回退出堆疊2次
暫存回退end
完整筆記資訊：Article{title='如影隨形的手記A', content='內容A', imgs='圖片A'}

三、原始碼示例

1、spring中的webflow

標籤：設計模式

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