备忘录模式

用一个栈保存一个对象的一系列历史状态，在需要的时候可以恢复对象

• 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，即“后悔药”
• 类型：行为型
• 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
• 优点：
  • 为用户提供一种可恢复机制
  • 存档信息的封装
• 缺点：资源占用
• 相关设计模式：
  • 备忘录模式和状态模式：备忘录模式中，是用实例来表示状态的，也就是说存档的对象是一个实例对象，而在状态模式中是类表示状态

Coding

/**
 * 文章类
 */
public class Article {

    private String title;
    private String content;
    private String imgs;

    public Article(String title, String content, String imgs) {
        this.title = title;
        this.content = content;
        this.imgs = 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 ArticleMemento saveToMemento() {
        ArticleMemento articleMemento = new ArticleMemento(this.title, this.content, this.imgs);
        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 + '\'' +
                '}';
    }
}
/**
 * 文章快照
 */
public class ArticleMemento {
    private String title;
    private String content;
    private String imgs;

    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 + '\'' +
                '}';
    }
}
/**
 * 文章快照管理者
 */
public class ArticleMementoManager {

    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);
    }

}

 

 

UML

测试类

public class Test {

    public static void main(String[] args) {
        ArticleMementoManager articleMementoManager = new ArticleMementoManager();

        Article article= new Article("如影随行的设计模式A","手记内容A","手记图片A");

        ArticleMemento articleMemento = article.saveToMemento();

        articleMementoManager.addMemento(articleMemento);
        System.out.println("标题:"+article.getTitle()+" 内容:"+article.getContent()+" 图片:"+article.getImgs()+" 暂存成功");

        System.out.println("手记完整信息:"+article);

        System.out.println("修改手记start");

        article.setTitle("如影随行的设计模式B");
        article.setContent("手记内容B");
        article.setImgs("手记图片B");

        System.out.println("修改手记end");

        System.out.println("手记完整信息:"+article);

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

        article.setTitle("如影随行的设计模式C");
        article.setContent("手记内容C");
        article.setImgs("手记图片C");

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

        System.out.println("回退出栈1次");
        articleMemento = articleMementoManager.getMemento();
        article.undoFromMemento(articleMemento);

        System.out.println("回退出栈2次");
        articleMemento = articleMementoManager.getMemento();
        article.undoFromMemento(articleMemento);

        System.out.println("暂存回退end");
        System.out.println("手记完整信息:"+article);

    }
}
==========输出===========
标题:如影随行的设计模式A 内容:手记内容A 图片:手记图片A 暂存成功
手记完整信息:Article{title='如影随行的设计模式A', content='手记内容A', imgs='手记图片A'}
修改手记start
修改手记end
手记完整信息:Article{title='如影随行的设计模式B', content='手记内容B', imgs='手记图片B'}
暂存回退start
回退出栈1次
回退出栈2次
暂存回退end
手记完整信息:Article{title='如影随行的设计模式A', content='手记内容A', imgs='手记图片A'}