【设计模式】备忘录模式 ( 简介 | 适用场景 | 优缺点 | 代码示例 )

package memento;
/**
 * 文档
 *      需要保存的对象
 */
public class Article {
    private String title;
    private String content;
    private String image;
    public Article(String tittle, String content, String image) {
        this.title = tittle;
        this.content = content;
        this.image = image;
    }
    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 getImage() {
        return image;
    }
    public void setImage(String image) {
        this.image = image;
    }
    /**
     * 保存信息到备忘录
     * @return
     */
    public ArticleMemento saveToMemento() {
        ArticleMemento articleMemento = new ArticleMemento(title, content, image);
        return articleMemento;
    }
    /**
     * 从备忘录恢复
     * @param articleMemento
     */
    public void undoFromMemento(ArticleMemento articleMemento) {
        this.title = articleMemento.getTitle();
        this.content = articleMemento.getContent();
        this.image = articleMemento.getImage();
    }
    @Override
    public String toString() {
        return "Article{" +
                "title='" + title + '\'' +
                ", content='" + content + '\'' +
                ", image='" + image + '\'' +
                '}';
    }
}

package memento;
/**
 * 文档的备忘录类
 *      主要用于存储文档的各种属性状态信息
 *  备忘录 快照 没有 set 方法
 *      只能通过构造函数设置备忘录数据
 */
public class ArticleMemento {
    private String title;
    private String content;
    private String image;
    public ArticleMemento(String title, String content, String image) {
        this.title = title;
        this.content = content;
        this.image = image;
    }
    public String getTitle() {
        return title;
    }
    public String getContent() {
        return content;
    }
    public String getImage() {
        return image;
    }
    @Override
    public String toString() {
        return "ArticleMemento{" +
                "title='" + title + '\'' +
                ", content='" + content + '\'' +
                ", image='" + image + '\'' +
                '}';
    }
}

package memento;
import java.util.Stack;
/**
 * 备忘录管理类
 */
public class ArticleMementoManager {
    /**
     * 存储所有的备忘录信息
     *      在 栈 数据结构中存储 , 特点后进先出
     */
    private final Stack<ArticleMemento> mArticleMementoStack = new Stack<>();
    /**
     * 获取栈顶的备忘录信息
     * @return
     */
    public ArticleMemento getArticleMemento() {
        return mArticleMementoStack.pop();
    }
    /**
     * 备忘录信息入栈
     *      放在栈顶
     * @param articleMemento
     */
    public void setArticleMemento(ArticleMemento articleMemento) {
        mArticleMementoStack.push(articleMemento);
    }
}

package memento;
public class Main {
    public static void main(String[] args) {
        ArticleMementoManager articleMementoManager = new ArticleMementoManager();
        // 创建并输入文档内容
        Article article = new Article("标题", "内容", "图片链接");
        // 保存备忘录信息
        ArticleMemento articleMemento = article.saveToMemento();
        // 将备忘录信息设置到 备忘录管理者
        articleMementoManager.setArticleMemento(articleMemento);
        // 打印备忘录内容
        System.out.println("文档信息 : " + article.toString());
        // 修改文档内容
        article.setTitle("标题 2");
        article.setContent("内容 2");
        article.setImage("图片链接 2");
        // 保存新的备忘录信息
        articleMemento = article.saveToMemento();
        // 将备忘录信息设置到 备忘录管理者
        articleMementoManager.setArticleMemento(articleMemento);
        // 打印备忘录内容
        System.out.println("文档信息 : " + article.toString());
        // 此时 ArticleMementoManager 中存储了 2 个存档
        // 存档 1 : Article{title='标题', content='内容', image='图片链接'}
        // 存档 2 : Article{title='标题 2', content='内容 2', image='图片链接 2'}
        // 使用备忘录回退
        // 先将栈顶的当前备忘录出栈 , 移除
        articleMementoManager.getArticleMemento();
        // 然后获取上一个备忘录 , 并设置到 Article 中
        article.undoFromMemento(articleMementoManager.getArticleMemento());
        // 打印备忘录内容
        System.out.println("文档信息 : " + article.toString());
    }
}