设计模式——备忘录模式（Memo Pattern）

定义：备忘录模式又称为快照模式（Snapshot Pattern），在不破坏封装的前提下，捕获一个对象的内部状态，并将状态保存在对象之外，这样以后就可以将此对象恢复到初始保存的状态，类似于“后悔药”。属于行为型模式。

适用场景：

1）需要保存历史快照的场景；
2）希望在对象之外保存状态，且其他对象无法访问状态保存的具体内容；

角色：发起人，备忘录，备忘录管理者

代码演示

备忘录类

package com.lucifer.designpattern.memo;

import java.util.Date;

public class ArticleMemo {
    private String title;
    private String content;
    private Date createTime;

    public ArticleMemo(String title, String content, Date createTime) {
        this.title = title;
        this.content = content;
        this.createTime = createTime;
    }

    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 Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }

    @Override
    public String toString() {
        return "ArticleMemo{" +
                "title='" + title + ''' +
                ", content='" + content + ''' +
                ", createTime=" + createTime +
                '}';
    }
}

编辑器类

package com.lucifer.designpattern.memo;

import java.util.Date;

public class Editor {
    private String title;
    private String content;
    private Date createTime;
    private DraftBox draftBox = DraftBox.getInstance();

    public Editor(String title, String content, Date createTime) {
        this.title = title;
        this.content = content;
        this.createTime = createTime;
    }

    public void saveToMemo() {
        ArticleMemo memo = new ArticleMemo(this.title, this.content, this.createTime);
        draftBox.addMemo(memo);
    }

    public void undoFromMemo() {
        ArticleMemo memo = draftBox.getMemo();
        this.title = memo.getTitle();
        this.content = memo.getContent();
        this.createTime = memo.getCreateTime();
    }

    @Override
    public String toString() {
        return "Editor{" +
                "title='" + title + ''' +
                ", content='" + content + ''' +
                ", createTime=" + createTime +
                '}';
    }
}

草稿箱类

package com.lucifer.designpattern.memo;

import java.util.Stack;

public class DraftBox {
    private static DraftBox draftBox = new DraftBox();
    private final Stack STACK = new Stack();
    private DraftBox() {}
    public static DraftBox getInstance() {
        return draftBox;
    }
    public ArticleMemo getMemo() {
        ArticleMemo memo = STACK.pop();
        return  memo;
    }
    public void addMemo(ArticleMemo memo) {
        STACK.push(memo);
    }
}

测试类

package com.lucifer.designpattern.memo;

import java.util.Date;

public class MemoTest {
    public static void main(String[] args) {
        Editor editor = new Editor("备忘录模式", "备忘录模式又称为快照模式（Snapshot Pattern）", new Date());
        editor.saveToMemo();
        System.out.println("第一次保存到草稿箱：" + editor.toString());

        editor = new Editor("备忘录模式", "备忘录模式又称为快照模式（Snapshot Pattern），在不破坏封装的前提下，捕获一个对象的内部状态，并将状态保存在对象之外，这样以后就可以将此对象恢复到初始保存的状态，类似于“后悔药”。属于行为型模式。", new Date());
        editor.saveToMemo();
        System.out.println("第二次保存到草稿箱：" + editor.toString());

        editor.undoFromMemo();
        System.out.println("第一次撤回内容：" + editor.toString());

        editor.undoFromMemo();
        System.out.println("第二次撤回内容：" + editor.toString());

    }
}

执行结果