备忘录模式

定义

在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可将该对象恢复到原先保存的状态。

代码

需要被恢复状态类

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public class Originator {
    private String state;

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }
    //创建备忘录
    public MyMemento createMemento(){
        return new MyMemento(this.state);
    }
    //恢复备忘录
    public void restoreMemento(MyMemento memento){
        this.state = memento.getState();
    }

}

备忘录角色

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public class MyMemento {

    private String state;

    public MyMemento(String state) {
        this.state = state;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }
}

备忘录管理

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public class Caretaker {

    private MyMemento myMemento;

    public MyMemento getMyMemento() {
        return myMemento;
    }

    public void setMyMemento(MyMemento myMemento) {
        this.myMemento = myMemento;
    }
}

测试

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public class MyMementoTest {

    @Test
    public void testMemento(){
        Originator originator = new Originator();
        Caretaker caretaker = new Caretaker();
        originator.setState("before");
        System.out.println(originator.getState());
        caretaker.setMyMemento(originator.createMemento());
        originator.setState("after");
        System.out.println(originator.getState());
        originator.restoreMemento(caretaker.getMyMemento());
        System.out.println(originator.getState());
    }
}
扩展

利用clone自身备份

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public class CloneOriginator implements Cloneable{

    private CloneOriginator backUp;
    private String state;

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    //备份
    public void createMemento(){
        this.backUp = this.clone();
    }

    public void restoreMemento(){
        this.setState(this.backUp.getState());
    }

    @Override
    protected CloneOriginator clone() {
        CloneOriginator cloneOriginator;
        try {
            cloneOriginator = (CloneOriginator) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
            cloneOriginator= null;
        }
        return cloneOriginator;
    }
}

测试

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public class CloneOriginatorTest {
    @Test
    public void testCloneOriginator(){
        CloneOriginator originator = new CloneOriginator();
        originator.setState("before");
        System.out.println(originator.getState());
        originator.createMemento();
        originator.setState("after");
        System.out.println(originator.getState());
        originator.restoreMemento();
        System.out.println(originator.getState());
    }
}