设计模式19-备忘录模式

1. 概念

 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。这样就可以将该对象恢复到原先保存的状态

• 发起人：记录当前时刻的内部状态，负责定义哪些属于备份范围的状态，负责创建和恢复备忘录数据。
• 备忘录：负责存储发起人对象的内部状态，在需要的时候提供发起人需要的内部状态。
• 管理角色：对备忘录进行管理，保存和提供备忘录。

2. 案例

class Originator {  
    private String state = "";  
      
    public String getState() {  
        return state;  
    }  
    public void setState(String state) {  
        this.state = state;  
    }  
    public Memento createMemento(){  
        return new Memento(this.state);  
    }  
    public void restoreMemento(Memento memento){  
        this.setState(memento.getState());  
    }  
}  
  
class Memento {  
    private String state = "";  
    public Memento(String state){  
        this.state = state;  
    }  
    public String getState() {  
        return state;  
    }  
    public void setState(String state) {  
        this.state = state;  
    }  
}  
class Caretaker {  
    private Memento memento;  
    public Memento getMemento(){  
        return memento;  
    }  
    public void setMemento(Memento memento){  
        this.memento = memento;  
    }  
}  
public class Client {  
    public static void main(String[] args){  
        Originator originator = new Originator();  
        originator.setState("状态1");  
        System.out.println("初始状态:"+originator.getState());  
        Caretaker caretaker = new Caretaker();  
        caretaker.setMemento(originator.createMemento());  
        originator.setState("状态2");  
        System.out.println("改变后状态:"+originator.getState());  
        originator.restoreMemento(caretaker.getMemento());  
        System.out.println("恢复后状态:"+originator.getState());  
    }  
}  

多状态多备份备忘录

class Originator {  
    private String state1 = "";  
    private String state2 = "";  
    private String state3 = "";  
  
    public String getState1() {  
        return state1;  
    }  
    public void setState1(String state1) {  
        this.state1 = state1;  
    }  
    public String getState2() {  
        return state2;  
    }  
    public void setState2(String state2) {  
        this.state2 = state2;  
    }  
    public String getState3() {  
        return state3;  
    }  
    public void setState3(String state3) {  
        this.state3 = state3;  
    }  
    public Memento createMemento(){  
        return new Memento(BeanUtils.backupProp(this));  
    }  
      
    public void restoreMemento(Memento memento){  
        BeanUtils.restoreProp(this, memento.getStateMap());  
    }  
    public String toString(){  
        return "state1="+state1+"state2="+state2+"state3="+state3;  
    }  
}  
class Memento {  
    private Map<String, Object> stateMap;  
      
    public Memento(Map<String, Object> map){  
        this.stateMap = map;  
    }  
  
    public Map<String, Object> getStateMap() {  
        return stateMap;  
    }  
  
    public void setStateMap(Map<String, Object> stateMap) {  
        this.stateMap = stateMap;  
    }  
}  
class BeanUtils {  
    public static Map<String, Object> backupProp(Object bean){  
        Map<String, Object> result = new HashMap<String, Object>();  
        try{  
            BeanInfo beanInfo = Introspector.getBeanInfo(bean.getClass());  
            PropertyDescriptor[] descriptors = beanInfo.getPropertyDescriptors();  
            for(PropertyDescriptor des: descriptors){  
                String fieldName = des.getName();  
                Method getter = des.getReadMethod();  
                Object fieldValue = getter.invoke(bean, new Object[]{});  
                if(!fieldName.equalsIgnoreCase("class")){  
                    result.put(fieldName, fieldValue);  
                }  
            }  
              
        }catch(Exception e){  
            e.printStackTrace();  
        }  
        return result;  
    }  
      
    public static void restoreProp(Object bean, Map<String, Object> propMap){  
        try {  
            BeanInfo beanInfo = Introspector.getBeanInfo(bean.getClass());  
            PropertyDescriptor[] descriptors = beanInfo.getPropertyDescriptors();  
            for(PropertyDescriptor des: descriptors){  
                String fieldName = des.getName();  
                if(propMap.containsKey(fieldName)){  
                    Method setter = des.getWriteMethod();  
                    setter.invoke(bean, new Object[]{propMap.get(fieldName)});  
                }  
            }  
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
    }  
}  
class Caretaker {  
    private Map<String, Memento> memMap = new HashMap<String, Memento>();  
    public Memento getMemento(String index){  
        return memMap.get(index);  
    }  
      
    public void setMemento(String index, Memento memento){  
        this.memMap.put(index, memento);  
    }  
}  
class Client {  
    public static void main(String[] args){  
        Originator ori = new Originator();  
        Caretaker caretaker = new Caretaker();  
        ori.setState1("1");  
        ori.setState2("2");  
        ori.setState3("3");  
        System.out.println("===init status===
"+ori);  
          
        caretaker.setMemento("001",ori.createMemento());  
        ori.setState1("4");  
        ori.setState2("5");  
        ori.setState3("6");  
        System.out.println("=== update status===
"+ori);  
          
        ori.restoreMemento(caretaker.getMemento("001"));  
        System.out.println("===restore status===
"+ori);  
    }  
}