Memento概述

Memento - 图1

UML概述

Memento - 图2

玩具代码案例1 - 模拟浏览器的回退&前进操作

备忘录发起者

Browser

  1. package online.javabook.gof.behavioral.patterns5.memento1.browser.context;
  3. import online.javabook.gof.behavioral.patterns5.memento1.browser.memento.History;
  4. import online.javabook.gof.behavioral.patterns5.memento1.browser.memento.Memento;
  6. public class Browser {
  8.     private History history = new History();
  10.     private String url;
  12.     public void go(String url) {
  13.         this.url = url;
  14.         history.add(new Memento(url));
  15.         System.out.println("->" + url);
  16.     }
  18.     public void back() {
  19.         Memento memento = history.getUndo();
  20.         this.url = memento.getState();
  21.         System.out.println("<-" + url);
  22.     }
  24.     public void forward() {
  25.         Memento memento = history.getRedo();
  26.         this.url = memento.getState();
  27.         System.out.println("->" + url);
  28.     }
  30. }

备忘录回放

History

  1. package online.javabook.gof.behavioral.patterns5.memento1.browser.memento;
  3. import java.util.ArrayList;
  4. import java.util.List;
  6. public class History {
  8.     private int index = -1;
  10.     private List<Memento> mementoList = new ArrayList<Memento>();
  12.     public void add(Memento state){
  13.         mementoList.add(state);
  14.         index++;
  15.     }
  17.     public Memento get(int index){
  18.         return mementoList.get(index);
  19.     }
  21.     public Memento getUndo() {
  22.         if (index == -1) {
  23.             return null;
  24.         }
  25.         index = Math.max(0, --index);
  26.         return mementoList.get(index);
  27.     }
  29.     public Memento getRedo() {
  30.         if (index == mementoList.size()) {
  31.             return null;
  32.         }
  33.         index = Math.min(mementoList.size() - 1, ++index);
  34.         return mementoList.get(index);
  35.     }
  36. }

备忘录状态

Memento

  1. package online.javabook.gof.behavioral.patterns5.memento1.browser.memento;
  3. public class Memento {
  5.     private String url;
  7.     public Memento(String url){
  8.         this.url = url;
  9.     }
  11.     public String getState(){
  12.         return url;
  13.     }
  14. }

备忘录测试

Main

  1. package online.javabook.gof.behavioral.patterns5.memento1.browser.app;
  3. import online.javabook.gof.behavioral.patterns5.memento1.browser.context.Browser;
  5. public class Main {
  6.     public static void main(String[] args) {
  7.         Browser browser = new Browser();
  8.         browser.go("http://www.1.com");
  9.         browser.go("http://www.2.com");
  10.         browser.go("http://www.3.com");
  11.         browser.go("http://www.4.com");
  12.         browser.go("http://www.5.com");
  13.         browser.go("http://www.6.com");
  15.         browser.back();
  16.         browser.back();
  17.         browser.back();
  18.         browser.back();
  19.         browser.back();
  20.         browser.back();
  21.         browser.back();
  23.         browser.forward();
  24.         browser.forward();
  25.         browser.forward();
  26.         browser.forward();
  27.         browser.forward();
  28.         browser.forward();
  29.         browser.forward();
  31.         browser.back();
  32.         browser.back();
  33.         browser.back();
  35.     }
  36. }

Console

  1. ->http://www.1.com
  2. ->http://www.2.com
  3. ->http://www.3.com
  4. ->http://www.4.com
  5. ->http://www.5.com
  6. ->http://www.6.com
  7. <-http://www.5.com
  8. <-http://www.4.com
  9. <-http://www.3.com
  10. <-http://www.2.com
  11. <-http://www.1.com
  12. <-http://www.1.com
  13. <-http://www.1.com
  14. ->http://www.2.com
  15. ->http://www.3.com
  16. ->http://www.4.com
  17. ->http://www.5.com
  18. ->http://www.6.com
  19. ->http://www.6.com
  20. ->http://www.6.com
  21. <-http://www.5.com
  22. <-http://www.4.com
  23. <-http://www.3.com

玩具代码案例2 - 图形编辑器与备忘录模式

图形编辑器中的redo/undo可能是备忘录模式的源头，这个案例中我们结合了命令模式（命令即状态）和备忘录模式

备忘录发起者

GraphEditor

  1. package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.context;
  3. import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command.ColorCommand;
  4. import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command.IGraphCommand;
  5. import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command.MoveCommand;
  6. import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.memen.GraphCommandHistory;
  7. import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.memen.GraphCommandMemento;
  9. import java.awt.*;
  11. public class GraphEditor {
  13.     private GraphCommandHistory history = new GraphCommandHistory();
  15.     private Shape shape = new Shape();
  17.     public void color(Color newColor) {
  18.         IGraphCommand command = new ColorCommand(newColor);
  19.         command.execute(shape);
  21.         GraphCommandMemento memento = new GraphCommandMemento(command);
  22.         history.add(memento);
  24.         System.out.println("->" + shape);
  25.     }
  27.     public void move(Point newPoint) {
  28.         IGraphCommand command = new MoveCommand(newPoint);
  29.         command.execute(shape);
  31.         GraphCommandMemento memento = new GraphCommandMemento(command);
  32.         history.add(memento);
  34.         System.out.println("->" + shape);
  35.     }
  37.     public void undo() {
  38.         GraphCommandMemento memento = history.getUndo();
  39.         IGraphCommand command = memento.getState();
  40.         command.execute(shape);
  42.         System.out.println("<-" + shape);
  43.     }
  45.     public void redo() {
  46.         GraphCommandMemento memento = history.getRedo();
  47.         IGraphCommand command = memento.getState();
  48.         command.execute(shape);
  50.         System.out.println("->" + shape);
  51.     }
  52. }

备忘录回放

History

  1. package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.memen;
  3. import java.util.ArrayList;
  4. import java.util.List;
  6. public class GraphCommandHistory {
  8.     private int index = -1;
  10.     private List<GraphCommandMemento> mementoList = new ArrayList<GraphCommandMemento>();
  12.     public void add(GraphCommandMemento state){
  13.         mementoList.add(state);
  14.         index++;
  15.     }
  17.     public GraphCommandMemento get(int index){
  18.         return mementoList.get(index);
  19.     }
  21.     public GraphCommandMemento getUndo() {
  22.         if (index == -1) {
  23.             return null;
  24.         }
  25.         index = Math.max(0, --index);
  26.         return mementoList.get(index);
  27.     }
  29.     public GraphCommandMemento getRedo() {
  30.         if (index == mementoList.size()) {
  31.             return null;
  32.         }
  33.         index = Math.min(mementoList.size() - 1, ++index);
  34.         return mementoList.get(index);
  35.     }
  36. }

备忘录状态

Memento

  1. package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.memen;
  3. import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command.IGraphCommand;
  5. public class GraphCommandMemento {
  7.     private IGraphCommand graphCommand;
  9.     public GraphCommandMemento(IGraphCommand graphCommand){
  10.         this.graphCommand = graphCommand;
  11.     }
  13.     public IGraphCommand getState(){
  14.         return graphCommand;
  15.     }
  16. }

备忘录命令

IGraphCommand

package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command;

import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.context.Shape;

public interface IGraphCommand {
    void execute(Shape shape);
}

ColorCommand

package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command;

import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.context.Shape;

import java.awt.*;

public class ColorCommand implements IGraphCommand {

    private Color color;

    public ColorCommand(Color newColor) {
        this.color = newColor;
    }

    @Override
    public void execute(Shape shape) {
        shape.setColor(color);
    }
}

MoveCommand

package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.command;

import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.context.Shape;

import java.awt.*;

public class MoveCommand implements IGraphCommand {

    private Point point;

    public MoveCommand(Point newPoint) {
        this.point = newPoint;
    }

    @Override
    public void execute(Shape shape) {
        shape.setPoint(point);
    }
}

备忘录测试

Main

package online.javabook.gof.behavioral.patterns5.memento2.grapheditor.app;

import online.javabook.gof.behavioral.patterns5.memento2.grapheditor.context.GraphEditor;

import java.awt.*;

public class Main {
    public static void main(String[] args) {
        GraphEditor graphEditor = new GraphEditor();
        graphEditor.color(Color.red);
        graphEditor.color(Color.orange);
        graphEditor.color(Color.yellow);

        graphEditor.move(new Point(1,1));
        graphEditor.move(new Point(2,2));
        graphEditor.move(new Point(3,3));

        graphEditor.undo();
        graphEditor.undo();

        graphEditor.redo();
        graphEditor.redo();
    }
}

Console

->Shape{color=java.awt.Color[r=255,g=0,b=0], point=java.awt.Point[x=0,y=0]}
->Shape{color=java.awt.Color[r=255,g=200,b=0], point=java.awt.Point[x=0,y=0]}
->Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=0,y=0]}
->Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=1,y=1]}
->Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=2,y=2]}
->Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=3,y=3]}
<-Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=2,y=2]}
<-Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=1,y=1]}
->Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=2,y=2]}
->Shape{color=java.awt.Color[r=255,g=255,b=0], point=java.awt.Point[x=3,y=3]}