DesignPattern 设计模式 - 总览

来源：RUNOOB.COM 设计模式

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1 创建型模式

这些设计模式提供了一种在创建对象的同时隐藏创建逻辑的方式，而不是使用 new 运算符直接实例化对象。这使得程序在判断针对某个给定实例需要创建哪些对象时更加灵活。

工厂模式（Factory Pattern）

ShapeFactory shapeFactory = new ShapeFactory();

// 获取 Circle 的对象，并调用它的 draw 方法 
Shape shape1 = shapeFactory.getShape("CIRCLE");

// 调用 Circle 的 draw 方法 
shape1.draw();

反射机制可以解决每次增加一个产品时，都需要增加一个对象实现工厂的缺点

抽象工厂模式（Abstract Factory Pattern）

// 获取形状工厂 
AbstractFactory shapeFactory = FactoryProducer.getFactory("SHAPE");

// 获取形状为 Circle 的对象 
Shape shape1 = shapeFactory.getShape("CIRCLE");

// 调用 Circle 的 draw 方法 
shape1.draw();

单例模式（Singleton Pattern）

// 获取唯一可用的对象 
SingleObject object = SingleObject.getInstance();

单例实现方式

• 懒汉
• 懒汉，线程安全
• 懒汉，双检锁
• 饿汉
• 静态内部类
• 枚举

  建造者模式（Builder Pattern）

public class MealBuilder {

   public Meal prepareVegMeal (){
      Meal meal = new Meal();
      meal.addItem(new VegBurger());
      meal.addItem(new Coke());
      return meal;
   }   

   public Meal prepareNonVegMeal (){
      Meal meal = new Meal();
      meal.addItem(new ChickenBurger());
      meal.addItem(new Pepsi());
      return meal;
   }
}
      
      MealBuilder mealBuilder = new MealBuilder();

      Meal vegMeal = mealBuilder.prepareVegMeal();

原型模式（Prototype Pattern）

import java.util.Hashtable;

public class ShapeCache {
    
   private static Hashtable<String, Shape> shapeMap 
      = new Hashtable<String, Shape>();

   public static Shape getShape(String shapeId) {
      Shape cachedShape = shapeMap.get(shapeId);
      return (Shape) cachedShape.clone();
   }

   // 对每种形状都运行数据库查询，并创建该形状 
   // shapeMap.put(shapeKey, shape);
   // 例如，我们要添加三种形状 
   public static void loadCache() {
      Circle circle = new Circle();
      circle.setId("1");
      shapeMap.put(circle.getId(),circle);

      Square square = new Square();
      square.setId("2");
      shapeMap.put(square.getId(),square);

      Rectangle rectangle = new Rectangle();
      rectangle.setId("3");
      shapeMap.put(rectangle.getId(),rectangle);
   }
}

      ShapeCache.loadCache();
      Shape clonedShape = (Shape) ShapeCache.getShape("1");
      System.out.println("Shape :" + clonedShape.getType());

2 结构型模式

这些设计模式关注类和对象的组合。继承的概念被用来组合接口和定义组合对象获得新功能的方式。

适配器模式（Adapter Pattern）

public class MediaAdapter implements MediaPlayer {

   AdvancedMediaPlayer advancedMusicPlayer;

   public MediaAdapter(String audioType){
      if(audioType.equalsIgnoreCase("vlc") ){
         advancedMusicPlayer = new VlcPlayer();            
      } else if (audioType.equalsIgnoreCase("mp4")){
         advancedMusicPlayer = new Mp4Player();
      }    
   }

   @Override
   public void play(String audioType, String fileName) {
      if(audioType.equalsIgnoreCase("vlc")){
         advancedMusicPlayer.playVlc(fileName);
      }else if(audioType.equalsIgnoreCase("mp4")){
         advancedMusicPlayer.playMp4(fileName);
      }
   }
}

桥接模式（Bridge Pattern）

public abstract class Shape {
   protected DrawAPI drawAPI;
   protected Shape(DrawAPI drawAPI){
      this.drawAPI = drawAPI;
   }
   public abstract void draw();    
}

过滤器模式（Filter、Criteria Pattern）

List<Person> malePersons = new ArrayList<Person>(); 
for (Person person : persons) {
   if(person.getGender().equalsIgnoreCase("MALE")){
      malePersons.add(person);
   }
}

组合模式（Composite Pattern）

Employee CEO = new Employee("John","CEO", 30000);
Employee headSales = new Employee("Robert","Head Sales", 20000);
CEO.add(headSales);

装饰器模式（Decorator Pattern）

public class RedShapeDecorator extends ShapeDecorator {

   public RedShapeDecorator(Shape decoratedShape) {
      super(decoratedShape);        
   }

   @Override
   public void draw() {
      decoratedShape.draw();           
      setRedBorder(decoratedShape);
   }

   private void setRedBorder(Shape decoratedShape){
      System.out.println("Border Color: Red");
   }
}

Shape redCircle = new RedShapeDecorator(new Circle());
redCircle.draw();

外观模式（Facade Pattern）

public class ShapeMaker {
   private Shape circle;

  public ShapeMaker() {
      circle = new Circle();
   }

   public void drawCircle(){
      circle.draw();
   }
}

ShapeMaker shapeMaker = new ShapeMaker();
shapeMaker.drawCircle();

享元模式（Flyweight Pattern）

public class ShapeFactory {
   private static final HashMap<String, Shape> circleMap = new HashMap<>();

   public static Shape getCircle(String color) {
      Circle circle = (Circle)circleMap.get(color);

      if(circle == null) {
         circle = new Circle(color);
         circleMap.put(color, circle);
         System.out.println("Creating circle of color :" + color);
      }
      return circle;
   }
}

Circle circle =  (Circle)ShapeFactory.getCircle("RED"");
circle.draw();

代理模式（Proxy Pattern）

public class ProxyImage implements Image{

   private RealImage realImage;
   private String fileName;

   public ProxyImage(String fileName){
      this.fileName = fileName;
   }

   @Override
   public void display() {
      if(realImage == null){
         realImage = new RealImage(fileName);
      }
      realImage.display();
   }
}

3 行为型模式

这些设计模式特别关注对象之间的通信。

责任链模式（Chain of Responsibility Pattern）

public abstract class AbstractLogger {
   public static int INFO = 1;
   public static int DEBUG = 2;
   public static int ERROR = 3;

   protected int level;

   // 责任链中的下一个元素 
   protected AbstractLogger nextLogger;

   public void setNextLogger(AbstractLogger nextLogger){
      this.nextLogger = nextLogger;
   }

   public void logMessage(int level, String message){
      if(this.level <= level){
         write(message);
      }
      if(nextLogger !=null){
         nextLogger.logMessage(level, message);
      }
   }

   abstract protected void write(String message);
    
}

命令模式（Command Pattern）

public class BuyStock implements Order {
   private Stock abcStock;

   public BuyStock(Stock abcStock){
      this.abcStock = abcStock;
   }

   public void execute() {
      abcStock.buy();
   }
}

解释器模式（Interpreter Pattern）

public static Expression getMaleExpression(){
   Expression robert = new TerminalExpression("Robert");
   Expression john = new TerminalExpression("John");
   return new OrExpression(robert, john);        
}

Expression isMale = getMaleExpression();
System.out.println("John is male?" + isMale.interpret("John"));

迭代器模式（Iterator Pattern）

中介者模式（Mediator Pattern）

备忘录模式（Memento Pattern）

观察者模式（Observer Pattern）

public class Subject {
    
   private List<Observer> observers 
      = new ArrayList<Observer>();
   private int state;

   public int getState() {
      return state;
   }

   public void setState(int state) {
      this.state = state;
      // 状态发生变化时，自动通知观察者 
      notifyAllObservers();
   }

   public void attach(Observer observer){
      observers.add(observer);        
   }
   
   public void notifyAllObservers(){
      for (Observer observer : observers) {
         observer.update();
      }
   }     
}

状态模式（State Pattern）

空对象模式（Null Object Pattern）

public class CustomerFactory {
    
   public static final String[] names = {"Rob", "Joe", "Julie"};

   public static AbstractCustomer getCustomer(String name){
      for (int i = 0; i < names.length; i++) {
         if (names[i].equalsIgnoreCase(name)){
            return new RealCustomer(name);
         }
      }
      return new NullCustomer();
   }
}

策略模式（Strategy Pattern）

模板模式（Template Pattern）

public abstract class Game {
   abstract void initialize();
   abstract void startPlay();
   abstract void endPlay();

   // 模板 
   public final void play(){

      // 初始化游戏 
      initialize();

      // 开始游戏 
      startPlay();

      // 结束游戏 
      endPlay();
   }
}

访问者模式（Visitor Pattern）

public class Computer implements ComputerPart {
    
   ComputerPart[] parts;

   public Computer(){
      parts = new ComputerPart[] {new Mouse(), new Keyboard(), new Monitor()};        
   } 


   @Override
   public void accept(ComputerPartVisitor computerPartVisitor) {
      for (int i = 0; i < parts.length; i++) {
         parts[i].accept(computerPartVisitor);
      }
      computerPartVisitor.visit(this);
   }
}

ComputerPart computer = new Computer();
computer.accept(new ComputerPartDisplayVisitor());

4 J2EE 模式

这些设计模式特别关注表示层。这些模式是由 Sun Java Center 鉴定的。

MVC 模式（MVC Pattern）

// 从数据可获取学生记录 
Student model  = retriveStudentFromDatabase();

// 创建一个视图：把学生详细信息输出到控制台 
StudentView view = new StudentView();

StudentController controller = new StudentController(model, view);

controller.updateView();

// 更新模型数据 
controller.setStudentName("John");

controller.updateView();

业务代表模式（Business Delegate Pattern）

public class BusinessDelegate {
   private BusinessLookUp lookupService = new BusinessLookUp();
   private BusinessService businessService;
   private String serviceType;

   public void setServiceType(String serviceType){
      this.serviceType = serviceType;
   }

   public void doTask(){
      businessService = lookupService.getBusinessService(serviceType);
      businessService.doProcessing();        
   }
}

组合实体模式（Composite Entity Pattern）

public class CoarseGrainedObject {
   DependentObject1 do1 = new DependentObject1();
   DependentObject2 do2 = new DependentObject2();

   public void setData(String data1, String data2){
      do1.setData(data1);
      do2.setData(data2);
   }

   public String[] getData(){
      return new String[] {do1.getData(),do2.getData()};
   }
}

public class CompositeEntity {
   private CoarseGrainedObject cgo = new CoarseGrainedObject();

   public void setData(String data1, String data2){
      cgo.setData(data1, data2);
   }

   public String[] getData(){
      return cgo.getData();
   }
}

数据访问对象模式（Data Access Object Pattern）

public interface StudentDao {
   public List<Student> getAllStudents();
   public Student getStudent(int rollNo);
   public void updateStudent(Student student);
   public void deleteStudent(Student student);
}

前端控制器模式（Front Controller Pattern）

public class FrontController {
    
   private Dispatcher dispatcher;

   public FrontController(){
      dispatcher = new Dispatcher();
   }

   private boolean isAuthenticUser(){
      System.out.println("User is authenticated successfully.");
      return true;
   }

   private void trackRequest(String request){
      System.out.println("Page requested:" + request);
   }

   public void dispatchRequest(String request){
      // 记录每一个请求 
      trackRequest(request);
      // 对用户进行身份验证 
      if(isAuthenticUser()){
         dispatcher.dispatch(request);
      }    
   }
}

拦截过滤器模式（Intercepting Filter Pattern）

public class FilterChain {
   private List<Filter> filters = new ArrayList<Filter>();
   private Target target;

   public void addFilter(Filter filter){
      filters.add(filter);
   }

   public void execute(String request){
      for (Filter filter : filters) {
         filter.execute(request);
      }
      target.execute(request);
   }

   public void setTarget(Target target){
      this.target = target;
   }
}

服务定位器模式（Service Locator Pattern）

public class ServiceLocator {
   private static Cache cache;

   static {
      cache = new Cache();        
   }

   public static Service getService(String jndiName){

      Service service = cache.getService(jndiName);

      if(service != null){
         return service;
      }

      InitialContext context = new InitialContext();
      Service service1 = (Service)context.lookup(jndiName);
      cache.addService(service1);
      return service1;
   }
}

传输对象模式（Transfer Object Pattern）

// 类似于 Service 层 
StudentBO studentBusinessObject = new StudentBO();

// 输出所有的学生 
for (StudentVO student : studentBusinessObject.getAllStudents()) {
   System.out.println("Student: [RollNo :"
   +student.getRollNo()+", Name :"+student.getName()+"]");
}

// 更新学生 
StudentVO student =studentBusinessObject.getAllStudents().get(0);
student.setName("Michael");
studentBusinessObject.updateStudent(student);

// 获取学生 
studentBusinessObject.getStudent(0);
System.out.println("Student: [RollNo :"
+student.getRollNo()+", Name :"+student.getName()+"]");