模版方法（Template Method Pattern）

    Template Method:Define the skeleton of an algorithm in an operation, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm's structure.

父类定义一个算法的框架，把一些操作放在子类中去实现．子类不改变算法的大的框架，只是重新定义一些核心的步骤．

例子１：

 

一个咖啡店，卖咖啡和茶。

制作咖啡的步骤是：

1. 把水煮开。
2. 放入咖啡。
3. 把煮好的咖啡倒进杯子。
4. 加糖或奶。 

制作茶的步骤是：

1. 把水煮开。
2. 放入茶叶。
3. 把茶倒进茶杯。
4. 加柠檬或其他调料。

   public class Coffee{
       public  void prepareRecipe()
       {
           boilWater();
           brew();
           pourInCup();
           addCondiments();
       }
       void boilWater()
       {
           System.out.println("boil water");
       }
       public void brew()
       {
           System.out.println("brew coffee");
       }
   
       void pourInCup()
       {
           System.out.println("pour in cup");
       }
       public void addCondiments()
       {
           System.out.println("add sugar");
       }
   }
   
   public class Tea  {
       public  void prepareRecipe()
       {
           boilWater();
           brew();
           pourInCup();
           addCondiments();
       }
       void boilWater()
       {
           System.out.println("boil water");
       }
       public void brew()
       {
           System.out.println("brew tea");
       }
       void pourInCup()
       {
           System.out.println("pour in cup");
       }
       public void addCondiments()
       {
           System.out.println("add lemon");
       }
   }

    

我们发现，制作两种饮料的方法有些地方是类似的，我们可以对这两个类进行抽象。

 

public abstract class CaffeineBeverage {
    public final void prepareRecipe()
    {
        boilWater();
        brew();
        pourInCup();
        addCondiments();
    }
    void boilWater()
    {
        System.out.println("boil water");
    }
    
    void pourInCup()
    {
        System.out.println("pour in cup");
    }
    
     abstract void brew();
     abstract void addCondiments();
}

public class Coffee extends CaffeineBeverage {
    public void brew()
    {
        System.out.println("brew coffee");
    }

    public void addCondiments()
    {
        System.out.println("add sugar");
    }
}

public class Client {
    public static void main(String[] args) {
        CaffeineBeverage beverage=new Coffee();
        beverage.prepareRecipe();

    }
}

 

 

例子２：

1.   javx.servlet.http.HttpServlet

HttpServlet代码,doGet等方法由子类实现。

 

public abstract class HttpServlet
extends GenericServlet
implements Serializable
{
protected void service(HttpServletRequest request,HttpServletResponse response)
    throws ServletException, IOException
  {
    if(request.getMethod().equals("GET") )
      {
    if(testConditional(request,response))
      doGet(request,response);
      }
    else if (request.getMethod().equals("HEAD") )
      {
    if(testConditional(request,response))
      doHead(request,response);
      }
    else if (request.getMethod().equals("POST") )
      {
    doPost(request,response);
      }
    else if (request.getMethod().equals("DELETE") )
      {
    doDelete(request,response);
      }
    else if (request.getMethod().equals("OPTIONS") )
      {
    doOptions(request,response);
      }
    else if (request.getMethod().equals("PUT") )
      {
    doPut(request,response);
      }
    else if (request.getMethod().equals("TRACE") )
      {
    doTrace(request,response);
      }
    else
      {
    response.sendError(HttpServletResponse.SC_BAD_REQUEST,"Method ""
               +request.getMethod()+"" is not supported by this servlet");
      }
  }
  
   protected void doGet(HttpServletRequest request,HttpServletResponse response)
    throws ServletException, IOException