行为型设计模式-模板方法 Template Method

简介

父类抽象类定义大的处理流程，部分细节做成抽象方法，留给子类去实现。

如Java的JUnit中， setUp tearDown方法都是留给具体的测试用例来写，Servlet中service处理了一个请求的大部分工作，留下doGet和doPost给业务自定义处理。

另外callback一般分两种方式：同步回调、异步回调，其中同步回调类似于模板方法模式，异步回调类似于观察者模式。

模板方法要基于继承，而回调更类似组合，

角色

• 抽象模板类

  定义大的处理流程，留出部分方法给具体类实现

• 具体模板类

  实现具体的处理逻辑

类图

如图，ConcreteClass实现了一些具体逻辑

代码

abstract class AbstractClass
{
    final public function templateMethod(): void
    {
        $this->baseOperation1();
        $this->requiredOperations1();
        $this->baseOperation2();
        $this->hook1();
        $this->requiredOperation2();
        $this->baseOperation3();
        $this->hook2();
    }

    protected function baseOperation1(): void
    {
        echo "AbstractClass says: I am doing the bulk of the work\n";
    }

    protected function baseOperation2(): void
    {
        echo "AbstractClass says: But I let subclasses override some operations\n";
    }

    protected function baseOperation3(): void
    {
        echo "AbstractClass says: But I am doing the bulk of the work anyway\n";
    }

    abstract protected function requiredOperations1(): void;

    abstract protected function requiredOperation2(): void;

    protected function hook1(): void { }

    protected function hook2(): void { }
}

class ConcreteClass1 extends AbstractClass
{
    protected function requiredOperations1(): void
    {
        echo "ConcreteClass1 says: Implemented Operation1\n";
    }

    protected function requiredOperation2(): void
    {
        echo "ConcreteClass1 says: Implemented Operation2\n";
    }
}

class ConcreteClass2 extends AbstractClass
{
    protected function requiredOperations1(): void
    {
        echo "ConcreteClass2 says: Implemented Operation1\n";
    }

    protected function requiredOperation2(): void
    {
        echo "ConcreteClass2 says: Implemented Operation2\n";
    }

    protected function hook1(): void
    {
        echo "ConcreteClass2 says: Overridden Hook1\n";
    }
}

function clientCode(AbstractClass $class)
{
    $class->templateMethod();
}

echo "Same client code can work with different subclasses:\n";
clientCode(new ConcreteClass1());

echo "Same client code can work with different subclasses:\n";
clientCode(new ConcreteClass2());

output:

Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway
Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway