GOF设计模式之STRATEGY(策略)

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概述

本文将和读者一起来理解GOF设计模式之OBSERVER(代理)。同样，本文将用JAVA对GOF中的示例代码改些，同时附上测试用例。

模式结构

GOF对STRATEGY的模式结构描述如
这里写图片描述
策略Strategy提供了AlgorithmInterface()接口，而其继承者ConcreteStrategy们将实现AlgorithmInterface()的多态。最后，Context初始化不同的strategy并调用strategy.AlgorithmInterface来实现策略。
看了这个模式结构图，有没有感觉就是一个类的多态。在子类中通过多态的方式实现了不同的方法实现策略。实际上就是这么一回事。

代码示例

为了简单明了地实现策略模式，笔者对示例代码做了瘦身。类结构如
这里写图片描述
Composition在构造函数中注入Compositor实例，并在Repair接口中调用compositor.Compose()实现策略。
完整代码如

package gof.composition;import org.springframework.beans.factory.annotation.Qualifier;import org.springframework.stereotype.Component;@Component@Qualifier("arrayCompositor")public class ArrayCompositor extends Compositor {    @Override    public void Compose() {        System.out.println("compse in ArrayCompositor");    }}

package gof.composition;import org.springframework.context.annotation.Scope;import org.springframework.stereotype.Component;@Component@Scope("prototype")public class Composition {    public Compositor compositor;    public Composition(Compositor compositor) {        this.compositor = compositor;    }    public void Repair() {        this.compositor.Compose();    }}

package gof.composition;abstract public class Compositor {    public abstract void Compose();}

package gof.composition;import org.springframework.beans.factory.annotation.Qualifier;import org.springframework.stereotype.Component;@Component@Qualifier("simpleCompositor")public class SimpleCompositor extends Compositor {    @Override    public void Compose() {        System.out.println("compose in SimpleCompositor");    }}

package gof.composition;import org.springframework.beans.factory.annotation.Qualifier;import org.springframework.stereotype.Component;@Component@Qualifier("texCompositor")public class TeXCompositor extends Compositor {    @Override    public void Compose() {        System.out.println("compse in TeXCompositor");    }}

测试用例

package gof.composition;import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.Configuration;@Configuration@ComponentScanpublic class CompositionConfig {}

package gof.composition;import org.junit.Rule;import org.junit.Test;import org.junit.contrib.java.lang.system.StandardOutputStreamLog;import org.junit.runner.RunWith;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.ApplicationContext;import org.springframework.test.context.ContextConfiguration;import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import org.springframework.test.context.support.AnnotationConfigContextLoader;import gof.composition.ArrayCompositor;import gof.composition.Composition;import gof.composition.SimpleCompositor;import gof.composition.TeXCompositor;@ContextConfiguration(classes=CompositionConfig.class,loader=AnnotationConfigContextLoader.class)@RunWith(SpringJUnit4ClassRunner.class)public class CompositionTest {    @Rule    public final StandardOutputStreamLog log = new StandardOutputStreamLog();    @Autowired    protected ApplicationContext context;    @Autowired    protected ArrayCompositor arrCompositor;    @Autowired    protected SimpleCompositor simpCompositor;      @Autowired    protected TeXCompositor texCompositor;    @Test    public void testArrayCom() {        Composition comp = (Composition) this.context.getBean("composition", this.arrCompositor);        comp.Repair();    }    @Test    public void testSimpComp() {        Composition comp = (Composition) this.context.getBean("composition", this.simpCompositor);        comp.Repair();          }    @Test    public void testTexComp() {        Composition comp = (Composition) this.context.getBean("composition", this.texCompositor);        comp.Repair();          }}

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