Spring下的策略模式的实现

Spring下策略模式的实现

在软件开发中，策略模式是一个常见的设计模式。它通过将算法封装在可互换的策略类中，来提高程序的可扩展性和灵活性。在Spring框架下，策略模式的实现得到了更加方便和简洁的实现。本文将从多个角度分析Spring下策略模式的实现，并提供相应的示例。

1.Spring的Bean注入方式实现策略模式

Spring提供了依赖注入(DI)和控制反转(IoC)的机制，通过将策略类作为Bean组件注入到上下文中，来实现策略模式。以下是一个示例代码：

```

public interface Strategy {

void doSomething();

}

@Service("strategyA")

public class ConcreteStrategyA implements Strategy {

@Override

public void doSomething() {

System.out.println("StrategyA is executed");

}

}

@Service("strategyB")

public class ConcreteStrategyB implements Strategy {

@Override

public void doSomething() {

System.out.println("StrategyB is executed");

}

}

public class Context {

@Autowired

@Qualifier("strategyA")

private Strategy strategy;

public void execute() {

strategy.doSomething();

}

}

```

2.Spring的条件注解方式实现策略模式

Spring提供了多种条件注解，例如`@ConditionalOnBean`、`@ConditionalOnMissingBean`、`@ConditionalOnProperty`等。通过条件注解的方式，来简化策略模式的实现。以下是一个示例代码：

```

public interface Strategy {

void doSomething();

}

@Service

@ConditionalOnProperty(name = "strategy.type", havingValue = "A")

public class ConcreteStrategyA implements Strategy {

@Override

public void doSomething() {

System.out.println("StrategyA is executed");

}

}

@Service

@ConditionalOnProperty(name = "strategy.type", havingValue = "B")

public class ConcreteStrategyB implements Strategy {

@Override

public void doSomething() {

System.out.println("StrategyB is executed");

}

}

public class Context {

private final Strategy strategy;

public Context(Strategy strategy) {

this.strategy = strategy;

}

public void execute() {

strategy.doSomething();

}

}

```

3.Spring的AOP方式实现策略模式

Spring提供了AOP(面向切面编程)的机制，通过定义切面和切点，来实现策略模式。以下是一个示例代码：

```

@Aspect

@Component

public class StrategyAspect {

@Autowired

@Qualifier("strategyA")

private Strategy strategyA;

@Pointcut(value = "@annotation(com.example.annotation.Strategy)")

public void pointcut() {

}

@Around("pointcut()")

public Object around(ProceedingJoinPoint joinPoint) throws Throwable {

Strategy strategy = strategyA;

MethodSignature signature = (MethodSignature) joinPoint.getSignature();

Strategy annotation = signature.getMethod().getAnnotation(Strategy.class);

if (annotation != null && "B".equals(annotation.value())) {

strategy = (Strategy) SpringUtil.getBean("strategyB");

}

return strategy.doSomething();

}

}

@Service

public class StrategyService {

@Strategy("A")

public String doSomethingByA() {

return "doSomethingByA";

}

@Strategy("B")

public String doSomethingByB() {

return "doSomethingByB";

}

}

```

通过以上三种方式实现策略模式，使得代码变得更加优雅和整洁。