Java设计模式中的策略(Strategy)模式解读

/**
 * 打折策略枚举
 */
public enum ActivityStrategyEnum {
    MEMBER(1, "普通会员"),
    GOLD_MEMBER(2, "黄金会员"),
    DIAMOND_MEMBER(3, "钻石会员"),
    ;
    private int code;
    private String name;
    ActivityStrategyEnum (int code, String name) {
        this.code = code;
        this.name = name;
    }
    /**
     * 通过code匹配对应枚举
     * @param code
     * @return
     */
    public static ActivityStrategyEnum match(int code){
        ActivityStrategyEnum strategyEnum = null;
        for (ActivityStrategyEnum item : values()){
            if(item.getCode() == code){
                strategyEnum = item;
                break;
            }
        }
        return strategyEnum;
    }
    public int getCode() {
        return code;
    }
    public String getName() {
        return name;
    }
}

//打折接口
public interface IActivityStrategyService {
    //策略code    
    int getCode();
	/**
	 * 打折
	 * @param money
	 * @return 应付金额
	 */
	BigDecimal calculate(BigDecimal money);
}
@Service("memberService ")
public class MemberService implements IActivityStrategyService {
    @Override
    public int getCode() {
        return ActivityStrategyEnum.MEMBER.getCode();
    }
	@Override
	public BigDecimal calculate(BigDecimal money) {
		//普通会员9折
		return money.multiply(new BigDecimal(0.9)).setScale(2, RoundingMode.HALF_UP);
	}
}
@Service("goldMemberService")
public class GoldMemberService implements IActivityStrategyService {
    @Override
    public int getCode() {
        return ActivityStrategyEnum.GOLD_MEMBER.getCode();
    }
	@Override
	public BigDecimal calculate(BigDecimal money) {
		//黄金会员8折
		return money.multiply(new BigDecimal(0.8)).setScale(2, RoundingMode.HALF_UP);
	}
}
@Service("diamondMemberService")
public class DiamondMemberService implements IActivityStrategyService {
    @Override
    public int getCode() {
        return ActivityStrategyEnum.DIAMOND_MEMBER.getCode();
    }
	@Override
	public BigDecimal calculate(BigDecimal money) {
		//钻石会员7折
		return money.multiply(new BigDecimal(0.7)).setScale(2, RoundingMode.HALF_UP);
	}
}

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
@Component
public class ActivityStrategyHandler implements InitializingBean, ApplicationContextAware {
    /**
     * 存放策略的map,可以理解为策略的注册中心
     */
    private final Map<Integer, IActivityStrategyService> serviceHashMap = new ConcurrentHashMap<>();
    /**
     * spring的上下文
     */
    private ApplicationContext applicationContext;
    /**
     * 将StrategyService的类都按照定义好的规则（枚举code），放入strategyServiceMap中
     *
     * @throws Exception
     */
    @Override
    public void afterPropertiesSet() throws Exception {
        Map<String, IActivityStrategyService> matchBeans = applicationContext.getBeansOfType(IActivityStrategyService.class);
        for (IActivityStrategyService strategyService : matchBeans.values()) {
            serviceHashMap.put(strategyService.getCode(), strategyService);
            System.out.println("初始化策略模式的键值对 code =" + strategyService.getCode() + " ,value=" + strategyService);
        }
    }
    /**
     * 注入applicationContext
     *
     * @param applicationContext
     * @throws BeansException
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
    /**
     * 通过枚举code获取对应对更新服务
     * @param strategyEnum
     * @return
     */
    public IActivityStrategyService getActivityService(ActivityStrategyEnum strategyEnum){
        return serviceHashMap.get(strategyEnum.getCode());
    }
}

@RestController
public class IndexController {
    @Autowired
    private ActivityStrategyHandler activityHandler;
    @GetMapping("/acitivity")
    public BigDecimal acitivity(int code) throws JsonProcessingException {
        //会员类型code
        ActivityStrategyEnum strategyEnum = ActivityStrategyEnum.match(code);
        IActivityStrategyService activityService = activityHandler.getActivityService(strategyEnum);
        //获取商品金额
        BigDecimal amount = new BigDecimal(100);
        //调用具体的打折策略算法
        BigDecimal price = activityService.calculate(amount);
        return price ;
    }
}