2.2 过滤器模式

1.定义
过滤器模式允许开发人员使用不同的标准来过滤一组对象，通过逻辑运算以解耦的方式把它们连接起来。

2.好处
提高程序的可扩展性，假如新增过滤规则，只需要再编写一个实现过滤器接口的类即可。

3.案例
(1).需求描述
货源存在cargoId、cargoName和cargoCategory等字段，根据业务需求需要对货源字段进行过滤，如果有任意过滤规则不满足，则该货源不允许上架。

(2).Cargo

@Data
@AllArgsConstructor
public class Cargo {
    private Long cargoId;

    private String cargoName;

    private String cargoCategory;
}

(3).Cargo

public interface ICargoFilter {
    //过滤器执行顺序，值越小越先执行
    int getOrder();

    //过滤逻辑
    boolean filter(Cargo cargo);
}

@Component
public class CargoIdCargoFilter implements ICargoFilter {
    public int getOrder() {
        return 30;
    }

    public boolean filter(Cargo cargo) {
        if (cargo.getCargoId() < 0) {
            System.out.println("cargoId不合法");
            return false;
        }
        return true;
    }
}

@Component
public class CargoNameCargoFilter implements ICargoFilter {
    public int getOrder() {
        return 20;
    }

    public boolean filter(Cargo cargo) {
        if ("".equals(cargo.getCargoName())) {
            System.out.println("货源名称为空");
            return false;
        }
        return true;
    }
}

@Component
public class CategoryCargoFilter implements ICargoFilter {
    public int getOrder() {
        return 10;
    }

    public boolean filter(Cargo cargo) {
        if ("毒品".equals(cargo.getCargoCategory())) {
            System.out.println("货源类别为禁运物品");
            return false;
        }
        return true;
    }
}

(4).CargoFilterServiceLocator

@Component
public class CargoFilterServiceLocator implements ApplicationContextAware {
    /**
     * 存储ICargoFilter接口的所有实现类
     */
    private Map<String, ICargoFilter> cargoFilterMap;
    private List<ICargoFilter> cargoFilterList;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        cargoFilterMap = applicationContext.getBeansOfType(ICargoFilter.class);
        cargoFilterList = new ArrayList<>(cargoFilterMap.values());
    }

    /**
     * 获取所有实现类
     *
     * @return
     */
    public List<ICargoFilter> getAllList() {
        Collections.sort(cargoFilterList, new Comparator<ICargoFilter>() {
            @Override
            public int compare(ICargoFilter o1, ICargoFilter o2) {
                return o1.getOrder() - o2.getOrder();
            }
        });
        return cargoFilterList;
    }
}

(5).测试

@RunWith(SpringRunner.class)
@SpringBootTest
class SpringBootDemoApplicationTests {
    @Autowired
    private CargoFilterServiceLocator cargoFilterServiceLocator;

    @Test
    void contextLoads() {

    }

    @Test
    void test() {
        Cargo cargo = new Cargo(-10000l,"水果","毒品");
        List<ICargoFilter> cargoFilters = cargoFilterServiceLocator.getAllList();
        for(ICargoFilter cargoFilter:cargoFilters){
            if(!cargoFilter.filter(cargo)){
                break;
            }
        }
    }
}

货源类别为禁运物品