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【设计模式】过滤器模式

news 来源：原创 2025/4/30 22:14:50

过滤器顾名思义，定义一些过滤规则，将符合要求的内容筛选，就比如过滤不同大小或者不同颜色的水果，需要颜色和大小过滤器，筛选条件独立为对象，可以通过灵活组合形成过滤链条。避免大量使用判断语句。

案例代码：筛选不同颜色的苹果

被过滤对象（苹果）

// 苹果对象
class Apple {
    private String color;
    private int weight;

    public Apple(String color, int weight) {
        this.color = color;
        this.weight = weight;
    }

    public String getColor() { return color; }
    public int getWeight() { return weight; }
}

过滤器接口

// 过滤器接口
interface Filter {
    List<Apple> filter(List<Apple> apples);
}

具体过滤器实现

// 颜色过滤器（筛选红色苹果）
class ColorFilter implements Filter {
    public List<Apple> filter(List<Apple> apples) {
        List<Apple> result = new ArrayList<>();
        for (Apple apple : apples) {
            if ("red".equalsIgnoreCase(apple.getColor())) {
                result.add(apple);
            }
        }
        return result;
    }
}

// 重量过滤器（筛选重量大于150g的苹果）
class WeightFilter implements Filter {
    public List<Apple> filter(List<Apple> apples) {
        List<Apple> result = new ArrayList<>();
        for (Apple apple : apples) {
            if (apple.getWeight() > 150) {
                result.add(apple);
            }
        }
        return result;
    }
}

组合过滤器（多条件筛选）

// 组合过滤器（同时满足多个条件）
class AndFilter implements Filter {
    private Filter filter1;
    private Filter filter2;

    public AndFilter(Filter filter1, Filter filter2) {
        this.filter1 = filter1;
        this.filter2 = filter2;
    }

    public List<Apple> filter(List<Apple> apples) {
        List<Apple> temp = filter1.filter(apples);
        return filter2.filter(temp);
    }
}

使用过滤器模式

public class FilterDemo {
    public static void main(String[] args) {
        List<Apple> apples = Arrays.asList(
            new Apple("Red", 200),
            new Apple("Green", 160),
            new Apple("Red", 140)
        );

        // 单条件筛选：红色苹果
        Filter colorFilter = new ColorFilter();
        List<Apple> redApples = colorFilter.filter(apples);
        System.out.println("红色苹果数量：" + redApples.size()); // 输出：2

        // 组合筛选：红色且重量>150g
        Filter weightFilter = new WeightFilter();
        Filter andFilter = new AndFilter(colorFilter, weightFilter);
        List<Apple> result = andFilter.filter(apples);
        System.out.println("符合条件的苹果数量：" + result.size()); // 输出：1
    }
}

应用场景案例：用户权限过滤
场景描述
筛选出同时满足以下条件的用户：

年龄在18岁以上
所在城市为“北京”
注册时间在2023年以后
代码实现

// 用户对象
class User {
    private String name;
    private int age;
    private String city;
    private LocalDate registerDate;

    public User(String name, int age, String city, LocalDate registerDate) {
        this.name = name;
        this.age = age;
        this.city = city;
        this.registerDate = registerDate;
    }

    // Getter方法省略...
}

// 年龄过滤器
class AgeFilter implements Filter {
    private int minAge;

    public AgeFilter(int minAge) {
        this.minAge = minAge;
    }

    public List<User> filter(List<User> users) {
        List<User> result = new ArrayList<>();
        for (User user : users) {
            if (user.getAge() >= minAge) {
                result.add(user);
            }
        }
        return result;
    }
}

// 城市过滤器
class CityFilter implements Filter {
    private String city;

    public CityFilter(String city) {
        this.city = city;
    }

    public List<User> filter(List<User> users) {
        List<User> result = new ArrayList<>();
        for (User user : users) {
            if (city.equalsIgnoreCase(user.getCity())) {
                result.add(user);
            }
        }
        return result;
    }
}

// 注册时间过滤器
class DateFilter implements Filter {
    private LocalDate startDate;

    public DateFilter(LocalDate startDate) {
        this.startDate = startDate;
    }

    public List<User> filter(List<User> users) {
        List<User> result = new ArrayList<>();
        for (User user : users) {
            if (user.getRegisterDate().isAfter(startDate)) {
                result.add(user);
            }
        }
        return result;
    }
}

// 使用示例
public class UserFilterDemo {
    public static void main(String[] args) {
        List<User> users = Arrays.asList(
            new User("张三", 25, "北京", LocalDate.of(2024, 1, 1)),
            new User("李四", 17, "上海", LocalDate.of(2024, 2, 1)),
            new User("王五", 30, "北京", LocalDate.of(2022, 5, 1))
        );

        // 创建过滤器
        Filter ageFilter = new AgeFilter(18);
        Filter cityFilter = new CityFilter("北京");
        Filter dateFilter = new DateFilter(LocalDate.of(2023, 1, 1));

        // 组合过滤：年龄>=18 && 城市=北京 && 注册时间>2023
        Filter combinedFilter = new AndFilter(ageFilter, 
            new AndFilter(cityFilter, dateFilter));

        List<User> validUsers = combinedFilter.filter(users);
        System.out.println("有效用户数量：" + validUsers.size()); // 输出：1
    }
}