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)
java
// 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
java
// 过滤器接口
interface Filter {
List<Apple> filter(List<Apple> apples);
}
- 具体过滤器实现
java
// 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)
java
// 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
java
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
java
// 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
}
}
过滤器模式应用场景
- 数据筛选:
- 电商商品筛选(价格、品牌、评分)
- 日志过滤(错误级别、时间范围)
- 权限系统:
- 用户角色过滤(管理员、VIP用户)
- 数据权限过滤(部门、区域)
- 数据清洗:
- 去除无效数据(空值、异常值)
- 敏感信息过滤(手机号脱敏)
过滤器模式优势
- 灵活组合条件:通过组合多个过滤器实现复杂逻辑
- 解耦过滤逻辑:每个过滤器独立维护,新增条件无需修改已有代码
- 可复用性高:同一过滤器可用于不同场景(如"北京用户筛选"可用于报表和推送)