过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种行为型设计模式。这种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。

一、UML类图

在这里插入图片描述

二、代码示例

过滤器接口，和一些逻辑组合的接口实现类

package filter;

public interface Criteria<T> {
    boolean matches(T candidate);

    // 只有default方法才可以有方法体
    default Criteria<T> and(Criteria<T> other) {
        return new AndCriteria<T>(this, other);
    }

    // 只有default方法才可以有方法体
    default Criteria<T> or(Criteria<T> other) {
        return new OrCriteria<T>(this, other);
    }

    class AndCriteria<T> implements Criteria<T> {
        private Criteria<T> thisCriteria, thatCriteria;

        public AndCriteria(Criteria<T> thisCriteria, Criteria<T> thatCriteria) {
            this.thisCriteria = thisCriteria;
            this.thatCriteria = thatCriteria;
        }

        @Override
        public boolean matches(T candidate) {
            return thisCriteria.matches(candidate) && thatCriteria.matches(candidate);
        }
    }

    class OrCriteria<T> implements Criteria<T> {
        private Criteria<T> thisCriteria, thatCriteria;

        public OrCriteria(Criteria<T> thisCriteria, Criteria<T> thatCriteria) {
            this.thisCriteria = thisCriteria;
            this.thatCriteria = thatCriteria;
        }

        @Override
        public boolean matches(T candidate) {
            return thisCriteria.matches(candidate) || thatCriteria.matches(candidate);
        }
    }

    class NotCriteria<T> implements Criteria<T> {
        private Criteria<T> thisCriteria;

        public NotCriteria(Criteria<T> thisCriteria) {
            this.thisCriteria = thisCriteria;
        }

        @Override
        public boolean matches(T candidate) {
            return !thisCriteria.matches(candidate);
        }
    }
}

具体的过滤器实现类

public class MaleCriteria implements Criteria<Person> {

    @Override
    public boolean matches(Person candidate) {
        return candidate.getGender().equalsIgnoreCase("male");
    }
}
public class FemaleCriteria implements Criteria<Person> {

    @Override
    public boolean matches(Person candidate) {
        return candidate.getGender().equalsIgnoreCase("female");
    }
}

public class AdultCriteria implements Criteria<Person> {

    @Override
    public boolean matches(Person candidate) {
        return candidate.getAge() >= 18;
    }
}

被过滤对象

package filter;

public class Person {
    private String name, gender;
    private int age;

    public Person(String name, String gender, int age) {
        this.name = name;
        this.gender = gender;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", gender='" + gender + '\'' +
                ", age=" + age +
                '}';
    }
}

客户类

package filter;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

public class Client {
    public static void main(String[] args) {
        List<Person> persons = Arrays.asList(
                new Person("Zhang", "female", 28),
                new Person("Wang", "male", 17),
                new Person("Li", "female", 19),
                new Person("Sun", "male", 22),
                new Person("Han", "female", 16)
        );
        System.out.println("******************** old school ********************\n");
        System.out.println("all male people --->>>");
        System.out.println(persons.stream().filter(p -> new MaleCriteria().matches(p)).collect(Collectors.toList()) + "\n");

        System.out.println("all male and adult female people --->>>");
        System.out.println(persons.stream().filter(p -> new MaleCriteria().or(new AdultCriteria().and(new FemaleCriteria())).matches(p)).collect(Collectors.toList()) + "\n");

        System.out.println("******************** new style with Predicate ********************\n");
        // 完全不需要写那么多鸡肋的Criteria，在Java 8中完全可用Predicate来替代
        Predicate<Person> isMale = p -> p.getGender().equalsIgnoreCase("male");
        Predicate<Person> isFemale = p -> p.getGender().equalsIgnoreCase("female");
        Predicate<Person> isAdult = p -> p.getAge() >= 18;
        System.out.println(persons.stream().filter(isMale).collect(Collectors.toList()));
        System.out.println(persons.stream().filter(isMale.or(isFemale.and(isAdult))).collect(Collectors.toList()));
    }
}

测试结果

******************** old school ********************

all male people --->>>
[Person{name='Wang', gender='male', age=17}, Person{name='Sun', gender='male', age=22}]

all male and adult female people --->>>
[Person{name='Zhang', gender='female', age=28}, Person{name='Wang', gender='male', age=17}, Person{name='Li', gender='female', age=19}, Person{name='Sun', gender='male', age=22}]

******************** new style with Predicate ********************

[Person{name='Wang', gender='male', age=17}, Person{name='Sun', gender='male', age=22}]
[Person{name='Zhang', gender='female', age=28}, Person{name='Wang', gender='male', age=17}, Person{name='Li', gender='female', age=19}, Person{name='Sun', gender='male', age=22}]

Process finished with exit code 0

【参考】

https://www.geeksforgeeks.org/filter-pattern-in-java/

https://www.linkedin.com/pulse/think-functional-rethinking-criteria-pattern-lambdas-sujit-kamthe/

https://www.runoob.com/design-pattern/filter-pattern.html