设计模式笔记 – 过滤器模式

过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种设计模式，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。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。

介绍

• 意图： 对同一组对象能够以不同过滤条件筛选出来
• 主要解决： 能够以不同条件或条件的组合筛选对象
• 何时使用： 一组对象需要根据属性作筛选时
• 如何解决： 使用过滤器类进行筛选
• 关键代码：
• 优点： 能使用不同过滤器的组合方便的筛选对象
• 缺点： 过滤器依赖对象的结构，对象属性变化时过滤器也需要变化，如示例中的婚姻状况增加了一种"离异"，则需要增加或修改过滤器
• 应用实例： 1、对用户信息根据不同条件如性别、婚姻状况筛选，2、对车辆根据根据不同条件如颜色、款式筛选
• 使用场景： 过滤标准较多，且分散。
• 注意事项： 过滤器应该尽量简单，复杂的过滤器应使用多个简单过滤器组合得到，这样当对象属性变化时，过滤器的改动能尽量小

示例

我们将创建一个 Person 对象、Criteria 接口和实现了该接口的实体类，来过滤 Person 对象的列表。CriteriaPatternDemo，我们的演示类使用 Criteria 对象，基于各种标准和它们的结合来过滤 Person 对象的列表。

Java 实现

创建一个类，在该类上应用标准

public class Person {
    private String name;
    private String gender;
    private String meritalStatus;
    public Person(String name, String gender, String meritalStatus) {
        this.name = name;
        this.gender = gender;
        this.meritalStatus = meritalStatus;
    }
    public String getName() {
        return name;
    }
    public String getGender() {
        return gender;
    }
    public String getMeritalStatus() {
        return meritalStatus;
    }
}

为标准（Criteria）创建一个接口

import java.util.List;

public interface Criteria {
    public List<Person> meetCriteria(List<Person> persons);
}

创建实现了Criteria接口的实体类

import java.util.ArrayList;
import java.util.List;

public class CriteriaMale implements Criteria {
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> malePersons = new ArrayList<Person>();
        for (Person person : persons) {
            if (person.getGender().equalsIgnoreCase("MALE")) {
                malePerson.add(person);
            }
        }
        return malePersons;
    }
}

import java.util.ArrayList;
import java.util.List;

public class CriteriaFemale implements Criteria {
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> femalePersons = new ArrayList<Person>();
        for (Person person : persons) {
            if (person.getGender().equalsIgnoreCase("FEMALE")) {
                femalePerson.add(person);
            }
        }
        return femalePersons;
    }
}

import java.util.ArrayList;
import java.util.List;

public class CriteriaSingle implements Criteria {
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> singlePersons = new ArrayList<Person>();
        for (Person person : persons) {
            if (person.getMaritalStatus().equalsIgnoreCase("SINGLE")) {
                singlePersons.add(person);
            }
        }
        return singlePersons;
    }
}

import java.util.List;

public class AndCriteria implements Criteria {
    private Criteria criteria;
    private Criteria otherCriteria;

    public AndCriteria(Criteria criteria, Criteria otherCriteria) {
        this.criteria = criteria;
        this.otherCriteria = otherCriteria;
    }

    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);
        return otherCriteria.meetCriteria(firstCriteriaPersons);
    }
}

import java.util.List;

public class OrCriteria implements Criteria {
    private Criteria criteria;
    private Criteria otherCriteria;

    public AndCriteria(Criteria criteria, Criteria otherCriteria) {
        this.criteria = criteria;
        this.otherCriteria = otherCriteria;
    }

    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);
        List<Person> otherCriteriaPersons = otherCriteria.meetCriteria(persons);

        for (Person person : otherCriteriaPersons) {
            if (!firstCriteriaPersons.contains(person)){
                firstCriteriaPersons.add(person);
            }
        }
        return firstCriteriaPersons
    }
}

使用不同的标准（Criteria）和它们的结合来过滤Person对象的列表

import java.util.ArrayList; 
import java.util.List;

public class CriteriaPatternDemo {
    public static void main(String[] args) {
        List<Person> persons = new ArrayList<Person>();

        persons.add(new Person("Robert", "Male", "Single"));
        persons.add(new Person("John", "Male", "Married"));
        persons.add(new Person("Laura", "Female", "Married"));
        persons.add(new Person("Diana", "Female", "Single"));
        persons.add(new Person("Mike", "Male", "Single"));
        persons.add(new Person("Bobby", "Male", "Single"));

        Criteria male = new CriteriaMale();
        Criteria female = new CriteriaFemale();
        Criteria single = new CriteriaSingle();
        Criteria singleMale = new AndCriteria(single, male);
        Criteria singleOrFemale = new OrCriteria(single, female);

        System.out.println("Males: ");
        printPersons(male.meetCriteria(persons));

        System.out.println("\nFemales: ");
        printPersons(female.meetCriteria(persons));

        System.out.println("\nSingle Males: ");
        printPersons(singleMale.meetCriteria(persons));

        System.out.println("\nSingle Or Females: ");
        printPersons(singleOrFemale.meetCriteria(persons));
    }

    public static void printPersons(List<Person> persons){
        for (Person person : persons) {
            System.out.println("Person : [ Name : " + person.getName() 
                +", Gender : " + person.getGender() 
                +", Marital Status : " + person.getMaritalStatus()
                +" ]");
        }
    }      
}

Python 实现

import abc

class Person(object):
    def __init__(self, name, gender, marital_status):
        self.name = name
        self.gender = gender
        self.marital_status = marital_status

    def get_name(self) -> str:
        return self.name

    def get_gender(self) -> str:
        return self.gender

    def get_marital_status(self) -> str:
        return self.marital_status

class Criteria(abc.ABC):
    @abc.abstractmethod
    def meet_criteria(self, persons) -> [Person]: ...

class CriteriaMale(Criteria):
    def meet_criteria(self, persons):
        male_person = []
        for person in persons:
            if person.get_gender().upper() == "MALE":
                male_person.append(person)
        return male_person

class CriteriaFemale(Criteria):
    def meet_criteria(self, persons):
        female_person = []
        for person in persons:
            if person.get_gender().upper() == "FEMALE":
                female_person.append(person)
        return female_person

class CriteriaSingle(Criteria):
    def meet_criteria(self, persons):
        single_person = []
        for person in persons:
            if person.get_marital_status().upper() == "SINGLE":
                single_person.append(person)
        return single_person

class AndCriteria(Criteria):
    def __init__(self, criteria, other_criteria):
        self.criteria = criteria
        self.other_criteria = other_criteria

    def meet_criteria(self, persons):
        first_criteria_persons = self.criteria.meet_criteria(persons)
        return self.other_criteria.meet_criteria(first_criteria_persons)

class OrCriteria(Criteria):
    def __init__(self, criteria, other_criteria):
        self.criteria = criteria
        self.other_criteria = other_criteria

    def meet_criteria(self, persons):
        first_criteria_persons = self.criteria.meet_criteria(persons)
        other_criteria_persons = self.other_criteria.meet_criteria(persons)

        for person in other_criteria_persons:
            if person not in first_criteria_persons:
                first_criteria_persons.append(person)

        return first_criteria_persons

def print_persons(persons):
    for person in persons:
        print(f"Person: [Name: {person.get_name()}, "
              f"Gender: {person.get_gender()}, "
              f"Marital Status: {person.get_marital_status()}]")

if __name__ == "__main__":
    persons = []
    persons.append(Person("Robert", "Male", "Single"))
    persons.append(Person("John", "Male", "Married"))
    persons.append(Person("Laura", "Female", "Married"))
    persons.append(Person("Diana", "Female", "Single"))
    persons.append(Person("Mike", "Male", "Single"))
    persons.append(Person("Bobby", "Male", "Single"))

    male = CriteriaMale()
    female = CriteriaFemale()
    single = CriteriaSingle()
    single_male = AndCriteria(single, male)
    single_or_female = OrCriteria(single, female)

    print("Male: ")
    print_persons(male.meet_criteria(persons))

    print("Female: ")
    print_persons(female.meet_criteria(persons))

    print("Single Males: ")
    print_persons(single_male.meet_criteria(persons))

    print("Single Or Females: ")
    print_persons(single_or_female.meet_criteria(persons))