设计模式24 - 过滤器模式

作者：billy
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过滤器模式

过滤器模式(Filter Pattern)，又叫标准模式(Criteria Pattern)，是一种结构型模式，通过结合多个标准来获得单一标准。
这种设计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。

使用场景

当你在一个很庞大的数据量中查找一些东西时，可以使用过滤器模式制定过滤规则，然后根据指定的标准进行过滤，得到符合条件的数据。

优缺点

• 优点：
  1、体现了各功能模块的“黑盘”特性及高内聚、低耦合的特点。
  2、可以将整个系统的输入，输出行为看成是多个过滤器行为的简单合成。
  3、支持软件功能模块的重用。
  4、便于系统维护：新的过滤器可以添加到现有系统中来，旧的可以由改进的过滤器替换。
  5、支持某些特定的分析，如吞吐量计算、死锁检测等。
  6、支持并行操作，每个过滤器可以作为一个单独的任务完成。

• 缺点：
  1、通常导致系统处理过程的成批操作。
  2、需要设计者协调两个相对独立但又存在关系的数据流。
  3、可能需要每个过滤器自己完成数据解析和合成工作（如加密和解密），从而导致系统性能下降，并增加了过滤器具体实现的复杂性。

注意事项

1、构建过滤规则时不要太繁琐。
2、注意区分过滤和拦截的功能差异。

UML结构图

代码实现

person.h
构建类 Person，可输出自己的属性，判断是否在一个数组中

#include <string>
#include <vector>
#include <iostream>
using namespace std;

class Person
{
public:
    Person(string name, string gender, int age) : name(name), gender(gender), age(age) {}

    void printf()
    {
        cout << "student name: " + name +
                ", gender: " + gender +
                ", age: " + std::to_string(age) << endl;
    }

    bool judVec(std::vector<Person*> vec)
    {
        auto iter = std::find(std::begin(vec), std::end(vec), this);
        return (iter == std::end(vec));
    }

    string getName() { return this->name; }

    string getGender() { return this->gender; }

    int getAge() { return this->age; }

private:
    string name;
    string gender;
    int age;
};

interface.h
创建抽象类 - 过滤器；创建实体类 - 过滤器、男性过滤器、女性过滤器、年龄过滤器
男性和年龄过滤器、女性或年龄过滤器

#include "person.h"
#include <algorithm>

class Criteria  //基类-过滤器
{
public:
    Criteria() {}
    virtual ~Criteria() {}

    virtual std::vector<Person *> filter(std::vector<Person *> vector) = 0;
};

class MaleCriteria: public Criteria //子类-男性过滤器
{
public:
    std::vector<Person *> filter(std::vector<Person *> vector)
    {
        std::vector<Person *> result;

        for(size_t i = 0; i < vector.size(); i++)
        {
            if(vector.at(i)->getGender() == "male")
            {
                result.push_back(vector.at(i));
            }
        }

        return result;
    }
};

class FemaleCriteria: public Criteria   //子类-女性过滤器
{
public:
    std::vector<Person *> filter(std::vector<Person *> vector)
    {
        std::vector<Person *> result;

        for(size_t i = 0; i < vector.size(); i++)
        {
            if(vector.at(i)->getGender() == "female")
            {
                result.push_back(vector.at(i));
            }
        }

        return result;
    }
};

class AgeCriteria: public Criteria  //子类-年龄过滤器
{
public:
    std::vector<Person *> filter(std::vector<Person *> vector)
    {
        std::vector<Person *> result;

        for(size_t i = 0; i < vector.size(); i++)
        {
            if(vector.at(i)->getAge() > 18) {
                result.push_back(vector.at(i));
            }
        }

        return result;
    }
};

class AndCriteria: public Criteria  //子类-与 && 过滤器
{
public:
    AndCriteria(Criteria *firstCriteria, Criteria *secondCriteria): firstCriteria(firstCriteria), secondCriteria(secondCriteria) {}

    std::vector<Person *> filter(std::vector<Person *> vector)
    {
        std::vector<Person *> firstvector = firstCriteria->filter(vector);
        return secondCriteria->filter(firstvector);
    }

private:
    Criteria *firstCriteria;
    Criteria *secondCriteria;
};

class OrCriteria: public Criteria   //子类- 或 || 过滤器
{
public:
    OrCriteria(Criteria *firstCriteria, Criteria *secondCriteria) : firstCriteria(firstCriteria), secondCriteria(secondCriteria) {}

    std::vector<Person *> filter(std::vector<Person *> vector)
    {
        std::vector<Person *> firstvector = firstCriteria->filter(vector);
        std::vector<Person *> secondvector = secondCriteria->filter(vector);

        for(auto it: firstvector)
        {
            if (it->judVec(secondvector))
            {
                secondvector.push_back(it);
            }
        }

        return secondvector;
    }

private:
    Criteria *firstCriteria;
    Criteria *secondCriteria;
};

main.cpp
实例应用 - 根据不同的过滤规则获取不同的数据

#include "interface.h"

int main()
{
    std::vector<Person *> vector;
    Person *stu1 = new Person("Billy", "male", 25);
    Person *stu2 = new Person("Kitty", "female", 24);
    Person *stu3 = new Person("Alice", "female", 23);
    Person *stu4 = new Person("Ben", "male", 17);
    Person *stu5 = new Person("Jeason", "male", 18);
    Person *stu6 = new Person("Jon", "male", 20);
    Person *stu7 = new Person("Miss", "female", 13);
    Person *stu8 = new Person("Abbey", "female", 14);

    vector.push_back(stu1);
    vector.push_back(stu2);
    vector.push_back(stu3);
    vector.push_back(stu4);
    vector.push_back(stu5);
    vector.push_back(stu6);
    vector.push_back(stu7);
    vector.push_back(stu8);

    Criteria *maleCriteria = new MaleCriteria();
    Criteria *femaleCriteria = new FemaleCriteria();
    Criteria *ageCriteria = new AgeCriteria();
    Criteria *andCriteria = new AndCriteria(maleCriteria, ageCriteria);
    Criteria *orCriteria = new OrCriteria(femaleCriteria, ageCriteria);

    std::vector<Person *> malevector = maleCriteria->filter(vector);
    std::vector<Person *> femalevector = femaleCriteria->filter(vector);
    std::vector<Person *> agevector = ageCriteria->filter(vector);
    std::vector<Person *> andvector = andCriteria->filter(vector);
    std::vector<Person *> orvector = orCriteria->filter(vector);

    cout << "male:" << endl;
    for(auto it: malevector)
    {
        it->printf();
    }

    cout << endl << "female:" << endl;
    for(auto it: femalevector)
    {
        it->printf();
    }

    cout << endl << "age > 18:" << endl;
    for(auto it: agevector)
    {
        it->printf();
    }

    cout << endl << "male and age > 18:" << endl;
    for(auto it: andvector)
    {
        it->printf();
    }

    cout << endl << "female or age > 18:" << endl;
    for(auto it: orvector)
    {
        it->printf();
    }

    return 0;
}

运行结果：
male:
student name: Billy, gender: male, age: 25
student name: Ben, gender: male, age: 17
student name: Jeason, gender: male, age: 18
student name: Jon, gender: male, age: 20

female:
student name: Kitty, gender: female, age: 24
student name: Alice, gender: female, age: 23
student name: Miss, gender: female, age: 13
student name: Abbey, gender: female, age: 14

age > 18:
student name: Billy, gender: male, age: 25
student name: Kitty, gender: female, age: 24
student name: Alice, gender: female, age: 23
student name: Jon, gender: male, age: 20

male and age > 18:
student name: Billy, gender: male, age: 25
student name: Jon, gender: male, age: 20

female or age > 18:
student name: Billy, gender: male, age: 25
student name: Kitty, gender: female, age: 24
student name: Alice, gender: female, age: 23
student name: Jon, gender: male, age: 20
student name: Miss, gender: female, age: 13
student name: Abbey, gender: female, age: 14