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。

实现

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。

步骤 1

创建一个类，在该类上应用标准。

Person.java

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

步骤 2

为标准（Criteria）创建一个接口。

Criteria.java

import java.util.List;
public interface Criteria {
    public ListPerson> meetCriteria(ListPerson> persons);
}

步骤 3

创建实现了 Criteria 接口的实体类。

CriteriaMale.java

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

CriteriaFemale.java

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

CriteriaSingle.java

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

AndCriteria.java

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 ListPerson> meetCriteria(ListPerson> persons) {
        ListPerson> firstCriteriaPersons = criteria.meetCriteria(persons);
        return otherCriteria.meetCriteria(firstCriteriaPersons);
    }
}

OrCriteria.java

import java.util.List;
public class OrCriteria implements Criteria {
    private Criteria criteria;
    private Criteria otherCriteria;
    public OrCriteria(Criteria criteria, Criteria otherCriteria) {
        this.criteria = criteria;
        this.otherCriteria = otherCriteria;
    }
    @Override
    public ListPerson> meetCriteria(ListPerson> persons) {
        ListPerson> firstCriteriaItems = criteria.meetCriteria(persons);
        ListPerson> otherCriteriaItems = otherCriteria.meetCriteria(persons);
        for (Person person : otherCriteriaItems) {
            if(!firstCriteriaItems.contains(person)){
                firstCriteriaItems.add(person);
            }
        }
        return firstCriteriaItems;
    }
}

步骤4

使用不同的标准（Criteria）和它们的结合来过滤 Person 对象的列表。

CriteriaPatternDemo.java

import java.util.ArrayList;
import java.util.List;
public class CriteriaPatternDemo {
    public static void main(String[] args) {
        ListPerson> persons = new ArrayListPerson>();
        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(ListPerson> persons){
        for (Person person : persons) {
            System.out.println("Person : [ Name : " + person.getName()
            +", Gender : " + person.getGender()
            +", Marital Status : " + person.getMaritalStatus()
            +" ]");
        }
    }
}

步骤 5

执行程序，输出结果：

Males: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : John, Gender : Male, Marital Status : Married ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]

Females: 
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]
Person : [ Name : Diana, Gender : Female, Marital Status : Single ]

Single Males: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]

Single Or Females: 
Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
Person : [ Name : Diana, Gender : Female, Marital Status : Single ]
Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]