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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 List
   
     meetCriteria(List
    
      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 List
   
     meetCriteria(List
    
      persons) {      List
     
       malePersons = new ArrayList
      
       ();       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 List
   
     meetCriteria(List
    
      persons) {      List
     
       femalePersons = new ArrayList
      
       ();       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 List
   
     meetCriteria(List
    
      persons) {      List
     
       singlePersons = new ArrayList
      
       ();       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 List
   
     meetCriteria(List
    
      persons) {      List
     
       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 List
   
     meetCriteria(List
    
      persons) {      List
     
       firstCriteriaItems = criteria.meetCriteria(persons);      List
      
        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) {      List
   
     persons = new ArrayList
    
     ();       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
     
       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 ]

总结

过滤模式的实现在java8里面有典型的应用方法就是分组操作，可以根据指定的指标进行分组筛选。

Map
   
    > groupMap = persons.stream().collect(Collectors.groupingBy(Person::getGender));groupMap.forEach((k, v) -> {    System.out.println(k);    v.forEach(System.out::println);});
   

得到的结果形式就是：

•  k：是分组的指标，上面代码中的 gender
•  v：是一个list的集合对象，就是 personList

可以参考：

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