Design Patterns - Filter Pattern（译）

原文链接
译者：smallclover
个人翻译，水平有限，如有错误欢迎指出，谢谢！

设计模式-过滤模式

过滤模式或者标准模式能通过逻辑操作，开发者可以以松耦合的方式通过使用不同的标准和过滤链来过滤一组对象。这种类型的设计模式来源于结构模式，它通过组合多种不同的标准来获得单一的标准。

实现

我们将创建一个Person对象以及Criteria接口。并且创建实现Criteria接口的具体类，这些具体类负责过滤Person对象列表。CriteriaPatternDemo，我们的demo类使用criteria对象基于不同的标准以及它们的组合来过滤Person对象列表

第一步

创建一个标准的应用类
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;
   }    
}

第二步

创建一个Criteria接口
Criteria.java

import java.util.List;

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

第三步

创建具体类实现Criteria接口

译者注：
CriteriaMale类 根据Male标准过滤
CriteriaFemale类 根据Female标准过滤
CriteriaSingle类 根据Single标准过滤
AndCriteria类组合两种标准criteria, otherCriteria，同时满足两个标准的Person对象会被过滤出来。
OrCriteria类组合两种标准criteria, otherCriteria，满足otherCriteria基础之上，选择性的满足criteria标准，过滤Person对象

CriteriaMale.java

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")){
            malePersons.add(person);
         }
      }
      return malePersons;
   }
}

CriteriaFemale.java

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")){
            femalePersons.add(person);
         }
      }
      return femalePersons;
   }
}

CriteriaSingle.java

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

public class CriteriaSingle implements Criteria {

   @Override
   public List<Person> meetCriteria(List<Person> persons) {
      List<Person> single  -Persons = new ArrayList<Person>(); 
      
      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<Person> meetCriteria(List<Person> persons) {
   
      List<Person> 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<Person> meetCriteria(List<Person> persons) {
      List<Person> firstCriteriaItems = criteria.meetCriteria(persons);
      List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persons);

      for (Person person : otherCriteriaItems) {
         if(!firstCriteriaItems.contains(person)){
            firstCriteriaItems.add(person);
         }
      }    
      return firstCriteriaItems;
   }
}

第四步

使用不同的标准以及它们的组合来筛选对象
CriteriaPatternDemo.java

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() + " ]");
      }
   }      
}

第五步

确认输出

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 ]

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