过滤模式（ Filter Pattern）

过滤模式或标准模式是一种设计模式，使开发人员能够使用不同的标准过滤一组对象，并通过逻辑操作以分离的方式将它们链接起来。 这种类型的设计模式属于结构模式，因为该模式结合了多个标准以获得单一标准。

实现 (Implementation)

我们将创建一个Person对象， Criteria接口和实现此接口的具体类来过滤Person对象列表。 CriteriaPatternDemo ，我们的演示类使用Criteria对象根据各种标准及其组合过滤Person对象列表。

Step 1

创建要应用条件的类。

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;
   }	
}

Step 2

为Criteria创建一个界面。

Criteria.java

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

Step 3

创建实现Criteria接口的具体类。

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> singlePersons = 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;
   }
}

Step4

使用不同的Criteria及其组合来过滤掉人员。

CriteriaPatternDemo.java

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() + " ]");
      }
   }      
}

Step 5

验证输出。

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 ]