Java過濾器模式

過濾器模式(Filter Pattern)或標準模式(Criteria Pattern)是一種設計模式，這種模式允許開發人員使用不同的標準來過濾一組對象，通過邏輯運算以解耦的方式把它們連接起來。這種類型的設計模式屬于結構型模式，它結合多個標準來獲得單一標準。

實現

我們將創建一個 Person 對象、Criteria 接口和實現了該接口的實體類，來過濾 Person 對象的列表。CriteriaPatternDemo，我們的演示類使用 Criteria 對象，基于各種標準和它們的結合來過濾 Person 對象的列表。

步驟 1

創建一個類，在該類上應用標準。

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;
   }  
}

步驟 2

為標準(Criteria)創建一個接口。

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

步驟 3

創建實現了 Criteria 接口的實體類。

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;
   }
}

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;
   }
}

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;
   }
}

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);
   }
}

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;
   }
}

步驟4

使用不同的標準(Criteria)和它們的結合來過濾 Person 對象的列表。

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()
            +" ]");
      }
   }      
}

步驟 5

執行程序，輸出結果：

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 ]