代碼詳解設計模式--過濾器模式

過濾器模式

  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。最常見的應用如MyBatis中。

// 實體
@Data
@AllArgsConstructor
public class Person {
   private String name;
   private String gender;
   private String maritalStatus;
}

// 條件接口
public interface Criteria {
   public List<Person> filter(List<Person> persons);
}

// 男性條件
public class MaleCriteria implements Criteria {
   @Override
   public List<Person> filter(List<Person> persons) {
      List<Person> malePersons = new ArrayList<Person>(); 
      for (Person person : persons) {
         if(person.getGender().equalsIgnoreCase("MALE")){
            malePersons.add(person);
         }
      }
      return malePersons;
   }
}

// 女性條件
public class FemaleCriteria implements Criteria {
   @Override
   public List<Person> filter(List<Person> persons) {
      List<Person> femalePersons = new ArrayList<Person>(); 
      for (Person person : persons) {
         if(person.getGender().equalsIgnoreCase("FEMALE")){
            femalePersons.add(person);
         }
      }
      return femalePersons;
   }
}

// 單身條件
public class SingleCriteria implements Criteria {
   @Override
   public List<Person> filter(List<Person> persons) {
      List<Person> singlePersons = new ArrayList<Person>(); 
      for (Person person : persons) {
         if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){
            singlePersons.add(person);
         }
      }
      return singlePersons;
   }
}

// 與條件
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> filter(List<Person> persons) {
      List<Person> firstCriteriaPersons = criteria.filter(persons);     
      return otherCriteria.filter(firstCriteriaPersons);
   }
}

// 或條件
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> filter(List<Person> persons) {
      List<Person> firstCriteriaItems = criteria.filter(persons);
      List<Person> otherCriteriaItems = otherCriteria.filter(persons);
 
      for (Person person : otherCriteriaItems) {
         if(!firstCriteriaItems.contains(person)){
           firstCriteriaItems.add(person);
         }
      }  
      return firstCriteriaItems;
   }
}

// 使用示例
public class Demo {
   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 MaleCriteria();
      Criteria female = new FemaleCriteria();
      Criteria single = new SingleCriteria();
      Criteria singleMale = new AndCriteria(single, male);
      Criteria singleOrFemale = new OrCriteria(single, female);
 
      System.out.println("Males: ");
      printPersons(male.filter(persons));
 
      System.out.println("Females: ");
      printPersons(female.filter(persons));
 
      System.out.println("Single Males: ");
      printPersons(singleMale.filter(persons));
 
      System.out.println("Single Or Females: ");
      printPersons(singleOrFemale.filter(persons));
   }
 
   public static void printPersons(List<Person> persons){
      for (Person person : persons) {
         System.out.println(person.toString());
      }
   }      
}