代码详解设计模式--过滤器模式

深藏阁楼爱情的钟 2022-03-20 10:12 212阅读 0赞

# 过滤器模式 #

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。最常见的应用如MyBatis中。

![UML][]

// 实体
    @Data
    @AllArgsConstructor
    public class Person { 
       private String name;
       private String gender;
       private String maritalStatus;
    }
    
    // 条件接口
    public interface Criteria { 
       public List<Person> filter(List<Person> persons);
    }
    
    // 男性条件
    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;
       }
    }
    
    // 女性条件
    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;
       }
    }
    
    // 单身条件
    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;
       }
    }
    
    // 与条件
    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);
       }
    }
    
    // 或条件
    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());
          }
       }      
    }

[UML]: /images/20220320/a4d21f4902b040df8f42cd36bb165fc1.png