设计模式 过滤器模式

  • 设计模式 - 过滤器模式

    过滤器模式或称条件模式是一种设计模式,使开发人员可以使用不同的条件过滤一组对象,并通过逻辑操作以分离的方式链接它们。这种类型的设计模式属于结构模式,因为该模式组合了多个条件以获得单个条件。
  • 实例

    我们将创建一个Person对象,Criteria接口和实现此接口的具体类,以过滤Person对象的列表 。CriteriaPatternDemo,我们的演示类使用Criteria对象根据各种条件及其组合来过滤Person对象的List 。
    dp
    第1步 - 创建一个要在其上应用条件的类。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;
       }    
    }
    
    第2步 - 为条件创建一个接口。 Criteria.java
    
    import java.util.List;
    
    public interface Criteria {
       public List<Person> meetCriteria(List<Person> persons);
    }
    
    第3步 - 创建实现Criteria接口的具体类。CriteriaMale.java , CriteriaFemale.java , CriteriaSingle.java , AndCriteria.java, OrCriteria.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;
       }
    }
    
    
    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;
       }
    }
    
    
    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;
       }
    }
    
    
    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);
       }
    }
    
    
    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;
       }
    }
    
    步骤4 - 使用不同的条件及其组合来过滤人员。 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() + " ]");
          }
       }      
    }
    
    第5步 - 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 ]