过滤器模式

小灰灰 2020-06-13 05:51 746阅读 0赞

### 介绍 ###

过滤器模式（Filter Pattern）或标准模式（Criteria Pattern）是一种设计模式，这种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。这种类型的设计模式属于结构型模式，它结合多个标准来获得单一标准。

### 实现 ###

我们将创建一个 *Person* 对象、*Criteria* 接口和实现了该接口的实体类，来过滤 *Person* 对象的列表。*CriteriaPatternDemo*，我们的演示类使用 *Criteria* 对象，基于各种标准和它们的结合来过滤 *Person* 对象的列表。  
![过滤器模式][format_png]

#### 步骤 1 ####

创建一个类，在该类上应用标准。

*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;
        }
    }

#### 步骤 2 ####

为标准（Criteria）创建一个接口。

*Criteria.java*

public interface Criteria {
    
        List<Person> meetCriteria(List<Person> persons);
    
    }

#### 步骤 3 ####

创建实现了 *Criteria* 接口的实体类。

*CriteriaMale.java*

public class CriteriaMale implements Criteria {
    
        @Override
        public List<Person> meetCriteria(List<Person> persons) {
            List<Person> malePersons = new ArrayList<>();
    
            for (Person person : persons) {
                if (person.getGender().equalsIgnoreCase("Male")) {
                    malePersons.add(person);
                }
            }
    
            return malePersons;
        }
        
    }

*CriteriaFemale.java*

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*

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*

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> list = criteria.meetCriteria(persons);
            return otherCriteria.meetCriteria(list);
        }
    
    }

*OrCriteria.java*

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> first = criteria.meetCriteria(persons);
            List<Person> other = otherCriteria.meetCriteria(persons);
    
            for (Person person : other) {
                if (!first.contains(person)) {
                    first.add(person);
                }
            }
    
            return first;
        }
    
    }

#### 步骤4 ####

使用不同的标准（Criteria）和它们的结合来过滤 *Person* 对象的列表。

*CriteriaPatternDemo.java*

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()
                        +" ]");
            }
        }
    
    }

#### 步骤 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 ]

[format_png]: /images/1592027481191.jpg