设计模式 过滤器模式
发布日期:2021-06-30 17:39:21
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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。
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
import java.util.List; public interface Criteria { public ListmeetCriteria(List persons);}
步骤 3
创建实现了 Criteria 接口的实体类。
CriteriaMale.java
import java.util.ArrayList;import java.util.List; public class CriteriaMale implements Criteria { @Override public ListmeetCriteria(List persons) { List malePersons = new ArrayList (); for (Person person : persons) { if(person.getGender().equalsIgnoreCase("MALE")){ malePersons.add(person); } } return malePersons; }}
CriteriaFemale.java
import java.util.ArrayList;import java.util.List; public class CriteriaFemale implements Criteria { @Override public ListmeetCriteria(List persons) { List femalePersons = new ArrayList (); for (Person person : persons) { if(person.getGender().equalsIgnoreCase("FEMALE")){ femalePersons.add(person); } } return femalePersons; }}
CriteriaSingle.java
import java.util.ArrayList;import java.util.List; public class CriteriaSingle implements Criteria { @Override public ListmeetCriteria(List persons) { List singlePersons = new ArrayList (); for (Person person : persons) { if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){ singlePersons.add(person); } } return singlePersons; }}
AndCriteria.java
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 ListmeetCriteria(List persons) { List firstCriteriaPersons = criteria.meetCriteria(persons); return otherCriteria.meetCriteria(firstCriteriaPersons); }}
OrCriteria.java
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 ListmeetCriteria(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
import java.util.ArrayList; import java.util.List; public class CriteriaPatternDemo { public static void main(String[] args) { Listpersons = 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() +" ]"); } } }
步骤 5
执行程序,输出结果:
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 ]
总结
过滤模式的实现在java8里面有典型的应用方法就是分组操作,可以根据指定的指标进行分组筛选。
Map> groupMap = persons.stream().collect(Collectors.groupingBy(Person::getGender));groupMap.forEach((k, v) -> { System.out.println(k); v.forEach(System.out::println);});
得到的结果形式就是:
- k:是分组的指标,上面代码中的 gender
- v:是一个list的集合对象,就是 personList
可以参考:
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