过滤器模式

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。

示例演示：

1. 我们创建一个people实体

   package test.filter;
   
   import lombok.Data;
   
   @Data
   public class People {
   
       private Integer id;
       private String name;
   
       public People(Integer id, String name) {
           this.id = id;
           this.name = name;
       }
   }

2. 创建一个peopleId的接口，用于通过id对people分组

   package test.filter;
   
   import java.util.List;
   
   public interface PeopleId {
       public List<People> group(List<People> peoples);
   }

3. 接下来我们按照奇偶对id进行分类，我们创建两个实现类分班对group进行实现

   package test.filter;
   
   import java.util.ArrayList;
   import java.util.List;
   
   public class OddPeople implements PeopleId {
       @Override
       public List<People> group(List<People> peoples) {
           List<People> oddPeoples = new ArrayList<>();
           for (People people : peoples) {
               if (people.getId() % 2 != 0) {
                   oddPeoples.add(people);
               }
           }
           return oddPeoples;
       }
   }

   package test.filter;
   
   import java.util.ArrayList;
   import java.util.List;
   
   public class EvenPeople implements PeopleId {
       @Override
       public List<People> group(List<People> peoples) {
           List<People> evenPeoples = new ArrayList<>();
           for (People people : peoples) {
               if (people.getId() % 2 == 0) {
                   evenPeoples.add(people);
               }
           }
           return evenPeoples;
       }
   }

4. 完成上述步骤，我们就可以开始演示了

   package test.filter;
   
   import java.util.ArrayList;
   import java.util.List;
   
   public class FilterDemo {
       public static void main(String[] args) {
           List<People> peoples = new ArrayList<>();
   
           peoples.add(new People(1,"1"));
           peoples.add(new People(2,"2"));
           peoples.add(new People(3,"3"));
           peoples.add(new People(4,"4"));
           peoples.add(new People(5,"5"));
           peoples.add(new People(6,"6"));
           peoples.add(new People(7,"7"));
           peoples.add(new People(8,"8"));
           peoples.add(new People(9,"9"));
           peoples.add(new People(10,"10"));
   
           PeopleId oddPeople = new OddPeople();
           System.out.println(oddPeople.group(peoples).toString());
   
           PeopleId evenPeople = new EvenPeople();
           System.out.println(evenPeople.group(peoples).toString());
   
       }
   }

   运行结果：

   [People(id=1, name=1), People(id=3, name=3), People(id=5, name=5), People(id=7, name=7), People(id=9, name=9)]
   [People(id=2, name=2), People(id=4, name=4), People(id=6, name=6), People(id=8, name=8), People(id=10, name=10)]

   说明：

   过滤器模式就是我们对一组对象进行过滤，java8提供了里面就提供了很多方法来过滤数据，比如刚才的按照奇偶分类我们就可以直接使用java8提供的方法：

   Map<Integer, List<People>> groupList = peoples.stream().collect(Collectors.groupingBy(c -> c.getId()%2));