4、过滤器模式

以不同条件组合过滤人群为例。

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• 1、创建人群类：

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;
    }
}

• 2、创建标准接口：

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

• 3、创建实现了 Criteria 接口的实体类：

public class CriteriaMale implements Criteria{
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> malePersons = persons.stream().filter((item) -> {
            return item.getGender().equalsIgnoreCase("male");
        }).collect(Collectors.toList());
        return malePersons;
    }
}
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public class CriteriaFemale implements Criteria{
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> malePersons = persons.stream().filter((item) -> {
            return item.getGender().equalsIgnoreCase("female");
        }).collect(Collectors.toList());
        return malePersons;
    }
}
--------------------------------------------------------------------------
public class CriteriaSingle implements Criteria{
    @Override
    public List<Person> meetCriteria(List<Person> persons) {
        List<Person> malePersons = persons.stream().filter((item) -> {
            return item.getMaritalStatus().equalsIgnoreCase("single");
        }).collect(Collectors.toList());
        return malePersons;
    }
}
--------------------------------------------------------------------------
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> firstPersons = criteria.meetCriteria(persons);
        List<Person> resultPersons = otherCriteria.meetCriteria(firstPersons);
        return resultPersons;
    }
}
--------------------------------------------------------------------------
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> firstPersons = criteria.meetCriteria(persons);
        List<Person> otherPersons = otherCriteria.meetCriteria(persons);
        otherPersons.stream().forEach(item -> {
            if (!firstPersons.contains(item)){
                firstPersons.add(item);
            }
        });
        return firstPersons;
    }
}

• 4、使用不同的标准（Criteria）和它们的结合来过滤 Person 对象的列表：

public class CriteriaPatternDemo {
    public static void main(String[] args) {
        List<Person> persons = new ArrayList<Person>() {{
            add(new Person("Robert", "Male", "Single"));
            add(new Person("John", "Male", "Married"));
            add(new Person("Laura", "Female", "Married"));
            add(new Person("Diana", "Female", "Single"));
            add(new Person("Mike", "Male", "Single"));
            add(new Person("Bobby", "Male", "Single"));
        }};

        Criteria male = new CriteriaMale();
        Criteria female = new CriteriaFemale();
        Criteria single = new CriteriaSingle();
        Criteria singleAndMale = 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 And Males: ");
        printPersons(singleAndMale.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()
                    +" ]");
        }
    }
}

• 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 And 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 ]