设计模式--过滤器模式（标准模式）

简介

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。
优点：简单，解耦，使用方便。
使用场景：需要进行筛选时。

角色

过滤器模式包含如下角色：
　　(1) AbstractFilter（抽象过滤器角色）：定义过滤的方法。
　　(2) ConcreteFilter（具体滤器角色）：实现过滤的方法，对目标对象集合进行逻辑过滤，最后再返回一个过滤后的集合。
　　(3) Subject（被过滤角色）：目标角色，源数据，具体过滤器会对其进行逻辑处理。

简单示例

1.创建Subject（被过滤角色）

public class Student {
    private String name;
    private String gender;
    private String grade;
//getter setter .....
｝

2.创建 AbstractFilter（抽象过滤器角色）

public interface Filter {
    public List<Student> doFilt(List<Student> students);
}

3.创建ConcreteFilter（具体滤器角色）

public class Boy implements Filter {
    @Override
    public List<Student> doFilt(List<Student> students) {
        List<Student> students1 = new ArrayList<>();
        for (Student student: students) {
            if (student.getGender().equals("boy")){
                students1.add(student);
            }
        }
        return students1;
    }
}

public class Girl implements Filter{
    @Override
    public List<Student> doFilt(List<Student> students) {
        List<Student> students1 = new ArrayList<>();
        for (Student student: students) {
            if (student.getGender().equals("girl")){
                students1.add(student);
            }
        }
        return students1;
    }
}

public class GradeOne implements Filter {
    @Override
    public List<Student> doFilt(List<Student> students) {
        List<Student> students1 = new ArrayList<>();
        for (Student student: students) {
            if (student.getGrade().equals("one")){
                students1.add(student);
            }
        }
        return students1;
    }
}

public class GradeTwo implements Filter {
    @Override
    public List<Student> doFilt(List<Student> students) {
        List<Student> students1 = new ArrayList<>();
        for (Student student: students) {
            if (student.getGrade().equals("two")){
                students1.add(student);
            }
        }
        return students1;
    }
}

public class And implements Filter{
    private Filter filter1;
    private Filter filter2;

    public And(Filter filter1, Filter filter2) {
        this.filter1 = filter1;
        this.filter2 = filter2;
    }

    @Override
    public List<Student> doFilt(List<Student> students) {
        List<Student> students2 = filter1.doFilt(students);
        return filter2.doFilt(students2);
    }
}

public class Or implements Filter {
    private Filter filter1;
    private Filter filter2;
    public Or(Filter filter1,Filter filter2) {
        this.filter1 = filter1;
        this.filter2 = filter2;
    }
    @Override
    public List<Student> doFilt(List<Student> students) {
        List<Student> students1 = filter1.doFilt(students);
        List<Student> students2 = filter2.doFilt(students);
        for(Student student : students2) {
            if(!students1.contains(student)) {
                students1.add(student);
            }
        }
        return students1;
    }
}

4.Main验证

public class FilterMain extends Boy {
    public static void main(String[] args) {
        List<Student> students = new ArrayList<Student>();
        students.add(new Student("hello1","boy","one"));
        students.add(new Student("hello2","girl","two"));
        students.add(new Student("hello3","boy","two"));
        students.add(new Student("hello4","girl","one"));
        students.add(new Student("hello5","girl","one"));
        students.add(new Student("hello6","boy","two"));

        Filter boy = new Boy();
        System.out.println("boy list is : " +  boy.doFilt(students));
        Filter girl = new Girl();
        System.out.println("girl list is : " +  girl.doFilt(students));

        Filter one = new GradeOne();
        System.out.println("GradeOne list is : " +  one.doFilt(students));
        Filter two = new GradeTwo();
        System.out.println("GradeTwo list is : " +  two.doFilt(students));

        Filter oneBoy = new And(one,boy);
        System.out.println("GradeOne Boy list is : " + oneBoy.doFilt(students));

        Filter twoGirl = new And(two,girl);
        System.out.println("GradeTwo Girl list is : " + twoGirl.doFilt(students));

        Filter grilOrOne = new Or(one,girl);
        System.out.println("GradeOne or girl list is :" + grilOrOne.doFilt(students));
    }
}

boy list is : [Student{name='hello1', gender='boy', grade='one'}, Student{name='hello3', gender='boy', grade='two'}, Student{name='hello6', gender='boy', grade='two'}]
girl list is : [Student{name='hello2', gender='girl', grade='two'}, Student{name='hello4', gender='girl', grade='one'}, Student{name='hello5', gender='girl', grade='one'}]
GradeOne list is : [Student{name='hello1', gender='boy', grade='one'}, Student{name='hello4', gender='girl', grade='one'}, Student{name='hello5', gender='girl', grade='one'}]
GradeTwo list is : [Student{name='hello2', gender='girl', grade='two'}, Student{name='hello3', gender='boy', grade='two'}, Student{name='hello6', gender='boy', grade='two'}]
GradeOne Boy list is : [Student{name='hello1', gender='boy', grade='one'}]
GradeTwo Girl list is : [Student{name='hello2', gender='girl', grade='two'}]
GradeOne or girl list is :[Student{name='hello1', gender='boy', grade='one'}, Student{name='hello4', gender='girl', grade='one'}, Student{name='hello5', gender='girl', grade='one'}, Student{name='hello2', gender='girl', grade='two'}]