1、模式简介
过滤器模式(Filter)也叫标准模式(Criteria),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。
2、实例
这个实例的需求如下:
Person类有三个属性:姓名(Name)、性别(Gender)和婚姻情况(Marital),我们的系统中的一些功能需要对这些属性进行筛选,比如:
- 得到所有的男性;
- 得到所有的女性;
- 得到所有还单身的人;
- 得到所有已婚的人。
系统还希望能够将这些条件组合起来进行筛选,比如:
- 得到所有已婚男性;
- 得到所有单身女性;
- 得到所有已婚的人或女性;
分析:
要解决这个问题,我们可以使用过滤器模式。
代码:
Person类中的代码:
public class Person { private String name; // 姓名 private String gender; // 性别 private String marital; // 婚姻情况 public Person(String name, String gender, String marital) { this.name = name; this.gender = gender; this.marital = marital; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getGender() { return gender; } public void setGender(String gender) { this.gender = gender; } public String getMarital() { return marital; } public void setMarital(String marital) { this.marital = marital; } @Override public String toString() { return "Person [name=" + name + ",gender=" + gender + ", marital=" + marital + "]"; } }
Filter接口中的代码:
public interface Filter { // 根据传过来的Person列表,根据一定的条件过滤,得到目标集合 List<Person> filter(List<Person> persons); }
MaleFilter类中的代码:
public class MaleFilter implements Filter { @Override public List<Person> filter(List<Person> persons) { List<Person> result = new ArrayList<>(); for (Person person : persons) { if ("MALE".equalsIgnoreCase(person.getGender())) { result.add(person); } } return result; } }
处理“并且”逻辑的过滤器类FilterAnd类中的代码:
public class FilterAnd implements Filter { private Filter filter; private Filter otherFilter; public FilterAnd(Filter filter, Filter otherFilter) { this.filter = filter; this.otherFilter = otherFilter; } @Override public List<Person> filter(List<Person> persons) { List<Person> tmpList = filter.filter(persons); return otherFilter.filter(tmpList); } }
处理“或者”逻辑的过滤器类FilterOr类中的代码:
public class FilterOr implements Filter { private Filter filter; private Filter otherFilter; public FilterOr(Filter filter, Filter otherFilter) { this.filter = filter; this.otherFilter = otherFilter; } @Override public List<Person> filter(List<Person> persons) { List<Person> tmpList1 = filter.filter(persons); List<Person> tmpList2 = otherFilter.filter(persons); for (Person person : tmpList2) { if (!tmpList1.contains(person)) { tmpList1.add(person); } } return tmpList1; } }
测试类Test中的代码:
public class Test { public static void main(String[] args) { // 初始化数据 List<Person> persons = new ArrayList<>(); persons.add(new Person("霍一", "FEMALE", "MARRIED")); persons.add(new Person("邓二", "MALE", "MARRIED")); persons.add(new Person("张三", "MALE", "SINGLE")); persons.add(new Person("李四", "FEMALE", "MARRIED")); persons.add(new Person("王五", "MALE", "SINGLE")); persons.add(new Person("赵六", "FEMALE", "SINGLE")); persons.add(new Person("孙七", "MALE", "SINGLE")); persons.add(new Person("罗八", "MALE", "MARRIED")); persons.add(new Person("刘九", "FEMALE", "SINGLE")); persons.add(new Person("史十", "FEMALE", "SINGLE")); // 打印出所有男性的信息 System.out.println("---------------------所有男性---------------------"); List<Person> maleList = new MaleFilter().filter(persons); printList(maleList); // 打印出所有单身的信息 System.out.println("---------------------所有单身---------------------"); List<Person> singleList = new SingleFilter().filter(persons); printList(singleList); // 打印出所有已婚女性的信息 System.out.println("--------------------所有已婚女性-------------------"); List<Person> marriedFemaleList = new FilterAnd(new MarriedFilter(), new FemaleFilter()).filter(persons); printList(marriedFemaleList); // 打印出所有单身或女性的信息 System.out.println("-------------------所有单身或女性------------------"); List<Person> singleOrFemaleList = new FilterOr(new SingleFilter(), new FemaleFilter()).filter(persons); printList(singleOrFemaleList); } // 打印列表中的数据信息 private static void printList(List<Person> list) { for (Person person : list) { System.out.println(person.toString()); } } }
测试代码如下图所示:
最后贴出过滤器模式的GitHub代码:【GitHub - Filter】。