结构型模式- 过滤器模式（过滤对象）
过滤器模式Filter pattern，标准模式Criteria Pattern
意图
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链接起来。
示例
创建一个Person对象，Criteria接口和具体类，实现该接口以过滤Person对象列表。CriteriaPatternDemo是一个演示类，使用Criteria对象基于各种标准及其组合过滤拥有Person对象的列表（List）。
UML类图
实现代码
- 创建Person，待过滤对象
// 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;
}
}
- 创建过滤接口Criteria
// Criteria.java
/**
* Filter person list using Criteria
*/
public interface Criteria {
public List<Person> meetCriteria(List<Person> persons);
}
- 创建实现接口Criteria的实体类FemaleCriteria, MaleCriteria, SingleCriteria, AndCriteria, OrCriteria，用于过滤Person列表，得到符合要求的Person 列表
// FemaleCriteria.java
public class FemaleCriteria implements Criteria {
@Override
public List<Person> meetCriteria(List<Person> persons) {
List<Person> femalePersons = new ArrayList<Person>();
for(Person person: persons) {
if(person.getGender().equalsIgnoreCase("FEMALE")) {
femalePersons.add(person);
}
}
return femalePersons;
}
}
// MaleCriteria.java
public class MaleCriteria implements Criteria {
@Override
public List<Person> meetCriteria(List<Person> persons) {
List<Person> malePersons = new ArrayList<Person>();
for(Person person: persons) {
if(person.getGender().equalsIgnoreCase("MALE")) {
malePersons.add(person);
}
}
return malePersons;
}
}
// SingleCriteria.java
public class SingleCriteria implements Criteria {
@Override
public List<Person> meetCriteria(List<Person> persons) {
List<Person> singlePersons = new ArrayList<Person>();
for(Person person: persons) {
if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")) {
singlePersons.add(person);
}
}
return singlePersons;
}
}
// AndCriteria.java
/**
* Filter Person list which meet criteria and otherCriteria
*/
public class AndCriteria implements Criteria {
protected Criteria criteria;
protected Criteria otherCriteria;
public AndCriteria(Criteria criteria, Criteria otherCriteria) {
this.criteria = criteria;
this.otherCriteria = otherCriteria;
}
@Override
public List<Person> meetCriteria(List<Person> persons) {
List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);
return otherCriteria.meetCriteria(firstCriteriaPersons);
}
}
// OrCriteria.java
/**
* filter Person list which meet criteria or otherCriteria
*/
public class OrCriteria implements Criteria {
protected Criteria criteria;
protected Criteria otherCriteria;
public OrCriteria(Criteria criteria, Criteria otherCriteria) {
this.criteria = criteria;
this.otherCriteria = otherCriteria;
}
@Override
public List<Person> meetCriteria(List<Person> persons) {
List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);
List<Person> otherCriterialPersons = criteria.meetCriteria(persons);
for(Person person: otherCriterialPersons)
{
if(!firstCriteriaPersons.contains(person))
{
firstCriteriaPersons.add(person);
}
}
return firstCriteriaPersons;
}
}
- 创建FilterPatternDemo类使用过滤模式，新建Person列表对象和具体的过滤对象，用过滤模式过滤Person列表得到期望的Person列表
// FilterPatternDemo.java
public class FilterPatternDemo {
public static void main(String[] args) {
List<Person> persons = new ArrayList<Person>();
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 MaleCriteria();
Criteria female = new FemaleCriteria();
Criteria single = new SingleCriteria();
Criteria singleMale = new AndCriteria(single, male);
Criteria singleOrFemal = new OrCriteria(single, female);
System.out.println("Males:");
printPersons(male.meetCriteria(persons));
System.out.println("Females:");
printPersons(female.meetCriteria(persons));
System.out.println("Single Males:");
printPersons(singleMale.meetCriteria(persons));
System.out.println("Single or Females:");
printPersons(singleOrFemal.meetCriteria(persons));
}
static void printPersons(List<Person> persons) {
for(Person person: persons) {
System.out.println("Person: [ Name: " + person.getName()
+ ", Gender:" + person.getGender()
+ ", Marital Status: "
+ person.getMaritalStatus() + "]");
}
}
}
运行结果
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]
