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    标题：Java过滤器模式(条件模式)

    过滤器模式或条件模式是一种设计模式，使开发人员可以使用不同的条件过滤一组对象，并通过逻辑操作以解耦方式将其链接。 这种类型的设计模式属于结构模式，因为该模式组合多个标准以获得单个标准。

    实现实现

    我们将创建一个Person对象，Criteria接口和具体类，实现这个接口来过滤Person对象的列表。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)。

    示例的结构图如下 -

    第1步

    创建要应用标准的类。

    Person.java

    1. public class Person {
    2.  
    3.    private String name;
    4.    private String gender;
    5.    private String maritalStatus;
    6.  
    7.    public Person(String name, String gender, String maritalStatus){
    8.       this.name = name;
    9.       this.gender = gender;
    10.       this.maritalStatus = maritalStatus;        
    11.    }
    12.  
    13.    public String getName() {
    14.       return name;
    15.    }
    16.    public String getGender() {
    17.       return gender;
    18.    }
    19.    public String getMaritalStatus() {
    20.       return maritalStatus;
    21.    }    
    22. }
    23. Java

    第2步

    创建Criteria的接口。

    Criteria.java

    1. import java.util.List;
    2.  
    3. public interface Criteria {
    4.    public List<Person> meetCriteria(List<Person> persons);
    5. }
    6. Java

    第3步

    创建实现Criteria接口的具体类。

    CriteriaMale.java

    1. import java.util.ArrayList;
    2. import java.util.List;
    3.  
    4. public class CriteriaMale implements Criteria {
    5.  
    6.    @Override
    7.    public List<Person> meetCriteria(List<Person> persons) {
    8.       List<Person> malePersons = new ArrayList<Person>(); 
    9.  
    10.       for (Person person : persons) {
    11.          if(person.getGender().equalsIgnoreCase("MALE")){
    12.             malePersons.add(person);
    13.          }
    14.       }
    15.       return malePersons;
    16.    }
    17. }
    18. Java

    CriteriaFemale.java

    1. import java.util.ArrayList;
    2. import java.util.List;
    3.  
    4. public class CriteriaFemale implements Criteria {
    5.  
    6.    @Override
    7.    public List<Person> meetCriteria(List<Person> persons) {
    8.       List<Person> femalePersons = new ArrayList<Person>(); 
    9.  
    10.       for (Person person : persons) {
    11.          if(person.getGender().equalsIgnoreCase("FEMALE")){
    12.             femalePersons.add(person);
    13.          }
    14.       }
    15.       return femalePersons;
    16.    }
    17. }
    18. Java

    CriteriaSingle.java

    1. import java.util.ArrayList;
    2. import java.util.List;
    3.  
    4. public class CriteriaSingle implements Criteria {
    5.  
    6.    @Override
    7.    public List<Person> meetCriteria(List<Person> persons) {
    8.       List<Person> singlePersons = new ArrayList<Person>(); 
    9.  
    10.       for (Person person : persons) {
    11.          if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){
    12.             singlePersons.add(person);
    13.          }
    14.       }
    15.       return singlePersons;
    16.    }
    17. }
    18. Java

    AndCriteria.java

    1. import java.util.List;
    2.  
    3. public class AndCriteria implements Criteria {
    4.  
    5.    private Criteria criteria;
    6.    private Criteria otherCriteria;
    7.  
    8.    public AndCriteria(Criteria criteria, Criteria otherCriteria) {
    9.       this.criteria = criteria;
    10.       this.otherCriteria = otherCriteria; 
    11.    }
    12.  
    13.    @Override
    14.    public List<Person> meetCriteria(List<Person> persons) {
    15.  
    16.       List<Person> firstCriteriaPersons = criteria.meetCriteria(persons);        
    17.       return otherCriteria.meetCriteria(firstCriteriaPersons);
    18.    }
    19. }
    20. Java

    OrCriteria.java

    1. import java.util.List;
    2.  
    3. public class OrCriteria implements Criteria {
    4.  
    5.    private Criteria criteria;
    6.    private Criteria otherCriteria;
    7.  
    8.    public OrCriteria(Criteria criteria, Criteria otherCriteria) {
    9.       this.criteria = criteria;
    10.       this.otherCriteria = otherCriteria; 
    11.    }
    12.  
    13.    @Override
    14.    public List<Person> meetCriteria(List<Person> persons) {
    15.       List<Person> firstCriteriaItems = criteria.meetCriteria(persons);
    16.       List<Person> otherCriteriaItems = otherCriteria.meetCriteria(persons);
    17.  
    18.       for (Person person : otherCriteriaItems) {
    19.          if(!firstCriteriaItems.contains(person)){
    20.             firstCriteriaItems.add(person);
    21.          }
    22.       }    
    23.       return firstCriteriaItems;
    24.    }
    25. }
    26. Java

    第4步

    使用不同的条件及其组合过滤掉人。

    CriteriaPatternDemo.java

    1. public class CriteriaPatternDemo {
    2.    public static void main(String[] args) {
    3.       List<Person> persons = new ArrayList<Person>();
    4.  
    5.       persons.add(new Person("Robert","Male", "Single"));
    6.       persons.add(new Person("John", "Male", "Married"));
    7.       persons.add(new Person("Laura", "Female", "Married"));
    8.       persons.add(new Person("Diana", "Female", "Single"));
    9.       persons.add(new Person("Mike", "Male", "Single"));
    10.       persons.add(new Person("Bobby", "Male", "Single"));
    11.  
    12.       Criteria male = new CriteriaMale();
    13.       Criteria female = new CriteriaFemale();
    14.       Criteria single = new CriteriaSingle();
    15.       Criteria singleMale = new AndCriteria(single, male);
    16.       Criteria singleOrFemale = new OrCriteria(single, female);
    17.  
    18.       System.out.println("Males: ");
    19.       printPersons(male.meetCriteria(persons));
    20.  
    21.       System.out.println("\nFemales: ");
    22.       printPersons(female.meetCriteria(persons));
    23.  
    24.       System.out.println("\nSingle Males: ");
    25.       printPersons(singleMale.meetCriteria(persons));
    26.  
    27.       System.out.println("\nSingle Or Females: ");
    28.       printPersons(singleOrFemale.meetCriteria(persons));
    29.    }
    30.  
    31.    public static void printPersons(List<Person> persons){
    32.  
    33.       for (Person person : persons) {
    34.          System.out.println("Person : [ Name : " + person.getName() + ", Gender : " + person.getGender() + ", Marital Status : " + person.getMaritalStatus() + " ]");
    35.       }
    36.    }      
    37. }
    38. Java

    第5步

    验证输出结果，执行上面的代码得到结果如下 -

    1. Males: 
    2. Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
    3. Person : [ Name : John, Gender : Male, Marital Status : Married ]
    4. Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
    5. Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]
    6.  
    7. Females: 
    8. Person : [ Name : Laura, Gender : Female, Marital Status : Married ]
    9. Person : [ Name : Diana, Gender : Female, Marital Status : Single ]
    10.  
    11. Single Males: 
    12. Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
    13. Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
    14. Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]
    15.  
    16. Single Or Females: 
    17. Person : [ Name : Robert, Gender : Male, Marital Status : Single ]
    18. Person : [ Name : Diana, Gender : Female, Marital Status : Single ]
    19. Person : [ Name : Mike, Gender : Male, Marital Status : Single ]
    20. Person : [ Name : Bobby, Gender : Male, Marital Status : Single ]
    21. Person : [ Name : Laura, Gender : Female, Marital Status : Married ]
    22. Java

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