6.10. Filter mode

Filter pattern (Filter Pattern) or standard pattern (Criteria Pattern) is a design pattern that allows developers to filter a set of objects using different standards and connect them in a decoupled manner through logical operations. This type of design pattern belongs to structural pattern, which combines multiple standards to obtain a single standard.

6.10.1. Realize ¶

We will create a Person Object, Criteria Interface and the entity class that implements the interface, to filter Person A list of objects. CriteriaPatternDemo Class usage Criteria Object that is filtered based on various standards and their combination Person A list of objects.

过滤器模式的 UML 图

6.10.2. Step 1 ¶

Create a class and apply standards to it.

Person.java ¶

publicclassPerson{privateStringname;privateStringgender;privateStringmaritalStatus;publicPerson(Stringname,Stringgender,StringmaritalStatus){this.name=name;this.gender=gender;this.maritalStatus=maritalStatus;}publicStringgetName(){returnname;}publicStringgetGender(){returngender;}publicStringgetMaritalStatus(){returnmaritalStatus;}}

6.10.3. Step 2 ¶

Create an interface for the standard (Criteria).

Criteria.java ¶

importjava.util.List;publicinterfaceCriteria{publicList<Person>meetCriteria(List<Person>persons);}

6.10.4. Step 3 ¶

Create and implement the Criteria The entity class of the interface.

CriteriaMale.java ¶

importjava.util.ArrayList;importjava.util.List;publicclassCriteriaMaleimplementsCriteria{@OverridepublicList<Person>meetCriteria(List<Person>persons){List<Person>malePersons=newArrayList<Person>();for(Personperson:persons){if(person.getGender().equalsIgnoreCase("MALE")){malePersons.add(person);}}returnmalePersons;}}

CriteriaFemale.java ¶

importjava.util.ArrayList;importjava.util.List;publicclassCriteriaFemaleimplementsCriteria{@OverridepublicList<Person>meetCriteria(List<Person>persons){List<Person>femalePersons=newArrayList<Person>();for(Personperson:persons){if(person.getGender().equalsIgnoreCase("FEMALE")){femalePersons.add(person);}}returnfemalePersons;}}

CriteriaSingle.java ¶

importjava.util.ArrayList;importjava.util.List;publicclassCriteriaSingleimplementsCriteria{@OverridepublicList<Person>meetCriteria(List<Person>persons){List<Person>singlePersons=newArrayList<Person>();for(Personperson:persons){if(person.getMaritalStatus().equalsIgnoreCase("SINGLE")){singlePersons.add(person);}}returnsinglePersons;}}

AndCriteria.java ¶

importjava.util.List;publicclassAndCriteriaimplementsCriteria{privateCriteriacriteria;privateCriteriaotherCriteria;publicAndCriteria(Criteriacriteria,CriteriaotherCriteria){this.criteria=criteria;this.otherCriteria=otherCriteria;}@OverridepublicList<Person>meetCriteria(List<Person>persons){List<Person>firstCriteriaPersons=criteria.meetCriteria(persons);returnotherCriteria.meetCriteria(firstCriteriaPersons);}}

OrCriteria.java ¶

importjava.util.List;publicclassOrCriteriaimplementsCriteria{privateCriteriacriteria;privateCriteriaotherCriteria;publicOrCriteria(Criteriacriteria,CriteriaotherCriteria){this.criteria=criteria;this.otherCriteria=otherCriteria;}@OverridepublicList<Person>meetCriteria(List<Person>persons){List<Person>firstCriteriaItems=criteria.meetCriteria(persons);List<Person>otherCriteriaItems=otherCriteria.meetCriteria(persons);for(Personperson:otherCriteriaItems){if(!firstCriteriaItems.contains(person)){firstCriteriaItems.add(person);}}returnfirstCriteriaItems;}}

6.10.5. Step 4 ¶

Use different standards (Criteria) and their combination to filter Person A list of objects.

CriteriaPatternDemo.java ¶

importjava.util.ArrayList;importjava.util.List;publicclassCriteriaPatternDemo{publicstaticvoidmain(String[]args){List<Person>persons=newArrayList<Person>();persons.add(newPerson("Robert","Male","Single"));persons.add(newPerson("John","Male","Married"));persons.add(newPerson("Laura","Female","Married"));persons.add(newPerson("Diana","Female","Single"));persons.add(newPerson("Mike","Male","Single"));persons.add(newPerson("Bobby","Male","Single"));Criteriamale=newCriteriaMale();Criteriafemale=newCriteriaFemale();Criteriasingle=newCriteriaSingle();CriteriasingleMale=newAndCriteria(single,male);CriteriasingleOrFemale=newOrCriteria(single,female);System.out.println("Males:");printPersons(male.meetCriteria(persons));System.out.println("\\nFemales:");printPersons(female.meetCriteria(persons));System.out.println("\\nSingle
Males:");printPersons(singleMale.meetCriteria(persons));System.out.println("\\nSingle
Or
Females:");printPersons(singleOrFemale.meetCriteria(persons));}publicstaticvoidprintPersons(List<Person>persons){for(Personperson:persons){System.out.println("Person
: [ Name :"+person.getName()+", Gender :"+person.getGender()+", Marital
Status :"+person.getMaritalStatus()+"]");}}}

6.10.6. Step 5 ¶

Execute the program and output the result:

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 ]
Person : [ Name : Laura, Gender : Female, Marital Status : Married ]