Business scenario

Recently, I received a small demand in the company, which needs to expand the existing trial user application rules. Our scenario is roughly as follows:

if (Overseas users) {
 return false;
}

if (Billing user) {
  return false;
}

if (Unpaid user && No longer service period) {
  return false
}

if (Transfer to introduce users || Paying user || Push user) {
  return true;
}

According to the above conditions, we can conclude that:

• Our main process is mainly based on the relationship between and or.

• If there is a mismatch, in fact, our subsequent processes do not need to be executed, but need to have a short-circuit function.

• For the current situation, if I change it on the original basis, I just need to pay a little attention to solve the problem that the demand is not very big, but the maintainability is very poor.

After weighing later, I decided to refactor this part.

Rule executor

To meet this demand, I first sorted out the general design of our rule executor, and then I designed a V1 version to share with you. If you also have such a case, you can share a message with me. The following part is mainly about the design and implementation process and code

Design rule of executor

Abstraction of rules and implementation of rules

//Business data
@Data
public class RuleDto {
  private String address;
 private int age;
}

//Rule abstraction
public interface BaseRule {

    boolean execute(RuleDto dto);
}

//Rule Template
public abstract class AbstractRule implements BaseRule {

    protected <T> T convert(RuleDto dto) {
        return (T) dto;
    }

    @Override
    public boolean execute(RuleDto dto) {
        return executeRule(convert(dto));
    }
  
    protected <T> boolean executeRule(T t) {
        return true;
    }
}

//Specific rules - Example 1
public class AddressRule extends AbstractRule {

    @Override
    public boolean execute(RuleDto dto) {
        System.out.println("AddressRule invoke!");
        if (dto.getAddress().startsWith(MATCH_ADDRESS_START)) {
            return true;
        }
        return false;
    }
}

//Specific rules - Example 2
public class NationalityRule extends AbstractRule {

    @Override
    protected <T> T convert(RuleDto dto) {
        NationalityRuleDto nationalityRuleDto = new NationalityRuleDto();
        if (dto.getAddress().startsWith(MATCH_ADDRESS_START)) {
            nationalityRuleDto.setNationality(MATCH_NATIONALITY_START);
        }
        return (T) nationalityRuleDto;
    }


    @Override
    protected <T> boolean executeRule(T t) {
        System.out.println("NationalityRule invoke!");
        NationalityRuleDto nationalityRuleDto = (NationalityRuleDto) t;
        if (nationalityRuleDto.getNationality().startsWith(MATCH_NATIONALITY_START)) {
            return true;
        }
        return false;
    }
}

//Constant definition
public class RuleConstant {
    public static final String MATCH_ADDRESS_START= "Beijing";
    public static final String MATCH_NATIONALITY_START= "China";
}

Actuator construction

public class RuleService {

    private Map<Integer, List<BaseRule>> hashMap = new HashMap<>();
    private static final int AND = 1;
    private static final int OR = 0;

    public static RuleService create() {
        return new RuleService();
    }


    public RuleService and(List<BaseRule> ruleList) {
        hashMap.put(AND, ruleList);
        return this;
    }

    public RuleService or(List<BaseRule> ruleList) {
        hashMap.put(OR, ruleList);
        return this;
    }

    public boolean execute(RuleDto dto) {
        for (Map.Entry<Integer, List<BaseRule>> item : hashMap.entrySet()) {
            List<BaseRule> ruleList = item.getValue();
            switch (item.getKey()) {
                case AND:
                    //If it is a ， and ， relationship, execute synchronously
                    System.out.println("execute key = " + 1);
                    if (!and(dto, ruleList)) {
                        return false;
                    }
                    break;
                case OR:
                    //If it is an ， or ， relationship, execute in parallel
                    System.out.println("execute key = " + 0);
                    if (!or(dto, ruleList)) {
                        return false;
                    }
                    break;
                default:
                    break;
            }
        }
        return true;
    }

    private boolean and(RuleDto dto, List<BaseRule> ruleList) {
        for (BaseRule rule : ruleList) {
            boolean execute = rule.execute(dto);
            if (!execute) {
                //And relationship matching fails once, and false is returned
                return false;
            }
        }
        //And ， all relationships match successfully, and ， true is returned
        return true;
    }

    private boolean or(RuleDto dto, List<BaseRule> ruleList) {
        for (BaseRule rule : ruleList) {
            boolean execute = rule.execute(dto);
            if (execute) {
                //or ， returns ， true if the relationship matches one
                return true;
            }
        }
        //or ， false is returned if none of the relationships match
        return false;
    }
}

Call of actuator

public class RuleServiceTest {

    @org.junit.Test
    public void execute() {
        //Rule executor
        //Advantages: it is relatively simple. Each rule can be independent. The rule, data and actuator are separated, and the caller is relatively regular
        //Disadvantages: data depends on the common transmission object dto

        //1. Define init rule
        AgeRule ageRule = new AgeRule();
        NameRule nameRule = new NameRule();
        NationalityRule nationalityRule = new NationalityRule();
        AddressRule addressRule = new AddressRule();
        SubjectRule subjectRule = new SubjectRule();

        //2. Construct the required data # create # dto
        RuleDto dto = new RuleDto();
        dto.setAge(5);
        dto.setName("Zhang San");
        dto.setAddress("Beijing");
        dto.setSubject("mathematics");;

        //3. Build and execute # rule # execute through chain call
        boolean ruleResult = RuleService
                .create()
                .and(Arrays.asList(nationalityRule, nameRule, addressRule))
                .or(Arrays.asList(ageRule, subjectRule))
                .execute(dto);
        System.out.println("this student rule execute result :" + ruleResult);
    }
}

summary

Advantages and disadvantages of rule executors

advantage:

• It is relatively simple. Each rule can be independent. The rule, data and actuator are separated, and the caller is relatively regular;

• I define the convert method in the rule template class to convert parameters, which can provide expansion for the scene data required by specific rules.

Disadvantages:

• The upper and lower rule s are data dependent. If it is unreasonable to directly modify the public transmission object dto, it is recommended to build the data in advance.