Design and Implementation of a Java Rule Engine with Short‑Circuit Evaluation

The author received a requirement to extend an existing trial‑user application rule set, which originally consisted of a long chain of if‑else statements that were hard to maintain and lacked short‑circuit behavior.

Recognizing that the business logic is fundamentally based on AND/OR relationships, the author decided to redesign the rule processing component to support short‑circuit evaluation, improving both performance and maintainability.

Rule Engine Design (V1)

The design introduces a RuleDto data transfer object, a BaseRule interface, an abstract AbstractRule class that handles generic conversion and execution, and concrete rule classes such as AddressRule and NationalityRule. Constants for matching criteria are defined in RuleConstant.

// 业务数据
@Data
public class RuleDto {
  private String address;
  private int age;
}

// 规则抽象
public interface BaseRule {
    boolean execute(RuleDto dto);
}

// 规则模板
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; }
}

// 具体规则‑ 例子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;
    }
}

// 具体规则‑ 例子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 nr = (NationalityRuleDto) t;
        if (nr.getNationality().startsWith(MATCH_NATIONALITY_START)) {
            return true;
        }
        return false;
    }
}

// 常量定义
public class RuleConstant {
    public static final String MATCH_ADDRESS_START = "北京";
    public static final String MATCH_NATIONALITY_START = "中国";
}

Rule Service Construction

The RuleService maintains a map of rule lists keyed by logical operators (AND = 1, OR = 0). It provides fluent and() and or() methods to register rule groups and an execute() method that iterates over the map, applying short‑circuit logic for each operator.

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:
                    System.out.println("execute key = " + 1);
                    if (!and(dto, ruleList)) return false;
                    break;
                case OR:
                    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) {
            if (!rule.execute(dto)) return false;
        }
        return true;
    }
    private boolean or(RuleDto dto, List<BaseRule> ruleList) {
        for (BaseRule rule : ruleList) {
            if (rule.execute(dto)) return true;
        }
        return false;
    }
}

Engine Invocation Example

A JUnit test demonstrates creating concrete rule instances, populating a RuleDto, and chaining and() and or() calls before executing the rule service.

public class RuleServiceTest {
    @org.junit.Test
    public void execute() {
        AgeRule ageRule = new AgeRule();
        NameRule nameRule = new NameRule();
        NationalityRule nationalityRule = new NationalityRule();
        AddressRule addressRule = new AddressRule();
        SubjectRule subjectRule = new SubjectRule();
        RuleDto dto = new RuleDto();
        dto.setAge(5);
        dto.setName("张三");
        dto.setAddress("北京");
        dto.setSubject("数学");
        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 of Advantages and Disadvantages

Advantages: the architecture is simple, each rule is independent, and the separation of rule, data, and executor makes the caller code clean; the abstract convert method allows rule‑specific data transformation.

Disadvantages: all rules share the same DTO, creating hidden data dependencies; modifying the DTO directly can lead to coupling, so it is recommended to construct dedicated data objects for each rule.