规则引擎之EasyRules

什么是EasyRules

首先EasyRule是一个规则引擎.这个名字由来是受到了Martin Fowler 的文章 Should I use a Rules Engine

You can build a simple rules engine yourself. All you need is to create a bunch of objects with conditions and actions, store them in a collection, and run through them to evaluate the conditions and execute the actions.

框架特点

轻量级类库和容易上手
基于POJO的开发与注解的编程模型
方便且适用于java的抽象的业务模型规则
支持从简单的规则创建组合规则

Useful abstractions to define business rules and apply them easily with Java
The ability to create composite rules from primitive ones

实践-FizzBuzz

循环打印 1 到 100，但如果是 5 的倍數就印 fizz，如果是 7 的倍數就印 buzz，如果同時是 5 和 7 的倍數就印 fizzzuzz,否则打印数字本身

不使用规则引擎

@Test
public void fizzbuzz() {
    for(int i = 1; i <= 100; i++) {
      if (((i % 5) == 0) && ((i % 7) == 0))
        System.out.print("fizzbuzz");
      else if ((i % 5) == 0) System.out.print("fizz");
      else if ((i % 7) == 0) System.out.print("buzz");
      else System.out.print(i);
      System.out.println();
    }
    System.out.println();
  }

使用Easy Rule

定义FizzRule

检查输入是否是fizz

@Rule
public class FizzRule {

    private int input;

    @Condition
    public boolean isFizz() {
        return input % 5 == 0;
    }

    @Action
    public void printFizz() {
        System.out.print("fizz");
    }

    public void setInput(int input) {
        this.input = input;
    }

    @Priority
    public int getPriority() {
        return 1;
    }
}

BuzzRule

检查输入是否是buzz

@Rule
public class BuzzRule {

    private int input;

    @Condition
    public boolean isBuzz() {
        return input % 7 == 0;
    }

    @Action
    public void printBuzz() {
        System.out.print("buzz");
    }

    public void setInput(int input) {
        this.input = input;
    }

    @Priority
    public int getPriority() {
        return 2;
    }
}

FizzBuzzRule

检查输入是否是fizzbuzz，这是一个组合规则，它由FizzRule和BuzzRule组成

public class FizzBuzzRule extends CompositeRule {

    public FizzBuzzRule(Object... rules) {
        for (Object rule : rules) {
            addRule(rule);
        }
    }

    @Override
    public int getPriority() {
        return 0;
    }
}

NonFizzBuzzRule

@Rule
public class NonFizzBuzzRule {

    private int input;

    @Condition
    public boolean isNotFizzNorBuzz() {
        // can return true here
        return input % 5 != 0 || input % 7 != 0;
    }

    @Action
    public void printInput() {
        System.out.print(input);
    }

    public void setInput(int input) {
        this.input = input;
    }

    @Priority
    public int getPriority() {
        return 3;
    }
}

执行

public class FizzBuzzWithEasyRules {

    public static void main(String[] args) {

        // create rules engine
        RulesEngine fizzBuzzEngine =
         RulesEngineBuilder.aNewRulesEngine()
                .withSkipOnFirstAppliedRule(true) // 如果第一个规则满足条件，后面的规则将不再执行
                .withSilentMode(true)
                .build();

        // create rules
        FizzRule fizzRule = new FizzRule();
        BuzzRule buzzRule = new BuzzRule();
        FizzBuzzRule fizzBuzzRule
            = new FizzBuzzRule(fizzRule, buzzRule);
        NonFizzBuzzRule nonFizzBuzzRule = new NonFizzBuzzRule();

        // register rules
        fizzBuzzEngine.registerRule(fizzRule);
        fizzBuzzEngine.registerRule(buzzRule);
        fizzBuzzEngine.registerRule(fizzBuzzRule);
        fizzBuzzEngine.registerRule(nonFizzBuzzRule);

        // fire rules
        for (int i = 1; i <= 100; i++) {
            fizzRule.setInput(i);
            buzzRule.setInput(i);
            nonFizzBuzzRule.setInput(i);
            fizzBuzzEngine.fireRules();
            System.out.println();
        }
    }
}