java - 用于评估 Java 对象上的逻辑表达式的库

Question

假设我有以下类(class):

class Person {
    int age;
    String city;
    Collection<Person> friends;
    Person spouse;
}

我需要一个库来评估逻辑表达式在给定的 Person 对象上是否为真。表达式看起来像这样:

((age>25 OR spouse.age>27) AND city=="New-York" AND size(friends)>100)

所以，要求是:

1. 能够使用基本的逻辑运算符
2. 访问给定对象的属性
3. 访问内部对象的属性
4. 使用简单的数学\类似 sql 的函数，例如 size、max、sum

建议？

Answer 1

你可以使用 ScriptEngine + 反射(reflection):

• 访问所有fields在您的对象中创建具有这些值的变量
• 评估表达式

这是一个输出的人为例子:

age = 35
city = "London"
age > 32 && city == "London" => true
age > 32 && city == "Paris" => false
age < 32 && city == "London" => false

如果你想处理非基本类型，比如集合，它可能会变得非常困惑。

public class Test1 {

    public static void main(String[] args) throws Exception{
        Person p = new Person();
        p.age = 35;
        p.city = "London";

        ScriptEngineManager factory = new ScriptEngineManager();
        ScriptEngine engine = factory.getEngineByName("JavaScript");

        Class<Person> c = Person.class;
        for (Field f : c.getDeclaredFields()) {
            Object o = f.get(p);
            String assignement = null;
            if (o instanceof String) {
                assignement = f.getName() + " = \"" + String.valueOf(o) + "\"";
            } else {
                assignement = f.getName() + " = " + String.valueOf(o);
            }
            engine.eval(assignement);
            System.out.println(assignement);
        }

        String condition = "age > 32 && city == \"London\"";
        System.out.println(condition + " => " + engine.eval(condition));

        condition = "age > 32 && city == \"Paris\"";
        System.out.println(condition + " => " + engine.eval(condition));

        condition = "age < 32 && city == \"London\"";
        System.out.println(condition + " => " + engine.eval(condition));
    }

    public static class Person {

        int age;
        String city;
    }
}