Java-解析用户定义的函数

问题描述

我正在开发一个程序，我希望用户定义一个简单的函数，例如 randomInt(0,10)或者 randomString(10)而不是静态参数.解析和处理此类功能的最佳方法是什么?

I am working on a program, where I want users to define a simple functions like randomInt(0,10)or randomString(10)instead of static arguments. What is the best way to parse and process such functions ?

我还没有发现任何此类问题的示例，解析器不必具有超高效率，它不会经常被调用，但主要是我想着重于良好的代码可读性和可伸缩性.

I have not found any examples of such problem, the parser does not have to be ultra-efficient, it will not be called often, but mainly I want to focus on good code readability and scalability.

用户输入示例:

"This is user randomString(5) and he is randomInt(18,60) years old!"

预期输出:

"This is user phiob and he is 45 years old!"

"This is user sdfrt and he is 30 years old!"

推荐答案

一种选择是使用Spring SPEL.但这会迫使您稍微改变一下表达式并使用Spring库:

One option is to use Spring SPEL. But it forces you to change the expression a little and use Spring library:

表达式可以如下所示:

'This is user ' + randomString(5) + ' and he is ' + randomInt(18,60) + ' years old!'

或者这个:

This is user #{randomString(5)} and he is #{randomInt(18,60)} years old!

或者您可以通过自定义TemplateParserContext来实现自己的功能.

or you can implement your own by having a custom TemplateParserContext.

这是代码:

import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.spel.support.StandardEvaluationContext;

public class SomeTest {

        @Test
        public void test() {
            ExpressionParser parser = new SpelExpressionParser();

            Expression exp = parser.parseExpression(
                "This is user #{randomString(5)} and he is #{randomInt(18,60)} years old!",
                new TemplateParserContext() );

            //alternative
            //Expression exp = parser.parseExpression(
            //        "'This is user ' + randomString(5) + ' and he is ' + randomInt(18,60) + ' years old!'");
            //    String message = (String) exp.getValue( new StandardEvaluationContext(this) );


            String message = (String) exp.getValue( new StandardEvaluationContext(this) );
        }

        public String randomString(int i) {
            return "rs-" + i;
        }

        public String randomInt(int i, int j) {
            return "ri-" + i + ":" + "j";
        }

    }

无论传递给StandardEvaluationContext的任何对象都应具有这些方法.我将它们放在也运行表达式的同一个类中.

Whatever object you pass to StandardEvaluationContext should have those methods. I put them in the same class that also runs the expression.

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