Java 寻找表达式评估器

Looking for an expression evaluator

提问by Stroboskop

I'm looking for an evaluator for simple condition expressions. Expressions should include variables (read only), strings, numbers and some basic operators.

我正在寻找一个简单条件表达式的评估器。表达式应包括变量（只读）、字符串、数字和一些基本运算符。

E.g. expressions something like this:

例如像这样的表达式：

${a} == "Peter" && ( ${b} == null || ${c} > 10 )

So far i implemented a rather "magical" parser that returns an AST that i can evaluate, but i can't believe that i'm the first one to solve that problem.

到目前为止，我实现了一个相当“神奇”的解析器，它返回一个我可以评估的 AST，但我不敢相信我是第一个解决这个问题的人。

What existing code could i use instead?

我可以改用什么现有代码？

采纳答案by NightWolf

What about SPEL (Spring Expression Lang); http://static.springsource.org/spring/docs/3.0.x/reference/expressions.html

SPEL（Spring Expression Lang）呢？http://static.springsource.org/spring/docs/3.0.x/reference/expressions.html

回答by Hyman

Why don't you use Rhino? It's a JavaScript engine already present inside the JDK.

你为什么不使用犀牛？它是一个已经存在于 JDK 中的 JavaScript 引擎。

It can evaluate whatever you like to write in JS.. take a look here

它可以评估您喜欢用 JS 编写的任何内容.. 看看这里

回答by trashgod

This simple recursive descent parserevaluates constants as named functions having no parameters.

这个简单的递归下降解析器将常量评估为没有参数的命名函数。

回答by Mike Daniels

Sounds like JEXLmight work well for you. Check out its syntax reference.

听起来JEXL可能适合您。查看其语法参考。

回答by andersoj

Have you looked at MVEL? They provide a getting started guideand performance analysis.

你看过MVEL吗？它们提供了入门指南和性能分析。

Here's one of their simple examples:

这是他们的简单示例之一：

// The compiled expression is serializable and can be cached for re-use.
CompiledExpression compiled = MVEL.compileExpression("x * y"); 

Map vars = new HashMap();
vars.put("x", new Integer(5));
vars.put("y", new Integer(10));

// Executes the compiled expression
Integer result = (Integer) MVEL.executeExpression(compiled, vars); 
assert result.intValue() == 50; 

Also (answering my own question) MVEL seems to provide some support for bytecode generation.

另外（回答我自己的问题）MVEL 似乎为字节码生成提供了一些支持。

Other alternatives, culling from the above answers and my own:

其他替代方案，从上述答案和我自己的答案中剔除：

• Java Expression Parser (JEP)-- and note there is an old version available for free
• Apache Commons JEXL
• With regard to Rhino, here's a dudewho did some arithmetic evaluation in that context (looks messy)

• Java Expression Parser (JEP)-- 请注意有一个免费的旧版本
• Apache Commons JEXL
• 关于 Rhino，这里有一个在这种情况下做了一些算术评估的家伙（看起来很乱）

回答by Scorpion

A very simple and easy to use alternativewith a lot of built in excel functions for string, date and number formatting.

一个非常简单且易于使用的替代方案，具有许多用于字符串、日期和数字格式的内置 excel 函数。

The library also allows easy addition of custom functions. A lot of examples available on the git page. A simple example using variables

该库还允许轻松添加自定义功能。git 页面上提供了很多示例。使用变量的简单示例

  ExpressionsEvaluator evalExpr = ExpressionsFactory.create("LEFT(City, 3)");
  Map<String, Object> variables = new HashMap<String, Object>();
  variables.put("City", "New York");
  assertEquals("New", evalExpr.eval(variables));

回答by Skyost

Hereis a little library I've worked on that supports expression evaluation (including variables, strings, boolean, etc...).

这是我研究过的一个支持表达式求值（包括变量、字符串、布尔值等）的小库。

A little example :

一个小例子：

String expression = "EXP(var)";
ExpressionEvaluator evaluator = new ExpressionEvaluator();
evaluator.putVariable(new Variable("var", VariableType.NUMBER, new BigDecimal(20)));

System.out.println("Value of exp(var) : " + evaluator.evaluate(expression).getValue());