捕获JEXL中自定义函数引发的异常 [英] Catch exception thrown by custom function in JEXL

问题描述

我在JEXL引擎中添加了一些功能，这些功能可以在JEXL表达式中使用:

I added some functions to the JEXL engine wich can be used in the JEXL expressions:

Map<String, Object> functions = new HashMap<String, Object>();

mFunctions = new ConstraintFunctions();
functions.put(null, mFunctions);
mEngine.setFunctions(functions);

但是，某些函数会引发异常，例如:

However, some functions can throw exceptions, for example:

public String chosen(String questionId) throws NoAnswerException {
        Question<?> question = mQuestionMap.get(questionId);
        SingleSelectAnswer<?> answer = (SingleSelectAnswer<?>) question.getAnswer();
        if (answer == null) {
            throw new NoAnswerException(question);
        }
        return answer.getValue().getId();
}

当我解释一个表达式时，将调用自定义函数.该表达式当然包含对此函数的调用:

The custom function is called when i interpret an expression. The expression of course holds a call to this function:

String expression = "chosen('qID')";
Expression jexl = mEngine.createExpression(expression);
String questionId = (String) mExpression.evaluate(mJexlContext);

不幸的是，在解释过程中调用此函数时，如果它抛出NoAnswerException，则解释器不会向我派遣它，而是抛出通用的JEXLException.有什么方法可以从自定义函数中捕获异常?我为此使用了 apache commons JEXL 引擎，我的项目中的库jar.

Unfortunetaly, when this function is called in course of interpretation, if it throws the NoAnswerException, the interpreter does not propagete it to me, but throws a general JEXLException. Is there any way to catch exceptions from custom functions? I use the apache commons JEXL engine for this, which is used as a library jar in my project.

推荐答案

经过一番调查，我发现了一个简单的解决方案！

After some investigation, i found an easy solution!

在自定义函数中引发异常时，JEXL将引发常规JEXLException.但是，它巧妙地将原始异常包装在JEXLException中，特别是由于原因.因此，如果要捕捉原始图像，可以编写如下内容:

When an exception is thrown in a custom function, JEXL will throw a general JEXLException. However, it smartly wraps the original exception in the JEXLException, as it's cause in particular. So if we want to catch the original, we can write something like this:

try {
    String questionId = (String) mExpression.evaluate(mJexlContext);
} catch (JexlException e) {
    Exception original = e.getCause();
    // do something with the original
}

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