title: is SpelExpression thread safe?
body: <p>Specifically, can getValue(StandardEvaluationContext, Class) safely be called from multiple threads on the same SpelExpression with different contexts?</p>
  
  <p>I saw this question asked and answered by Gary Russell from Spring Source.  However, I also see people reporting concurrency issues.  I looked through the source code of related Spring classes and I can't be sure.</p>
  
  <p>I would like to get a definite answer from Spring developers who've worked with spring-el or from Spring users who've used this class in heavily concurrent environment.</p>
  
  <p>Thanks.</p>