title: Struts2 Annotations validate String using RegexFieldValidator
body: <p>I am trying to use Struts2 Annotations to validate some fields of a bean.
  In this case, I would like to validate a phone number String with a regex.</p>
  
  <p>I found the <strong><code>@RegexFieldValidator</code></strong> annotation, so I included in my class and made some tests:</p>
  
  <pre><code>  @RequiredStringValidator(message="Phone required.") 
    @RegexFieldValidator( message="Invalid Phone",
      expression="\\([\\d][\\d][\\d]\\) [\\d][\\d][\\d]-[\\d][\\d][\\d][\\d]")
    public void setPhone(String phone) {
      this.phone = phone;
    }
  </code></pre>
  
  <p>However, the regex expression doesn´t work. I tried even with <strong>"\d{9}"</strong> and <strong>"[0-9]{9}"</strong>.
  Even with type=ValidatorType.SIMPLE.</p>
  
  <p>The Required StringValidator works properly...What´s going on here?
  Is it possible to use this validator properly?</p>
  
  <p>Thanks in advance</p>