title: @Pattern , JSR303 bean validation : regex check max 5 words and not blank
body: <p>I use JSR303 bean validation annotations in my spring-mvc managed bean to validate text input.
  I need to check </p>
  
  <ul>
  <li>if a string contains max 5 words (Here a word is an alphabetic or alphanumeric string)
  and this string can't be blank (one space)</li>
  </ul>
  
  <p>I try with this : ( just to match 5 words)</p>
  
  <pre><code>@Pattern(message="max 5 words please" , regexp="^[a-zA-Z+#\-.0-9]{1,5}(\s[a-zA-Z+#\-.0-9]{1,5}){0,4}$")
  String keywords;
  </code></pre>
  
  <p>but my Eclipse IDE says  : 
  Invalid escape sequence (valid ones are  \b  \t  \n  \f  \r  \"  \'  \ )</p>