title: How to provide custom Expression or Predicate with JPA QueryBuilder
body: <p>I am using JPA2 (EclipseLink implementation) with Spring Data and using Specification pattern to provide filter specification.</p>
  
  <p>How can I introduce custom Expression or Predicate that will map to custom SQL operator? I have particularly in mind using PostgreSQL FTS extension and add conditions like this:</p>
  
  <pre><code>SELECT ... WHERE ... AND column @@ 'ts query'   
  </code></pre>
  
  <p>to my Specification instance.</p>