title: How to return Java Exception info to jQuery.ajax REST call?
body: <p>I have some jQuery code that makes a REST call to a Java back end.  Processing of the back end function could encounter an Exception.  What is the best way to get this information back up to Javascript?  In a test I caught the exception in Java and set the HTTP status code to 500.  This caused the $.ajax error handler to be called, as expected. the args to the error handler don't really contain any useful information.  I'd ideally like to propagate the Exception.getMessage() string back to the error handler somehow, but don't know how.</p>
  
  <pre>
  <code>
  function handleClick() {
      var url = '/backend/test.json';
      $.ajax({
          type: "POST",
          url: url,
          cache: false,
          dataType: "json",
          success: function(data){
              alert("it worked");
          },
          error: function(jqXHR, textStatus, errorThrown) {
              alert(jqXHR);
              alert(textStatus); // this comes back as "error"
              alert(errorThrown); // this comes back as "undefined"
          }
      });
  }
  </code>
  </pre>