How to return Java Exception info to jQuery.ajax REST call?

Question

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.

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"
        }
    });
}

Answer 1

I was able to send a custom error message (java String) back to a jQuery based client this way. I think my custom message can be replaced with the exception info you want/need

in Controller:

public static void handleRuntimeException(Exception ex, HttpServletResponse 
                                          response,String message) {
        logger.error(ex);
        response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        response.getWriter().write(message);
        response.flushBuffer();
}

In client/javascript (called from ajax on error event)

displayError:function(jqXHR, textStatus, errorThrown){
   if(jqXHR.responseText !== ''){
        alert(textStatus+": "+jqXHR.responseText);
    }else{
        alert(textStatus+": "+errorThrown);
    }  
}

Hope this helps/

Answer 2

Use the servlet response object's sendError method, which lets you set the status code and status text message.

Documentation

Example EDIT

The jqXHR parameter gives you access to all of the response information including the status message.

jqXHR.statusText will give you the status message passed in to the sendError method.

If you need more than a short message you can write data to the response output and get that from jqXHR.responseText or jqXHR.responseXML .