Grails render as JSON catch

One of a reasons your controller doesn’t render a proper response in JSON format might be wrong package name that you use. It is easy to overlook. Import are on top of a file, you look at your code and everything seems to be fine. Except response is still not in JSON format.

Consider this simple controller:

<span class="keyword">class</span> <span class="class">RestJsonCatchController</span> {<br />    <span class="keyword">def</span> <span class="method">grailsJson</span>() {<br />        <span class="method">render</span>([<span class="field">first</span>: <span class="string">'foo'</span>, <span class="field">second</span>: <span class="number">5</span>] <span class="keyword">as</span> grails.converters.<span class="class">JSON</span>)<br />    }<br /><br />    <span class="keyword">def</span> <span class="method">netSfJson</span>() {<br />        <span class="method">render</span>([<span class="field">first</span>: <span class="string">'foo'</span>, <span class="field">second</span>: <span class="number">5</span>] <span class="keyword">as</span> net.sf.json.<span class="class">JSON</span>)<br />    }<br />}<br />

And now, with finger crossed… We have a winner!

<span class="keyword">$</span> curl localhost:8080/example/restJsonCatch/grailsJson<br />{"first":"foo","second":5}<br /><span class="keyword">$</span> curl localhost:8080/example/restJsonCatch/netSfJson<br />{first=foo, second=5}<br />

As you can see only grails.converters.<span class="class">JSON</span> converts your response to JSON format. There is no such converter for net.sf.json.<span class="class">JSON</span>, so Grails has no converter to apply and it renders Map normally.

Conclusion: always carefully look at your imports if you’re working with JSON in Grails!

Edit: Burt suggested that this is a bug. I’ve submitted JIRA issue here: GRAILS-9622 render as class that is not a codec should throw exception