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.<\/p>\n
Consider this simple controller:<\/p>\n
<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 \/>\n<\/code><\/pre>\nAnd now, with finger crossed… We have a winner!<\/p>\n
<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 \/>\n<\/code><\/pre>\nAs you can see only grails.converters.<span class=\"class\">JSON<\/span><\/code> converts your response to JSON format. There is no such converter for net.sf.json.<span class=\"class\">JSON<\/span><\/code>, so Grails has no converter to apply and it renders Map normally.<\/p>\n