Oftentimes jqGrid is used in Java web app. Sometimes it is also the case that a Java based web service provides data for jqGrid.
jqGrid reads JSON data the faster than data in any other format. JSON is not native to the Java world, though.
Codemerx Java JSON Serializer for jqGrid steps in to bridge that gap. It makes use of the well known flexjson library. It comes as source code that could easily be integrated in your solution. Also, it is free and it comes under the MIT License that provides maximum flexibility of use.