How to convert List to Json in Java

How to convert generic list to json in Java.I have class like this..

public class Output
{
    public int Keyname { get; set; }
    public Object  outputvalue{ get; set; }  //outvalue may be even a object collection
}

List<Output> outputList = new List<Output>();

I want to convert outputList into json in Java.After converting i will send it to client.