FlexJSON

JavaScript Object Notation (aka JSON) is a very popular alternative to XML for transmitting data to the web browser. 
Flexjson is a lightweight library for serializing Java objects into JSON

@JSONアノテーションに，ちょっとビビっときた．

    public class User {
       private String login;
       private String hashedPassword;
       private Date lastLogin;

       @JSON(include=false)
       public String getHashedPassword() {
       }
    }

詳しくはこちら
http://flexjson.sourceforge.net/