package org.acme;

class ClassA
{
    String a;
    String b;
}

interface Entity {}
static class Person implements Entity {}

Genson genson = new Genson.Builder().setWithClassMetadata(true).create();
// json will be equal to {"@class":"my.package.Person"}
String json = genson.serialize(new Person());

// and now Genson is able to deserialize it back to Person using the information
// in the Json Object
Person person = (Person) genson.deserialize(json, Entity.class);

Genson genson = new Genson.Builder().addAlias("person", Person.class).create();
// json value is {"@class": "person"}
String json = genson.serialize(new Person());