http://github.com/FasterXML/jackson: Core annotations used for value types, used by Jackson data binding package. (FasterXML)
  • Tatu Saloranta 
package com.fasterxml.jackson.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


Marker annotation that can be used on a property accessor
(field, getter or setter, constructor parameter) to indicate that
the property is to contain type id to use when including
polymorphic type information.
Annotation should only be used if the intent is to override
generation of standard type id: if so, value of the property will be
accessed during serialization and used as the type id.

 On deserialization annotation has no effect, as visibility of type id is governed by value of JsonTypeInfo.visible; properties with this annotation get no special handling. 
 On serialization, this annotation will exclude property from being serialized along other properties; instead, its value is serialized as the type identifier. Since type identifier may be included in various places, it may still appear like 'normal' property (when using As.PROPERTY), but is more commonly embedded in a different place, as per inclusion rules (see JsonTypeInfo for details). 
Since:2.0
/**
 * Marker annotation that can be used on a property accessor
 * (field, getter or setter, constructor parameter) to indicate that
 * the property is to contain type id to use when including
 * polymorphic type information.
 * Annotation should <b>only be used</b> if the intent is to override
 * generation of standard type id: if so, value of the property will be
 * accessed during serialization and used as the type id.
 *<p>
 * On deserialization annotation has no effect, as visibility of type id
 * is governed by value of {@link JsonTypeInfo#visible}; properties with
 * this annotation get no special handling.
 *<p>
 * On serialization, this annotation will exclude property from being
 * serialized along other properties; instead, its value is serialized
 * as the type identifier. Since type identifier may be included in
 * various places, it may still appear like 'normal' property (when using
 * {@link JsonTypeInfo.As#PROPERTY}), but is more commonly embedded
 * in a different place, as per inclusion rules (see {@link JsonTypeInfo}
 * for details).
 * 
 * @since 2.0
 */
@Target({ElementType.ANNOTATION_TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@JacksonAnnotation
public @interface JsonTypeId
{

}