http://github.com/FasterXML/jackson: General data-binding functionality for Jackson: works on core streaming API (FasterXML)
  • Tatu Saloranta
  • Christopher Currie
  • Paul Brown 
package com.fasterxml.jackson.databind.deser;

import com.fasterxml.jackson.databind.*;


Add-on interface that JsonDeserializers can implement to get a callback that can be used to create contextual (context-dependent) instances of deserializer to use for handling properties of supported type. This can be useful for deserializers that can be configured by annotations, or should otherwise have differing behavior depending on what kind of property is being deserialized. 
 Note that in cases where deserializer needs both contextualization and resolution -- that is, implements both this interface and ResolvableDeserializer -- resolution via ResolvableDeserializer occurs first, and contextual resolution (via this interface) later on. 
/**
 * Add-on interface that {@link JsonDeserializer}s can implement to get a callback
 * that can be used to create contextual (context-dependent) instances of
 * deserializer to use for  handling properties of supported type.
 * This can be useful
 * for deserializers that can be configured by annotations, or should otherwise
 * have differing behavior depending on what kind of property is being deserialized.
 *<p>
 * Note that in cases where deserializer needs both contextualization and
 * resolution -- that is, implements both this interface and {@link ResolvableDeserializer}
 * -- resolution via {@link ResolvableDeserializer} occurs first, and contextual
 * resolution (via this interface) later on.
 */
public interface ContextualDeserializer
{
    
Method called to see if a different (or differently configured) deserializer
is needed to deserialize values of specified property.
Note that instance that this method is called on is typically shared one and
as a result method should NOT modify this instance but rather construct
and return a new instance. This instance should only be returned as-is, in case
it is already suitable for use.

Params:
  • ctxt – Deserialization context to access configuration, additional 
   deserializers that may be needed by this deserializer
  • property – Method, field or constructor parameter that represents the property
  (and is used to assign deserialized value).
  Should be available; but there may be cases where caller cannot provide it and
  null is passed instead (in which case impls usually pass 'this' deserializer as is)
Throws:
Returns:Deserializer to use for deserializing values of specified property;
  may be this instance or a new instance.
/**
     * Method called to see if a different (or differently configured) deserializer
     * is needed to deserialize values of specified property.
     * Note that instance that this method is called on is typically shared one and
     * as a result method should <b>NOT</b> modify this instance but rather construct
     * and return a new instance. This instance should only be returned as-is, in case
     * it is already suitable for use.
     * 
     * @param ctxt Deserialization context to access configuration, additional 
     *    deserializers that may be needed by this deserializer
     * @param property Method, field or constructor parameter that represents the property
     *   (and is used to assign deserialized value).
     *   Should be available; but there may be cases where caller cannot provide it and
     *   null is passed instead (in which case impls usually pass 'this' deserializer as is)
     * 
     * @return Deserializer to use for deserializing values of specified property;
     *   may be this instance or a new instance.
     * 
     * @throws JsonMappingException
     */
    public JsonDeserializer<?> createContextual(DeserializationContext ctxt,
            BeanProperty property)
        throws JsonMappingException;
}