org.codehaus.jackson.map
Class JsonDeserializer<T>

java.lang.Object
  extended by org.codehaus.jackson.map.JsonDeserializer<T>
Direct Known Subclasses:
BeanDeserializer, StdDeserializer

public abstract class JsonDeserializer<T>
extends java.lang.Object

Abstract class that defines API used by ObjectMapper (and other chained JsonDeserializers too) to deserialize Objects of arbitrary types from JSON, using provided JsonParser.


Constructor Summary
JsonDeserializer()
           
 
Method Summary
abstract  T deserialize(JsonParser jp, DeserializationContext ctxt)
          Method that can be called to ask implementation to deserialize json content into the value type this serializer handles.
 T deserialize(JsonParser jp, DeserializationContext ctxt, T intoValue)
          Alternate deserialization method (compared to the most commonly used, deserialize(JsonParser, DeserializationContext)), which takes in initialized value instance, which is to be configured and/or populated by deserializer.
 T getNullValue()
          Method that can be called to determine value to be used for representing null values (values deserialized when Json token is JsonToken.VALUE_NULL).
 boolean shouldBeCached()
          Method called to determine if this deserializer can and should be cached by deserializer provider.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

JsonDeserializer

public JsonDeserializer()
Method Detail

deserialize

public abstract T deserialize(JsonParser jp,
                              DeserializationContext ctxt)
                       throws java.io.IOException,
                              JsonProcessingException
Method that can be called to ask implementation to deserialize json content into the value type this serializer handles. Returned instance is to be constructed by method itself.

Pre-condition for this method is that the parser points to the first event that is part of value to deserializer (and which is never Json 'null' literal, more on this below): for simple types it may be the only value; and for structured types the Object start marker. Post-condition is that the parser will point to the last event that is part of deserialized value (or in case deserialization fails, event that was not recognized or usable, which may be the same event as the one it pointed to upon call).

Note that this method is never called for JSON null literal, and thus deserializers need (and should) not check for it.

Parameters:
jp - Parsed used for reading Json content
ctxt - Context that can be used to access information about this deserialization activity.
Returns:
Deserializer value
Throws:
java.io.IOException
JsonProcessingException

deserialize

public T deserialize(JsonParser jp,
                     DeserializationContext ctxt,
                     T intoValue)
              throws java.io.IOException,
                     JsonProcessingException
Alternate deserialization method (compared to the most commonly used, deserialize(JsonParser, DeserializationContext)), which takes in initialized value instance, which is to be configured and/or populated by deserializer. Method is only used for subset of all supported types; most commonly just for Collections and Maps, but potentially also for beans/POJOs.

Default implementation just throws UnsupportedOperationException, to indicate that types that do not explicitly add support do not expect to get the call.

Throws:
java.io.IOException
JsonProcessingException

getNullValue

public T getNullValue()
Method that can be called to determine value to be used for representing null values (values deserialized when Json token is JsonToken.VALUE_NULL). Usually this is simply Java null, but for some types (primitives) it may be necessary to use actual values.

Note that deserializers are allowed to call this just once and then reuse returned value; that is, method is not guaranteed to be called once for each conversion.

Default implementation simply returns null.


shouldBeCached

public boolean shouldBeCached()
Method called to determine if this deserializer can and should be cached by deserializer provider. This means that deserializer must be reusable for deserializing other instances of the type it was created to deserialize, as well as that it is somewhat costly to construct. Usually this only applies to bean type deserializers.

Default implementation returns false, which means that no caching will be done by deserializer provider. Without caching deserializer factory will be called every time a property of matching type is encountered during construction of root-level deserializers.

NOTE: this method will NOT be called when accessing "root" deserializers (type passed to ObjectMapper), but only when resolving dependant deserializers. As such it is acceptable to return false without worrying about performance impacts. Root-level caching should usually be enough for all non-bean types.

Since:
0.9.9-4