com.fasterxml.jackson.databind.deser.std

Class DelegatingDeserializer

java.lang.Object

com.fasterxml.jackson.databind.JsonDeserializer<T>

com.fasterxml.jackson.databind.deser.std.StdDeserializer<java.lang.Object>

com.fasterxml.jackson.databind.deser.std.DelegatingDeserializer

All Implemented Interfaces:

ContextualDeserializer, NullValueProvider, ResolvableDeserializer, java.io.Serializable

public abstract class DelegatingDeserializer
extends StdDeserializer<java.lang.Object>
implements ContextualDeserializer, ResolvableDeserializer

Base class that simplifies implementations of JsonDeserializers that mostly delegate functionality to another deserializer implementation (possibly forming a chaing of deserializers delegating functionality in some cases)

Since:

2.1

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class com.fasterxml.jackson.databind.JsonDeserializer

JsonDeserializer.None

Constructor Summary

Constructors

Constructor and Description
DelegatingDeserializer(JsonDeserializer<?> d)

Method Summary

Modifier and Type	Method and Description
JsonDeserializer<?>	createContextual(DeserializationContext ctxt, BeanProperty property) Method called to see if a different (or differently configured) deserializer is needed to deserialize values of specified property.
java.lang.Object	deserialize(JsonParser p, DeserializationContext ctxt) Method that can be called to ask implementation to deserialize JSON content into the value type this serializer handles.
java.lang.Object	deserialize(JsonParser p, DeserializationContext ctxt, java.lang.Object intoValue) Alternate deserialization method (compared to the most commonly used, JsonDeserializer.deserialize(JsonParser, DeserializationContext)), which takes in initialized value instance, to be configured and/or populated by deserializer.
java.lang.Object	deserializeWithType(JsonParser p, DeserializationContext ctxt, TypeDeserializer typeDeserializer) Base implementation that does not assume specific type inclusion mechanism.
SettableBeanProperty	findBackReference(java.lang.String logicalName) Method needed by BeanDeserializerFactory to properly link managed- and back-reference pairs.
JsonDeserializer<?>	getDelegatee() Accessor that can be used to determine if this deserializer uses another deserializer for actual deserialization, by delegating calls.
java.lang.Object	getEmptyValue(DeserializationContext ctxt) Method called to determine value to be used for "empty" values (most commonly when deserializing from empty JSON Strings).
java.util.Collection<java.lang.Object>	getKnownPropertyNames() Method that will either return null to indicate that type being deserializers has no concept of properties; or a collection of identifiers for which toString will give external property name.
AccessPattern	getNullAccessPattern() Default implementation indicates that "null value" to use for input null is simply Java `null` for all deserializers, unless overridden by sub-classes.
java.lang.Object	getNullValue(DeserializationContext ctxt) Method that can be called to determine value to be used for representing null values (values deserialized when JSON token is JsonToken.VALUE_NULL).
ObjectIdReader	getObjectIdReader() Accessor that can be used to check whether this deserializer is expecting to possibly get an Object Identifier value instead of full value serialization, and if so, should be able to resolve it to actual Object instance to return as deserialized value.
boolean	isCachable() Method called to see if deserializer instance is cachable and usable for other properties of same type (type for which instance was created).
JsonDeserializer<?>	replaceDelegatee(JsonDeserializer<?> delegatee) Method that can be called to try to replace deserializer this deserializer delegates calls to.
void	resolve(DeserializationContext ctxt) Method called after deserializer instance has been constructed (and registered as necessary by provider objects), but before it has returned it to the caller.
java.lang.Boolean	supportsUpdate(DeserializationConfig config) Introspection method that may be called to see whether deserializer supports update of an existing value (aka "merging") or not.

Methods inherited from class com.fasterxml.jackson.databind.deser.std.StdDeserializer

getValueClass, getValueType, handledType

Methods inherited from class com.fasterxml.jackson.databind.JsonDeserializer

getEmptyAccessPattern, getEmptyValue, getNullValue, unwrappingDeserializer

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DelegatingDeserializer

public DelegatingDeserializer(JsonDeserializer<?> d)

Method Detail

resolve

public void resolve(DeserializationContext ctxt)
             throws JsonMappingException

Description copied from interface: ResolvableDeserializer

Method called after deserializer instance has been constructed (and registered as necessary by provider objects), but before it has returned it to the caller. Called object can then resolve its dependencies to other types, including self-references (direct or indirect).

Specified by:

resolve in interface ResolvableDeserializer

Parameters:

ctxt - Context to use for accessing configuration, resolving secondary deserializers

Throws:

JsonMappingException

createContextual

public JsonDeserializer<?> createContextual(DeserializationContext ctxt,
                                            BeanProperty property)
                                     throws JsonMappingException

Description copied from 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.

Specified by:

createContextual in interface ContextualDeserializer

Parameters:

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)

Returns:

Deserializer to use for deserializing values of specified property; may be this instance or a new instance.

Throws:

JsonMappingException

replaceDelegatee

public JsonDeserializer<?> replaceDelegatee(JsonDeserializer<?> delegatee)

Description copied from class: JsonDeserializer

Method that can be called to try to replace deserializer this deserializer delegates calls to. If not supported (either this deserializer does not delegate anything; or it does not want any changes), should either throw UnsupportedOperationException (if operation does not make sense or is not allowed); or return this deserializer as is.

Overrides:

replaceDelegatee in class JsonDeserializer<java.lang.Object>

deserialize

public java.lang.Object deserialize(JsonParser p,
                                    DeserializationContext ctxt)
                             throws java.io.IOException

Description copied from class: JsonDeserializer

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 or a FIELD_NAME.

The two possible input conditions for structured types result from polymorphism via fields. In the ordinary case, Jackson calls this method when it has encountered an OBJECT_START, and the method implementation must advance to the next token to see the first field name. If the application configures polymorphism via a field, then the object looks like the following.

      {
          "@class": "class name",
          ...
      }
  

Jackson consumes the two tokens (the @class field name and its value) in order to learn the class and select the deserializer. Thus, the stream is pointing to the FIELD_NAME for the first field after the @class. Thus, if you want your method to work correctly both with and without polymorphism, you must begin your method with:

       if (p.getCurrentToken() == JsonToken.START_OBJECT) {
         p.nextToken();
       }
  

This results in the stream pointing to the field name, so that the two conditions align.

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.

Specified by:

deserialize in class JsonDeserializer<java.lang.Object>

Parameters:

p - Parsed used for reading JSON content

ctxt - Context that can be used to access information about this deserialization activity.

Returns:

Deserialized value

Throws:

java.io.IOException

deserialize

public java.lang.Object deserialize(JsonParser p,
                                    DeserializationContext ctxt,
                                    java.lang.Object intoValue)
                             throws java.io.IOException

Description copied from class: JsonDeserializer

Alternate deserialization method (compared to the most commonly used, JsonDeserializer.deserialize(JsonParser, DeserializationContext)), which takes in initialized value instance, to be configured and/or populated by deserializer. Method is not necessarily used (or supported) by all types (it will not work for immutable types, for obvious reasons): most commonly it is used for Collections and Maps. It may be used both with "updating readers" (for POJOs) and when Collections and Maps use "getter as setter".

Default implementation just throws UnsupportedOperationException, to indicate that types that do not explicitly add support do not necessarily support update-existing-value operation (esp. immutable types)

Overrides:

deserialize in class JsonDeserializer<java.lang.Object>

Throws:

java.io.IOException

deserializeWithType

public java.lang.Object deserializeWithType(JsonParser p,
                                            DeserializationContext ctxt,
                                            TypeDeserializer typeDeserializer)
                                     throws java.io.IOException

Description copied from class: StdDeserializer

Base implementation that does not assume specific type inclusion mechanism. Sub-classes are expected to override this method if they are to handle type information.

Overrides:

deserializeWithType in class StdDeserializer<java.lang.Object>

typeDeserializer - Deserializer to use for handling type information

Throws:

java.io.IOException

isCachable

public boolean isCachable()

Description copied from class: JsonDeserializer

Method called to see if deserializer instance is cachable and usable for other properties of same type (type for which instance was created).

Note that cached instances are still resolved on per-property basis, if instance implements ResolvableDeserializer: cached instance is just as the base. This means that in most cases it is safe to cache instances; however, it only makes sense to cache instances if instantiation is expensive, or if instances are heavy-weight.

Default implementation returns false, to indicate that no caching is done.

Overrides:

isCachable in class JsonDeserializer<java.lang.Object>

supportsUpdate

public java.lang.Boolean supportsUpdate(DeserializationConfig config)

Description copied from class: JsonDeserializer

Introspection method that may be called to see whether deserializer supports update of an existing value (aka "merging") or not. Return value should either be Boolean.FALSE if update is not supported at all (immutable values); Boolean.TRUE if update should usually work (regular POJOs, for example), or null if this is either not known, or may sometimes work.

Information gathered is typically used to either prevent merging update for property (either by skipping, if based on global defaults; or by exception during deserialization construction if explicit attempt made) if Boolean.FALSE returned, or inclusion if Boolean.TRUE is specified. If "unknown" case (null returned) behavior is to exclude property if global defaults used; or to allow if explicit per-type or property merging is defined.

Default implementation returns null to allow explicit per-type or per-property attempts.

Overrides:

supportsUpdate in class JsonDeserializer<java.lang.Object>

getDelegatee

public JsonDeserializer<?> getDelegatee()

Description copied from class: JsonDeserializer

Accessor that can be used to determine if this deserializer uses another deserializer for actual deserialization, by delegating calls. If so, will return immediate delegate (which itself may delegate to further deserializers); otherwise will return null.

Overrides:

getDelegatee in class JsonDeserializer<java.lang.Object>

Returns:

Deserializer this deserializer delegates calls to, if null; null otherwise.

findBackReference

public SettableBeanProperty findBackReference(java.lang.String logicalName)

Description copied from class: JsonDeserializer

Method needed by BeanDeserializerFactory to properly link managed- and back-reference pairs.

Overrides:

findBackReference in class JsonDeserializer<java.lang.Object>

getNullAccessPattern

public AccessPattern getNullAccessPattern()

Description copied from class: JsonDeserializer

Default implementation indicates that "null value" to use for input null is simply Java `null` for all deserializers, unless overridden by sub-classes. This information may be used as optimization.

Specified by:

getNullAccessPattern in interface NullValueProvider

Overrides:

getNullAccessPattern in class JsonDeserializer<java.lang.Object>

getNullValue

public java.lang.Object getNullValue(DeserializationContext ctxt)
                              throws JsonMappingException

Description copied from class: JsonDeserializer

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 (especially primitives) it may be necessary to use non-null values.

Since version 2.6 (in which the context argument was added), call is expected to be made each and every time a null token needs to be handled.

Default implementation simply returns null.

Specified by:

getNullValue in interface NullValueProvider

Overrides:

getNullValue in class JsonDeserializer<java.lang.Object>

Throws:

JsonMappingException

getEmptyValue

public java.lang.Object getEmptyValue(DeserializationContext ctxt)
                               throws JsonMappingException

Description copied from class: JsonDeserializer

Method called to determine value to be used for "empty" values (most commonly when deserializing from empty JSON Strings). Usually this is same as JsonDeserializer.getNullValue(com.fasterxml.jackson.databind.DeserializationContext) (which in turn is usually simply Java null), but it can be overridden for types. Or, if type should never be converted from empty String, method can also throw an exception.

Since version 2.6 (in which the context argument was added), call is expected to be made each and every time an empty value is needed.

Since version 2.9 does not require return of `T` any more.

Default implementation simply calls JsonDeserializer.getNullValue(com.fasterxml.jackson.databind.DeserializationContext) and returns value.

Overrides:

getEmptyValue in class JsonDeserializer<java.lang.Object>

Throws:

JsonMappingException

getKnownPropertyNames

public java.util.Collection<java.lang.Object> getKnownPropertyNames()

Description copied from class: JsonDeserializer

Method that will either return null to indicate that type being deserializers has no concept of properties; or a collection of identifiers for which toString will give external property name. This is only to be used for error reporting and diagnostics purposes (most commonly, to accompany "unknown property" exception).

Overrides:

getKnownPropertyNames in class JsonDeserializer<java.lang.Object>

getObjectIdReader

public ObjectIdReader getObjectIdReader()

Description copied from class: JsonDeserializer

Accessor that can be used to check whether this deserializer is expecting to possibly get an Object Identifier value instead of full value serialization, and if so, should be able to resolve it to actual Object instance to return as deserialized value.

Default implementation returns null, as support cannot be implemented generically. Some standard deserializers (most notably BeanDeserializer) do implement this feature, and may return reader instance, depending on exact configuration of instance (which is based on type, and referring property).

Overrides:

getObjectIdReader in class JsonDeserializer<java.lang.Object>

Returns:

ObjectIdReader used for resolving possible Object Identifier value, instead of full value serialization, if deserializer can do that; null if no Object Id is expected.