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",
          ...
      }
  

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

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).

Handling null values (JsonToken.VALUE_NULL)
: Note that this method is never called for the JSON null literal to avoid every deserializer from having to handle null values. Instead, the JsonDeserializer#getNullValue(DeserializationContext) method is called to produce a null value. To influence null handling, custom deserializers should override JsonDeserializer#getNullValue(DeserializationContext) and usually also JsonDeserializer#getNullAccessPattern().

Parameters

p:JsonParser

Parser used for reading JSON content

ctxt:DeserializationContext

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

Returns:T

Deserialized value

Alternate deserialization method (compared to the most commonly used, 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)

Deserialization called when type being deserialized is defined to contain additional type identifier, to allow for correctly instantiating correct subtype. This can be due to annotation on type (or its supertype), or due to global settings without annotations.

Default implementation may work for some types, but ideally subclasses should not rely on current default implementation. Implementation is mostly provided to avoid compilation errors with older code.

Parameters

typeDeserializer:TypeDeserializer

Deserializer to use for handling type information

Method similar to deserializeWithType(JsonParser, DeserializationContext, TypeDeserializer) but called when merging value. Considered "bad merge" by default implementation, but if MapperFeature#IGNORE_MERGE_FOR_UNMERGEABLE is enabled will simple delegate to deserializeWithType(JsonParser, DeserializationContext, TypeDeserializer).

Since

2.10

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

Since

2.2 (was moved out of BeanDeserializerBase)

Overrides default com.fasterxml.jackson.databind.deser.NullValueProvider.getAbsentValue.

Method called to determine placeholder value to be used for cases where no value was obtained from input but we must pass a value nonetheless: the common case is that of Creator methods requiring passing a value for every parameter. Usually this is same as getNullValue (which in turn is usually simply Java null), but it can be overridden for specific types: most notable scalar types must use "default" values.

This method needs to be called every time a determination is made.

Default implementation simply calls getNullValue and returns value.

Annotations

@Override

Since

2.13

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.

Returns:JsonDeserializer<?>

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

Since

2.1

This method may be called in conjunction with calls to getEmptyValue(DeserializationContext), to check whether it needs to be called just once (static values), or each time empty value is needed.

Since

2.9

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

This method may be called once, or multiple times, depending on what getEmptyAccessPattern() returns.

Default implementation simply calls getNullValue and returns value.

Since

2.6 Added to replace earlier no-arguments variant

Annotations

@Deprecated

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).

Since

2.0

Implements com.fasterxml.jackson.databind.deser.NullValueProvider.getNullAccessPattern.

This method may be called in conjunction with calls to getNullValue(DeserializationContext), to check whether it needs to be called just once (static values), or each time empty value is needed.

Default implementation indicates that the "null value" to use for input null does not vary across uses so that getNullValue(DeserializationContext) need not be called more than once per deserializer instance. This information may be used as optimization.

Annotations

@Override

Implements com.fasterxml.jackson.databind.deser.NullValueProvider.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 (especially primitives) it may be necessary to use non-null values.

This method may be called once, or multiple times, depending on what getNullAccessPattern() returns.

Default implementation simply returns null.

Annotations

@Override

Since

2.6 Added to replace earlier no-arguments variant

Annotations

@Deprecated

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 com.fasterxml.jackson.databind.deser.BeanDeserializer) do implement this feature, and may return reader instance, depending on exact configuration of instance (which is based on type, and referring property).

Returns:ObjectIdReader

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.

Since

2.0

Method for accessing concrete physical type of values this deserializer produces. Note that this information is not guaranteed to be exact -- it may be a more generic (super-type) -- but it should not be incorrect (return a non-related type).

Default implementation will return null, which means almost same same as returning Object.class would; that is, that nothing is known about handled type.

Returns:Class<?>

Physical type of values this deserializer produces, if known; null if not

Since

2.3

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 com.fasterxml.jackson.databind.deser.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.

Method for accessing logical type of values this deserializer produces. Typically used for further configuring handling of values, for example, to find which coercions are legal.

Returns:LogicalType

Logical type of values this deserializer produces, if known; null if not

Since

2.12

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.

Since

2.1

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 deserializer 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.

Since

2.9

Method that will return deserializer instance that is able to handle "unwrapped" value instances If no unwrapped instance can be constructed, will simply return this object as-is.

Default implementation just returns 'this' indicating that no unwrapped variant exists