com.fasterxml.jackson.databind.deser.std

## Class DelegatingDeserializer

- java.lang.Object
- - com.fasterxml.jackson.databind.JsonDeserializer<T>
  - - com.fasterxml.jackson.databind.deser.std.StdDeserializer<Object>
    - - com.fasterxml.jackson.databind.deser.std.DelegatingDeserializer

- All Implemented Interfaces:
    ContextualDeserializer, NullValueProvider, ResolvableDeserializer, Serializable

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

  Base class that simplifies implementations of `JsonDeserializer`s 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`

  - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected JsonDeserializer<?>` | `_delegatee`

    - ### Fields inherited from class com.fasterxml.jackson.databind.deser.std.StdDeserializer

      `_valueClass, _valueType, F_MASK_ACCEPT_ARRAYS, F_MASK_INT_COERCIONS`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `DelegatingDeserializer(JsonDeserializer<?> d)`

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    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.
    `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.
    `Object` | `deserialize(JsonParser p, DeserializationContext ctxt, 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.
    `Object` | `deserializeWithType(JsonParser p, DeserializationContext ctxt, TypeDeserializer typeDeserializer)` Base implementation that does not assume specific type inclusion mechanism.
    `SettableBeanProperty` | `findBackReference(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.
    `Object` | `getEmptyValue(DeserializationContext ctxt)` Method called to determine value to be used for "empty" values (most commonly when deserializing from empty JSON Strings).
    `Collection<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()` This method may be called in conjunction with calls to `JsonDeserializer.getNullValue(DeserializationContext)`, to check whether it needs to be called just once (static values), or each time empty value is needed.
    `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).
    `protected abstract JsonDeserializer<?>` | `newDelegatingInstance(JsonDeserializer<?> newDelegatee)`
    `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.
    `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

      `_byteOverflow, _coercedTypeDesc, _coerceEmptyString, _coerceIntegral, _coerceNullToken, _coerceTextualNull, _deserializeFromArray, _deserializeFromEmpty, _deserializeWrappedValue, _failDoubleToIntCoercion, _findNullProvider, _hasTextualNull, _intOverflow, _isEmptyOrTextualNull, _isIntNumber, _isNaN, _isNegInf, _isPosInf, _neitherNull, _nonNullNumber, _parseBooleanFromInt, _parseBooleanPrimitive, _parseBytePrimitive, _parseDate, _parseDate, _parseDateFromArray, _parseDoublePrimitive, _parseDoublePrimitive, _parseFloatPrimitive, _parseFloatPrimitive, _parseIntPrimitive, _parseIntPrimitive, _parseLongPrimitive, _parseLongPrimitive, _parseShortPrimitive, _parseString, _reportFailedNullCoerce, _shortOverflow, _verifyEndArrayForSingle, _verifyNullForPrimitive, _verifyNullForPrimitiveCoercion, _verifyNullForScalarCoercion, _verifyNumberForScalarCoercion, _verifyStringForScalarCoercion, findContentNullProvider, findContentNullStyle, findConvertingContentDeserializer, findDeserializer, findFormatFeature, findFormatOverrides, findValueNullProvider, getValueClass, getValueType, getValueType, handledType, handleMissingEndArrayForSingle, handleUnknownProperty, isDefaultDeserializer, isDefaultKeyDeserializer, parseDouble`

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

      `deserializeWithType, getEmptyAccessPattern, getEmptyValue, getNullValue, unwrappingDeserializer`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### _delegatee

          protected final JsonDeserializer<?> _delegatee

  - ### Constructor Detail

    - #### DelegatingDeserializer

          public DelegatingDeserializer(JsonDeserializer<?> d)

  - ### Method Detail

    - #### newDelegatingInstance

          protected abstract JsonDeserializer<?> newDelegatingInstance(JsonDeserializer<?> newDelegatee)

    - #### 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<Object>`

    - #### deserialize

          public Object deserialize(JsonParser p,
                                    DeserializationContext ctxt)
                             throws 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.currentToken() == 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<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:
        `IOException`

    - #### deserialize

          public Object deserialize(JsonParser p,
                                    DeserializationContext ctxt,
                                    Object intoValue)
                             throws 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<Object>`
      Throws:
        `IOException`

    - #### deserializeWithType

          public Object deserializeWithType(JsonParser p,
                                            DeserializationContext ctxt,
                                            TypeDeserializer typeDeserializer)
                                     throws 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<Object>`
        `typeDeserializer` - Deserializer to use for handling type information
      Throws:
        `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<Object>`

    - #### supportsUpdate

          public 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<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<Object>`
      Returns:
        Deserializer this deserializer delegates calls to, if null; null otherwise.

    - #### findBackReference

          public SettableBeanProperty findBackReference(String logicalName)

      Description copied from class: `JsonDeserializer`
      Method needed by `BeanDeserializerFactory` to properly link managed- and back-reference pairs.
      Overrides:
        `findBackReference` in class `JsonDeserializer<Object>`

    - #### getNullAccessPattern

          public AccessPattern getNullAccessPattern()

      Description copied from class: `JsonDeserializer`
      This method may be called in conjunction with calls to `JsonDeserializer.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 "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<Object>`

    - #### getNullValue

          public 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.

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

      Default implementation simply returns null.

      Specified by:
        `getNullValue` in interface `NullValueProvider`
      Overrides:
        `getNullValue` in class `JsonDeserializer<Object>`
      Throws:
        `JsonMappingException`

    - #### getEmptyValue

          public 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 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 `JsonDeserializer.getEmptyAccessPattern()` returns.

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

      Overrides:
        `getEmptyValue` in class `JsonDeserializer<Object>`
      Throws:
        `JsonMappingException`

    - #### getKnownPropertyNames

          public Collection<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<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<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.

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