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

Custom deserializers should usually not directly extend this class, but instead extend com.fasterxml.jackson.databind.deser.std.StdDeserializer (or its subtypes like com.fasterxml.jackson.databind.deser.std.StdScalarDeserializer).

If deserializer is an aggregate one -- meaning it delegates handling of some of its contents by using other deserializer(s) -- it typically also needs to implement com.fasterxml.jackson.databind.deser.ResolvableDeserializer, which can locate dependant deserializers. This is important to allow dynamic overrides of deserializers; separate call interface is needed to separate resolution of dependant deserializers (which may have cyclic link back to deserializer itself, directly or indirectly).

In addition, to support per-property annotations (to configure aspects of deserialization on per-property basis), deserializers may want to implement com.fasterxml.jackson.databind.deser.ContextualDeserializer, which allows specialization of deserializers: call to com.fasterxml.jackson.databind.deser.ContextualDeserializer.createContextual(com.fasterxml.jackson.databind.DeserializationContext,com.fasterxml.jackson.databind.BeanProperty) is passed information on property, and can create a newly configured deserializer for handling that particular property.

If both com.fasterxml.jackson.databind.deser.ResolvableDeserializer and com.fasterxml.jackson.databind.deser.ContextualDeserializer are implemented, resolution of deserializers occurs before contextualization.

 
 public abstract class JsonDeserializer<T>
 {
     /*
     /**********************************************************
     /* Main deserialization methods
     /**********************************************************
      */
    
    
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
 
     public abstract T deserialize(JsonParser jpDeserializationContext ctxt)
         throws IOExceptionJsonProcessingException;

    
Alternate deserialization method (compared to the most commonly used, deserialize(com.fasterxml.jackson.core.JsonParser,com.fasterxml.jackson.databind.DeserializationContext)), which takes in initialized value instance, to be configured and/or populated by deserializer. Method is not necessarily used for all supported types; most commonly it is used for Collections and Maps.

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

 
     public T deserialize(JsonParser jpDeserializationContext ctxt,
                          T intoValue)
         throws IOExceptionJsonProcessingException
     {
         throw new UnsupportedOperationException("Can not update object of type "+intoValue.getClass().getName());
     }

    
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 Deserializer to use for handling type information
            TypeDeserializer typeDeserializer)
        throws IOExceptionJsonProcessingException
    {
        // We could try calling 
        return typeDeserializer.deserializeTypedFromAny(jpctxt);
    }
    /*
    /**********************************************************
    /* Fluent factory methods for constructing decorated versions
    /**********************************************************
     */

    
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

        return this;
    }

    
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 java.lang.UnsupportedOperationException (if operation does not make sense or is not allowed); or return this deserializer as is.

Since:
2.1
    public JsonDeserializer<?> replaceDelegatee(JsonDeserializer<?> delegatee) {
        throw new UnsupportedOperationException();
    }
    
    /*
    /**********************************************************
    /* Other accessors
    /**********************************************************
     */
    
    
Method that can be called to determine value to be used for representing null values (values deserialized when JSON token is com.fasterxml.jackson.core.JsonToken.VALUE_NULL). Usually this is simply Java null, but for some types (especially primitives) it may be necessary to use non-null 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.

    public T getNullValue() { return null; }

    
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 types. Or, if type should never be converted from empty String, method can also throw an exception.

Default implementation simple calls getNullValue() and returns value.

    public T getEmptyValue() { return getNullValue(); }

    
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
        return null;
    }
    
    
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.

    public boolean isCachable() { return false; }

    
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 can not 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 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
    public ObjectIdReader getObjectIdReader() { return null; }

    
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:
Deserializer this deserializer delegates calls to, if null; null otherwise.
Since:
2.1
    public JsonDeserializer<?> getDelegatee() {
        return null;
    }
    
    /*
    /**********************************************************
    /* Helper classes
    /**********************************************************
     */

    
This marker class is only to be used with annotations, to indicate that no deserializer is configured.

Specifically, this class is to be used as the marker for annotation com.fasterxml.jackson.databind.annotation.JsonDeserialize

    public abstract static class None extends JsonDeserializer<Object> {
        private None() { } // not to be instantiated
    }
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