com.fasterxml.jackson.databind.deser.std

Class FromStringDeserializer<T>

  • All Implemented Interfaces:
    NullValueProvider, ValueInstantiator.Gettable, Serializable
    Direct Known Subclasses:
    CoreXMLDeserializers.Std, DOMDeserializer, FromStringDeserializer.Std, UUIDDeserializer

    public abstract class FromStringDeserializer<T>
extends StdScalarDeserializer<T>
    Base class for simple deserializers that serialize values from String representation: this includes JSON Strings and other Scalar values that can be coerced into text, like Numbers and Booleans). Simple JSON String values are trimmed using String.trim(). Partial deserializer implementation will try to first access current token as a String, calls _deserialize(String,DeserializationContext) and returns return value. If this does not work (current token not a simple scalar type), attempts are made so that:
    • Embedded values (JsonToken.VALUE_EMBEDDED_OBJECT) are returned as-is if they are of compatible type
    • Arrays may be "unwrapped" if (and only if) DeserializationFeature.UNWRAP_SINGLE_VALUE_ARRAYS is enabled, and array contains just a single scalar value that can be deserialized (for example, JSON Array with single JSON String element).

    Special handling includes:

    See Also:
    Serialized Form

    • Constructor Detail

      • FromStringDeserializer

        protected FromStringDeserializer(Class<?> vc)

    • Method Detail

      • types

        public static Class<?>[] types()

      • findDeserializer

        public static FromStringDeserializer<?> findDeserializer(Class<?> rawType)
        Factory method for trying to find a deserializer for one of supported types that have simple from-String serialization.

      • logicalType

        public LogicalType logicalType()
        Description copied from class: JsonDeserializer
        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.
        Overrides:
        logicalType in class StdScalarDeserializer<T>
        Returns:
        Logical type of values this deserializer produces, if known; null if not

      • deserialize

        public T deserialize(com.fasterxml.jackson.core.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).

        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().

        Specified by:
        deserialize in class JsonDeserializer<T>
        Parameters:
        p - Parser used for reading JSON content
        ctxt - Context that can be used to access information about this deserialization activity.
        Returns:
        Deserialized value
        Throws:
        IOException

      • _shouldTrim

        protected boolean _shouldTrim()

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