Package name.martingeisse.grumpyjson.deserialize

Interface JsonDeserializer

All Known Implementing Classes:
BooleanConverter, EnumConverter, FieldMustBeNullConverter, IgnoredFieldConverter, IntegerConverter, JsonElementConverter, ListConverter, LocalDateConverter, LocalDateTimeConverter, LocalTimeConverter, LongConverter, MapConverter, NullableFieldConverter, OptionalFieldConverter, RecordConverter, StringConverter
public interface JsonDeserializer
Defines the conversion from JSON to a Java object / value for one or more types.

The JSON side is represented by JsonElement. That is, parsing the JSON syntax is out-of-scope for this interface. Only mapping the higher-level structure is done here.

Deserializing JSON is driven by the Type to deserialize. This is crucial because there is otherwise no information about the Java class to generate from it. The class alone might not be enough though. This is most obvious when deserializing an array to a List: Even when the caller specifies to deserialize the List class, the deserializer will fail for the list elements because the element type is unknown. Therefore the deserializer gets passed the whole type, such as List<Integer>, so it knows to deserialize the elements as Integer.

There is no precedence rule for deserializers based on specificity: If one deserializer supports supertype A, and a second one supports subtype B of A, then for an instance of B, the second one does NOT take precedence just because it is more specific. Instead, the registry will select the deserializer that was registered later.

  • Method Details

    • supportsTypeForDeserialization

      boolean supportsTypeForDeserialization(Type type)
      Checks if this deserializer supports the specified type.
      Parameters:
      type - the type to check
      Returns:
      true if supported, false if not

    • deserialize

      Object deserialize(com.google.gson.JsonElement json, Type type) throws JsonDeserializationException
      Converts a value from JSON.

      This method must not be called with a type for which supportsTypeForDeserialization(Type) returns false. Calling it with such types anyway results in undefined behavior.

      Parameters:
      json - the JSON
      type - the type to deserialize
      Returns:
      the deserialized value
      Throws:
      JsonDeserializationException - if the JSON does not match the expected structure

    • deserializeAbsent

      default Object deserializeAbsent(Type type) throws JsonDeserializationException
      Converts a value from an absent JSON fragment. This can be used to return a default for optional object properties.

      The standard implementation of this method is that missing values are not tolerated, and throws an exception.

      This method must not be called with a type for which supportsTypeForDeserialization(Type) returns false. Calling it with such types anyway results in undefined behavior.

      Parameters:
      type - the type to deserialize
      Returns:
      the default value for that type
      Throws:
      JsonDeserializationException - if the JSON does not match the expected structure