Module tools.jackson.databind
Package tools.jackson.databind

Class ValueSerializer<T>

java.lang.Object
tools.jackson.databind.ValueSerializer<T>
All Implemented Interfaces:
JsonFormatVisitable
Direct Known Subclasses:
StdSerializer, TypeWrappedSerializer, ValueSerializer.None, ZonedDateTimeKeySerializer
public abstract class ValueSerializer<T> extends Object implements JsonFormatVisitable
Abstract class that defines API used by ObjectMapper (and other chained ValueSerializers too) to serialize Objects of arbitrary types into JSON, using provided JsonGenerator. Note that although API is defined here, custom serializer implementations should almost always be based on StdSerializer since it will implement many of optional methods of this class.

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

Initialization of serializers is handled by two main methods:

  1. resolve(tools.jackson.databind.SerializationContext): called after instance is configured to be used for specific type, but without yet knowing property it will be used for (or, in case of root values, without property). Method needs to be implemented for serializers that may work on cyclic types, and specifically is implemented by standard POJO serializer (BeanSerializer). It is usually not needed for container types as their type definitions are not cyclic, unlike some POJO types.
  2. createContextual(tools.jackson.databind.SerializationContext, tools.jackson.databind.BeanProperty): called on resolved instance (whether newly created, or found via cache), when serializer is to be used for specific property, or as root value serializer (no referring property). It is used to apply annotations from property accessors (getter, field), and may also be used for resolving nested types for container serializers (such as ones for Collections).
Caching of serializers occurs after resolve(tools.jackson.databind.SerializationContext) is called: cached instances are not contextual.

NOTE: various serialize methods are never (to be) called with null values -- caller must handle null values, usually by calling SerializationContext.findNullValueSerializer(tools.jackson.databind.BeanProperty) to obtain serializer to use. This also means that custom serializers cannot be directly used to change the output to produce when serializing null values.

NOTE: In Jackson 2.x was named JsonSerializer

  • Constructor Details

    • ValueSerializer

      public ValueSerializer()

  • Method Details

    • resolve

      public void resolve(SerializationContext ctxt)
      Method called after SerializationContext has registered the serializer, 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).

      Note that this method does NOT return serializer, since resolution is not allowed to change actual serializer to use.

      Parameters:
      ctxt - Currently active serialization context.

    • createContextual

      public ValueSerializer<?> createContextual(SerializationContext ctxt, BeanProperty property)
      Method called to see if a different (or differently configured) serializer is needed to serialize values of specified property (or, for root values, in which case `null` is passed). 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.

      Note that method is only called once per POJO property, and for the first usage as root value serializer; it is not called for every serialization, as doing that would have significant performance impact; most serializers cache contextual instances for future use.

      Parameters:
      ctxt - Context to use for accessing config, other serializers
      property - Property (defined by one or more accessors - field or method - used for accessing logical property value) for which serializer is used to be used; or, `null` for root value (or in cases where caller does not have this information, which is handled as root value case).
      Returns:
      Serializer to use for serializing values of specified property; may be this instance or a new instance.

    • unwrappingSerializer

      public ValueSerializer<T> unwrappingSerializer(NameTransformer unwrapper)
      Method that will return serializer instance that produces "unwrapped" serialization, if applicable for type being serialized (which is the case for some serializers that produce JSON Objects as output). If no unwrapped serializer can be constructed, will simply return serializer as-is.

      Default implementation just returns serializer as-is, indicating that no unwrapped variant exists

      Parameters:
      unwrapper - Name transformation to use to convert between names of unwrapper properties

    • replaceDelegatee

      public ValueSerializer<T> replaceDelegatee(ValueSerializer<?> delegatee)
      Method that can be called to try to replace serializer this serializer delegates calls to. If not supported (either this serializer 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 serializer as is.

    • withFilterId

      public ValueSerializer<?> withFilterId(Object filterId)
      Mutant factory method that is called if contextual configuration indicates that a specific filter (as specified by filterId) is to be used for serialization.

      Default implementation simply returns this; sub-classes that do support filtering will need to create and return new instance if filter changes.

    • withIgnoredProperties

      public ValueSerializer<?> withIgnoredProperties(Set<String> ignoredProperties)
      Mutant factory method called to create a new instance after excluding specified set of properties by name, if there is any.
      Parameters:
      ignoredProperties - Set of property names to ignore for serialization;
      Returns:
      Serializer instance that without specified set of properties to ignore (if any)

    • withFormatOverrides

      public ValueSerializer<?> withFormatOverrides(SerializationConfig config, JsonFormat.Value formatOverrides)
      Mutant factory called if there is need to create a serializer with specified format overrides (typically from property on which this serializer would be used, based on type declaration). Method is called before createContextual(tools.jackson.databind.SerializationContext, tools.jackson.databind.BeanProperty) but right after serializer is either constructed or fetched from cache.

      Method can do one of three things:

      • Return this instance as is: this means that none of overrides has any effect
      • Return an alternate ValueSerializer, suitable for use with specified format
      • Return null to indicate that this serializer instance is not suitable for handling format variation, but does not know how to construct new serializer: caller will typically then call SerializerFactory with overrides to construct new serializer
      One example of second approach is the case where JsonFormat.Shape.STRING indicates String representation and code can just construct simple "string-like serializer", or variant of itself (similar to how createContextual(tools.jackson.databind.SerializationContext, tools.jackson.databind.BeanProperty) is often implemented). And third case (returning null) is applicable for cases like format defines JsonFormat.Shape.POJO, requesting "introspect serializer for POJO regardless of type": SerializerFactory is needed for full re-introspection, typically.
      Parameters:
      formatOverrides - (not null) Override settings, NOT including original format settings (which serializer needs to explicitly retain if needed)
      Since:
      3.0

    • serialize

      public abstract void serialize(T value, JsonGenerator gen, SerializationContext ctxt) throws JacksonException
      Method that can be called to ask implementation to serialize values of type this serializer handles.
      Parameters:
      value - Value to serialize; can not be null.
      gen - Generator used to output resulting Json content
      ctxt - Context that can be used to get serializers for serializing Objects value contains, if any.
      Throws:
      JacksonException

    • serializeWithType

      public void serializeWithType(T value, JsonGenerator gen, SerializationContext ctxt, TypeSerializer typeSer) throws JacksonException
      Method that can be called to ask implementation to serialize values of type this serializer handles, using specified type serializer for embedding necessary type information.

      Default implementation will throw UnsupportedOperationException to indicate that proper type handling needs to be implemented.

      For simple datatypes written as a single scalar value (JSON String, Number, Boolean), implementation would look like: 

        // note: method to call depends on whether this type is serialized as JSON scalar, object or Array!
  typeSer.writeTypePrefixForScalar(value, gen);
  serialize(value, gen, provider);
  typeSer.writeTypeSuffixForScalar(value, gen);
      and implementations for type serialized as JSON Arrays or Objects would differ slightly, as START-ARRAY/END-ARRAY and START-OBJECT/END-OBJECT pairs need to be properly handled with respect to serializing of contents.
      Parameters:
      value - Value to serialize; can not be null.
      gen - Generator used to output resulting Json content
      ctxt - Context that can be used to get serializers for serializing Objects value contains, if any.
      typeSer - Type serializer to use for including type information
      Throws:
      JacksonException

    • handledType

      public Class<?> handledType()
      Method for accessing type of Objects this serializer can handle. 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).

      NOTE: starting with 3.0, left abstract.

    • usesObjectId

      public boolean usesObjectId()
      Method that can be called to see whether this serializer instance will use Object Id to handle cyclic references.

    • isUnwrappingSerializer

      public boolean isUnwrappingSerializer()
      Accessor for checking whether this serializer is an "unwrapping" serializer; this is necessary to know since it may also require caller to suppress writing of the leading property name.

    • getDelegatee

      public ValueSerializer<?> getDelegatee()
      Accessor that can be used to determine if this serializer uses another serializer for actual serialization, by delegating calls. If so, will return immediate delegate (which itself may delegate to further serializers); otherwise will return null.
      Returns:
      Serializer this serializer delegates calls to, if null; null otherwise.

    • properties

      public Iterator<PropertyWriter> properties()
      Accessor for iterating over logical properties that the type handled by this serializer has, from serialization perspective. Actual type of properties, if any, will be BeanPropertyWriter. Of standard Jackson serializers, only BeanSerializer exposes properties.

    • isEmpty

      public boolean isEmpty(SerializationContext ctxt, T value)
      Method called to check whether given serializable value is considered "empty" value (for purposes of suppressing serialization of empty values).

      Default implementation will consider only null values to be empty.

    • acceptJsonFormatVisitor

      public void acceptJsonFormatVisitor(JsonFormatVisitorWrapper visitor, JavaType type)
      Default implementation simply calls JsonFormatVisitorWrapper.expectAnyFormat(JavaType).
      Specified by:
      acceptJsonFormatVisitor in interface JsonFormatVisitable
      type - Type of element (entity like property) being visited