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@Target(value={ANNOTATION_TYPE,TYPE,FIELD,METHOD,PARAMETER}) @Retention(value=RUNTIME) public @interface JsonTypeInfo
Annotation used for configuring details of if and how type information is used with JSON serialization and deserialization, to preserve information about actual class of Object instances. This is necessarily for polymorphic types, and may also be needed to link abstract declared types and matching concrete implementation.
Some examples of typical annotations:
// Include Java class name ("com.myempl.ImplClass") as JSON property "class" @JsonTypeInfo(use=Id.CLASS, include=As.PROPERTY, property="class") // Include logical type name (defined in impl classes) as wrapper; 2 annotations @JsonTypeInfo(use=Id.NAME, include=As.WRAPPER_OBJECT) @JsonSubTypes({com.myemp.Impl1.class, com.myempl.Impl2.class})Alternatively you can also define fully customized type handling by using
@JsonTypeResolver
annotation (from databind package).
This annotation can be used both for types (classes) and properties. If both exist, annotation on property has precedence, as it is considered more specific.
When used for properties (fields, methods), this annotation applies
to values: so when applied to structure types
(like Collection
, Map
, arrays),
will apply to contained values, not the container;
for non-structured types there is no difference.
This is identical to how JAXB handles type information
annotations; and is chosen since it is the dominant use case.
There is no per-property way to force type information to be included
for type of container (structured type); for container types one has
to use annotation for type declaration.
Note on visibility of type identifier: by default, deserialization
(use during reading of JSON) of type identifier
is completely handled by Jackson, and is not passed to
deserializers. However, if so desired,
it is possible to define property visible = true
in which case property will be passed as-is to deserializers
(and set via setter or field) on deserialization.
On serialization side, Jackson will generate type id by itself,
except if there is a property with name that matches
property()
, in which case value of that property is
used instead.
Required Element Summary | |
---|---|
JsonTypeInfo.Id |
use
What kind of type metadata is to be used for serializing and deserializing type information for instances of annotated type (and its subtypes unless overridden) |
Optional Element Summary | |
---|---|
Class<?> |
defaultImpl
Optional property that can be used to specify default implementation class to use if type identifier is either not present, or can not be mapped to a registered type (which can occur for ids, but not when specifying explicit class to use). |
JsonTypeInfo.As |
include
What mechanism is used for including type metadata (if any; for JsonTypeInfo.Id.NONE nothing is included). |
String |
property
Property names used when type inclusion method ( JsonTypeInfo.As.PROPERTY ) is used
(or possibly when using type metadata of type JsonTypeInfo.Id.CUSTOM ). |
boolean |
visible
Property that defines whether type identifier value will be passed as part of JSON stream to deserializer (true), or handled and removed by TypeDeserializer (false). |
Element Detail |
---|
public abstract JsonTypeInfo.Id use
public abstract JsonTypeInfo.As include
JsonTypeInfo.Id.NONE
nothing is included). Default
Note that for type metadata type of JsonTypeInfo.Id.CUSTOM
,
this setting may or may not have any effect.
public abstract String property
JsonTypeInfo.As.PROPERTY
) is used
(or possibly when using type metadata of type JsonTypeInfo.Id.CUSTOM
).
If POJO itself has a property with same name, value of property
will be set with type id metadata: if no such property exists, type id
is only used for determining actual type.
Default property name used if this property is not explicitly defined
(or is set to empty String) is based on
type metadata type (use()
) used.
public abstract Class<?> defaultImpl
Note that while this property allows specification of the default implementation to use, it does not help with structural issues that may arise if type information is missing. This means that most often this is used with type-name -based resolution, to cover cases where new sub-types are added, but base type is not changed to reference new sub-types.
public abstract boolean visible
TypeDeserializer
(false).
Default value is false, meaning that Jackson handles and removes
the type identifier from JSON content that is passed to
JsonDeserializer
.
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