Package com.google.gson.typeadapters
Class RuntimeTypeAdapterFactory<T>
java.lang.Object
com.google.gson.typeadapters.RuntimeTypeAdapterFactory<T>
- All Implemented Interfaces:
TypeAdapterFactory
Adapts values whose runtime type may differ from their declaration type. This
is necessary when a field's type is not the same type that GSON should create
when deserializing that field. For example, consider these types:
abstract class Shape {
int x;
int y;
}
class Circle extends Shape {
int radius;
}
class Rectangle extends Shape {
int width;
int height;
}
class Diamond extends Shape {
int width;
int height;
}
class Drawing {
Shape bottomShape;
Shape topShape;
}
Without additional type information, the serialized JSON is ambiguous. Is the bottom shape in this drawing a rectangle or a diamond?
{
"bottomShape": {
"width": 10,
"height": 5,
"x": 0,
"y": 0
},
"topShape": {
"radius": 2,
"x": 4,
"y": 1
}
}
This class addresses this problem by adding type information to the
serialized JSON and honoring that type information when the JSON is
deserialized:
{
"bottomShape": {
"type": "Diamond",
"width": 10,
"height": 5,
"x": 0,
"y": 0
},
"topShape": {
"type": "Circle",
"radius": 2,
"x": 4,
"y": 1
}
}
Both the type field name ("type"
) and the type labels (
"Rectangle"
) are configurable.
Registering Types
Create aRuntimeTypeAdapterFactory
by passing the base type and type field
name to the of(java.lang.Class<T>, java.lang.String, boolean)
factory method. If you don't supply an explicit type
field name, "type"
will be used.
RuntimeTypeAdapterFactory<Shape> shapeAdapterFactory
= RuntimeTypeAdapterFactory.of(Shape.class, "type");
Next register all of your subtypes. Every subtype must be explicitly
registered. This protects your application from injection attacks. If you
don't supply an explicit type label, the type's simple name will be used.
shapeAdapterFactory.registerSubtype(Rectangle.class, "Rectangle");
shapeAdapterFactory.registerSubtype(Circle.class, "Circle");
shapeAdapterFactory.registerSubtype(Diamond.class, "Diamond");
Finally, register the type adapter factory in your application's GSON builder:
Gson gson = new GsonBuilder()
.registerTypeAdapterFactory(shapeAdapterFactory)
.create();
Like GsonBuilder
, this API supports chaining:
RuntimeTypeAdapterFactory<Shape> shapeAdapterFactory = RuntimeTypeAdapterFactory.of(Shape.class)
.registerSubtype(Rectangle.class)
.registerSubtype(Circle.class)
.registerSubtype(Diamond.class);
Serialization and deserialization
In order to serialize and deserialize a polymorphic object, you must specify the base type explicitly.
Diamond diamond = new Diamond();
String json = gson.toJson(diamond, Shape.class);
And then:
Shape shape = gson.fromJson(json, Shape.class);
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Field Summary
Fields -
Constructor Summary
ConstructorsModifierConstructorDescriptionprivate
RuntimeTypeAdapterFactory
(Class<?> baseType, String typeFieldName, boolean maintainType) -
Method Summary
Modifier and TypeMethodDescription<R> TypeAdapter
<R> Returns a type adapter fortype
, or null if this factory doesn't supporttype
.static <T> RuntimeTypeAdapterFactory
<T> Creates a new runtime type adapter forbaseType
using"type"
as the type field name.static <T> RuntimeTypeAdapterFactory
<T> Creates a new runtime type adapter using forbaseType
usingtypeFieldName
as the type field name.static <T> RuntimeTypeAdapterFactory
<T> Creates a new runtime type adapter using forbaseType
usingtypeFieldName
as the type field name.Ensures that this factory will handle not just the givenbaseType
, but any subtype of that type.registerSubtype
(Class<? extends T> type) Registerstype
identified by itssimple name
.registerSubtype
(Class<? extends T> type, String label) Registerstype
identified bylabel
.
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Field Details
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baseType
-
typeFieldName
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labelToSubtype
-
subtypeToLabel
-
maintainType
private final boolean maintainType -
recognizeSubtypes
private boolean recognizeSubtypes
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Constructor Details
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RuntimeTypeAdapterFactory
-
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Method Details
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of
public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName, boolean maintainType) Creates a new runtime type adapter using forbaseType
usingtypeFieldName
as the type field name. Type field names are case sensitive.- Parameters:
maintainType
- true if the type field should be included in deserialized objects
-
of
Creates a new runtime type adapter using forbaseType
usingtypeFieldName
as the type field name. Type field names are case sensitive. -
of
Creates a new runtime type adapter forbaseType
using"type"
as the type field name. -
recognizeSubtypes
Ensures that this factory will handle not just the givenbaseType
, but any subtype of that type. -
registerSubtype
Registerstype
identified bylabel
. Labels are case sensitive.- Throws:
IllegalArgumentException
- if eithertype
orlabel
have already been registered on this type adapter.
-
registerSubtype
Registerstype
identified by itssimple name
. Labels are case sensitive.- Throws:
IllegalArgumentException
- if eithertype
or its simple name have already been registered on this type adapter.
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create
Description copied from interface:TypeAdapterFactory
Returns a type adapter fortype
, or null if this factory doesn't supporttype
.- Specified by:
create
in interfaceTypeAdapterFactory
-