public final class RuntimeTypeAdapterFactory<T> extends Object implements com.google.gson.TypeAdapterFactory
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.
RuntimeTypeAdapterFactory
by passing the base type and type field
name to the of(java.lang.Class<T>, java.lang.String)
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.
shapeAdapter.registerSubtype(Rectangle.class, "Rectangle");
shapeAdapter.registerSubtype(Circle.class, "Circle");
shapeAdapter.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);
Modifier and Type | Method and Description |
---|---|
<R> com.google.gson.TypeAdapter<R> |
create(com.google.gson.Gson gson,
com.google.gson.reflect.TypeToken<R> type) |
static <T> RuntimeTypeAdapterFactory<T> |
of(Class<T> baseType) |
static <T> RuntimeTypeAdapterFactory<T> |
of(Class<T> baseType,
String typeFieldName) |
RuntimeTypeAdapterFactory<T> |
registerSubtype(Class<? extends T> type) |
RuntimeTypeAdapterFactory<T> |
registerSubtype(Class<? extends T> type,
String label) |
public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName)
public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType)
public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type, String label)
public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type)
public <R> com.google.gson.TypeAdapter<R> create(com.google.gson.Gson gson, com.google.gson.reflect.TypeToken<R> type)
create
in interface com.google.gson.TypeAdapterFactory
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