Class RuntimeTypeAdapterFactory<T>

  • All Implemented Interfaces:
    com.google.gson.TypeAdapterFactory

    public final class RuntimeTypeAdapterFactory<T>
    extends java.lang.Object
    implements com.google.gson.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 a 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);
     
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method 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​(java.lang.Class<T> baseType)
      Creates a new runtime type adapter for baseType using "type" as the type field name.
      static <T> RuntimeTypeAdapterFactory<T> of​(java.lang.Class<T> baseType, java.lang.String typeFieldName)
      Creates a new runtime type adapter using for baseType using typeFieldName as the type field name.
      RuntimeTypeAdapterFactory<T> registerSubtype​(java.lang.Class<? extends T> type)
      Registers type identified by its simple name.
      RuntimeTypeAdapterFactory<T> registerSubtype​(java.lang.Class<? extends T> type, java.lang.String label)
      Registers type identified by label.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Method Detail

      • of

        public static <T> RuntimeTypeAdapterFactory<T> of​(java.lang.Class<T> baseType,
                                                          java.lang.String typeFieldName)
        Creates a new runtime type adapter using for baseType using typeFieldName as the type field name. Type field names are case sensitive.
      • of

        public static <T> RuntimeTypeAdapterFactory<T> of​(java.lang.Class<T> baseType)
        Creates a new runtime type adapter for baseType using "type" as the type field name.
      • registerSubtype

        public RuntimeTypeAdapterFactory<T> registerSubtype​(java.lang.Class<? extends T> type,
                                                            java.lang.String label)
        Registers type identified by label. Labels are case sensitive.
        Throws:
        java.lang.IllegalArgumentException - if either type or label have already been registered on this type adapter.
      • registerSubtype

        public RuntimeTypeAdapterFactory<T> registerSubtype​(java.lang.Class<? extends T> type)
        Registers type identified by its simple name. Labels are case sensitive.
        Throws:
        java.lang.IllegalArgumentException - if either type or its simple name have already been registered on this type adapter.
      • create

        public <R> com.google.gson.TypeAdapter<R> create​(com.google.gson.Gson gson,
                                                         com.google.gson.reflect.TypeToken<R> type)
        Specified by:
        create in interface com.google.gson.TypeAdapterFactory