Gson之TypeAdapterFactory

在Gson之TypeAdapter的工作原理分析(1) 中分析了一下TypeAdapter的原理：先把TypeAdapter封装成TypeAdapterFactory然后通过TypeAdapterFactory的create创建TypeAdapter使用。在Gson中其实充斥了大量的TypeAdapterFactory,比如基本类型的TypeAdapter都有一个TypeAdapterFactory：

  public static final TypeAdapterFactory BYTE_FACTORY
      = newFactory(byte.class, Byte.class, BYTE);

 public static final TypeAdapterFactory BOOLEAN_FACTORY
      = newFactory(boolean.class, Boolean.class, BOOLEAN);

 public static final TypeAdapterFactory SHORT_FACTORY
      = newFactory(short.class, Short.class, SHORT);
    //等等，还有其他的一些TypeAdapterFactory就不一一列举

 public static  TypeAdapterFactory newFactory(final Class unboxed, final Class boxed, final  TypeAdapter>emptyMap(), false, false, DEFAULT_JSON_NON_EXECUTABLE,
        true, false, false, LongSerializationPolicy.DEFAULT,
        Collections.emptyList());
  }

带有参数的构造器的的其中一个作用就是为Gson对象的List factories 添加大量的Gson自定义的TypeAdapterFactory:

 factories.addAll(typeAdapterFactories);

    // type adapters for basic platform types
    factories.add(TypeAdapters.STRING_FACTORY);
    factories.add(TypeAdapters.INTEGER_FACTORY);
    factories.add(TypeAdapters.BOOLEAN_FACTORY);
    factories.add(TypeAdapters.BYTE_FACTORY);
    factories.add(TypeAdapters.SHORT_FACTORY);
    factories.add(TypeAdapters.newFactory(long.class, Long.class,
            longAdapter(longSerializationPolicy)));
    factories.add(TypeAdapters.newFactory(double.class, Double.class,
            doubleAdapter(serializeSpecialFloatingPointValues)));
    factories.add(TypeAdapters.newFactory(float.class, Float.class,
            floatAdapter(serializeSpecialFloatingPointValues)));
    factories.add(TypeAdapters.NUMBER_FACTORY);
    factories.add(TypeAdapters.CHARACTER_FACTORY);
    factories.add(TypeAdapters.STRING_BUILDER_FACTORY);
    factories.add(TypeAdapters.STRING_BUFFER_FACTORY);
    factories.add(TypeAdapters.newFactory(BigDecimal.class, TypeAdapters.BIG_DECIMAL));
    factories.add(TypeAdapters.newFactory(BigInteger.class, TypeAdapters.BIG_INTEGER));
    factories.add(TypeAdapters.URL_FACTORY);
    factories.add(TypeAdapters.URI_FACTORY);
    factories.add(TypeAdapters.UUID_FACTORY);
    factories.add(TypeAdapters.LOCALE_FACTORY);
    factories.add(TypeAdapters.INET_ADDRESS_FACTORY);
    factories.add(TypeAdapters.BIT_SET_FACTORY);
    factories.add(DateTypeAdapter.FACTORY);
    factories.add(TypeAdapters.CALENDAR_FACTORY);
    factories.add(TimeTypeAdapter.FACTORY);
    factories.add(SqlDateTypeAdapter.FACTORY);
    factories.add(TypeAdapters.TIMESTAMP_FACTORY);
    factories.add(ArrayTypeAdapter.FACTORY);
    factories.add(TypeAdapters.ENUM_FACTORY);
    factories.add(TypeAdapters.CLASS_FACTORY);

    // type adapters for composite and user-defined types
    factories.add(new CollectionTypeAdapterFactory(constructorConstructor));
    factories.add(new MapTypeAdapterFactory(constructorConstructor, complexMapKeySerialization));
    factories.add(new ReflectiveTypeAdapterFactory(
        constructorConstructor, fieldNamingPolicy, excluder));

    this.factories = Collections.unmodifiableList(factories);

其实你也许有个小疑问，既然自己定义了TypeAdapter为什么还需要添加上面这些Factory,为此我专门修改了一下Gson的构造器：

 public Gson(final Excluder excluder, final FieldNamingStrategy fieldNamingPolicy,
          final Map