com.google.gson.internal.bind

类 MapTypeAdapterFactory

java.lang.Object

com.google.gson.internal.bind.MapTypeAdapterFactory

所有已实现的接口:

TypeAdapterFactory

public final class MapTypeAdapterFactory
extends Object
implements TypeAdapterFactory

Adapts maps to either JSON objects or JSON arrays.

Maps as JSON objects

For primitive keys or when complex map key serialization is not enabled, this converts Java Maps to JSON Objects. This requires that map keys can be serialized as strings; this is insufficient for some key types. For example, consider a map whose keys are points on a grid. The default JSON form encodes reasonably:

   Map<Point, String> original = new LinkedHashMap<Point, String>();
   original.put(new Point(5, 6), "a");
   original.put(new Point(8, 8), "b");
   System.out.println(gson.toJson(original, type));
 

The above code prints this JSON object:

   {
     "(5,6)": "a",
     "(8,8)": "b"
   }
 

But GSON is unable to deserialize this value because the JSON string name is just the toString() of the map key. Attempting to convert the above JSON to an object fails with a parse exception:

com.google.gson.JsonParseException: Expecting object found: "(5,6)"
   at com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler
   at com.google.gson.ObjectNavigator.navigateClassFields
   ...

Maps as JSON arrays

An alternative approach taken by this type adapter when it is required and complex map key serialization is enabled is to encode maps as arrays of map entries. Each map entry is a two element array containing a key and a value. This approach is more flexible because any type can be used as the map's key; not just strings. But it's also less portable because the receiver of such JSON must be aware of the map entry convention.

Register this adapter when you are creating your GSON instance.

   Gson gson = new GsonBuilder()
     .registerTypeAdapter(Map.class, new MapAsArrayTypeAdapter())
     .create();
 

This will change the structure of the JSON emitted by the code above. Now we get an array. In this case the arrays elements are map entries:

   [
     [
       {
         "x": 5,
         "y": 6
       },
       "a",
     ],
     [
       {
         "x": 8,
         "y": 8
       },
       "b"
     ]
   ]
 

This format will serialize and deserialize just fine as long as this adapter is registered.

构造器概要

构造器

构造器和说明
MapTypeAdapterFactory(ConstructorConstructor constructorConstructor, boolean complexMapKeySerialization)

方法概要

方法

限定符和类型	方法和说明
<T> TypeAdapter<T>	create(Gson gson, TypeToken<T> typeToken) Returns a type adapter for type, or null if this factory doesn't support type.

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

构造器详细资料

MapTypeAdapterFactory

public MapTypeAdapterFactory(ConstructorConstructor constructorConstructor,
                     boolean complexMapKeySerialization)

方法详细资料

create

public <T> TypeAdapter<T> create(Gson gson,
                        TypeToken<T> typeToken)

从接口复制的说明: TypeAdapterFactory

Returns a type adapter for type, or null if this factory doesn't support type.

指定者:

create 在接口中 TypeAdapterFactory