Gson Is there an easier way to serialize a map

Question

This link from the Gson project seems to indicate that I would have to do something like the following for serializing a typed Map to JSON       public static class NumberTypeAdapter        implements JsonSerializer lt Number gt   JsonDeserializer lt Number gt   InstanceCreator lt Number gt         public JsonElement serialize Number src  Type typeOfSrc  JsonSerializationContext context          return new JsonPrimitive src              public Number deserialize JsonElement json  Type typeOfT  JsonDeserializationContext context          throws JsonParseException         JsonPrimitive jsonPrimitive   json getAsJsonPrimitive          if  jsonPrimitive isNumber              return jsonPrimitive getAsNumber            else           throw new IllegalStateException  Expected a number field  but was     json                      public Number createInstance Type type          return 1L               public static void main String   args        Map lt String  Number gt  map   new HashMap lt String  Number gt             map put  int   123       map put  long   1234567890123456789L       map put  double   1234 5678D       map put  float   1 2345F       Type mapType   new TypeToken lt Map lt String  Number gt  gt       getType         Gson gson   new GsonBuilder   registerTypeAdapter Number class  new NumberTypeAdapter    create        String json   gson toJson map  mapType       System out println json        Map lt String  Number gt  deserializedMap   gson fromJson json  mapType       System out println deserializedMap         Cool and that works  but it seems like so much overhead  a whole Type Adapter class    I have used other JSON libraries like JSONLib and they let you build a map in the following way   JSONObject json   new JSONObject    for Entry lt String Integer gt  entry   map entrySet          json put entry getKey    entry getValue         Or if I have a custom class something like the following   JSONObject json   new JSONObject    for Entry lt String MyClass gt  entry   map entrySet      JSONObject myClassJson    JSONObject fromObject entry getValue          json put entry getKey    myClassJson       The process is more manual  but requires way less code and doesn t have the overhead of haivng to create a custom Type Adapter for Number or in most cases for my own custom class   Is this the only way to serialize a map with Gson  or has anyone found a way that beats out what Gson recommends in the link above

User · Answer

Map lt String  Object gt  config   gson fromJson reader  Map class

User · Answer

Only the TypeToken part is neccesary  when there are Generics involved    Map lt String  String gt  myMap   new HashMap lt String  String gt     myMap put  one    hello    myMap put  two    world     Gson gson   new GsonBuilder   create    String json   gson toJson myMap    System out println json    Type typeOfHashMap   new TypeToken lt Map lt String  String gt  gt        getType    Map lt String  String gt  newMap   gson fromJson json  typeOfHashMap      This type must match TypeToken System out println newMap get  one     System out println newMap get  two       Output     two   world   one   hello   hello world

User · Answer

I m pretty sure GSON serializes deserializes Maps and multiple-nested Maps  i e  Map lt String  Map lt String  Object gt  gt   just fine by default  The example provided I believe is nothing more than just a starting point if you need to do something more complex   Check out the MapTypeAdapterFactory class in the GSON source  http   code google com p google-gson source browse trunk gson src main java com google gson internal bind MapTypeAdapterFactory java  So long as the types of the keys and values can be serialized into JSON strings  and you can create your own serializers deserializers for these custom objects  you shouldn t have any issues

User · Answer

Default  The default Gson implementation of Map serialization uses toString   on the key   Gson gson   new GsonBuilder            setPrettyPrinting   create    Map lt Point  String gt  original   new HashMap lt  gt     original put new Point 1  2    a    original put new Point 3  4    b    System out println gson toJson original      Will give        java awt Point x u003d1 y u003d2     a      java awt Point x u003d3 y u003d4     b        Using enableComplexMapKeySerialization  If you want the Map Key to be serialized according to default Gson rules you can use enableComplexMapKeySerialization  This will return an array of arrays of key-value pairs   Gson gson   new GsonBuilder   enableComplexMapKeySerialization            setPrettyPrinting   create    Map lt Point  String gt  original   new HashMap lt  gt     original put new Point 1  2    a    original put new Point 3  4    b    System out println gson toJson original      Will return                      x   1         y   2             a                        x   3         y   4             b          More details can be found here

User · Answer

In Gson 2 7 2 it s as easy as   Gson gson   new Gson    String serialized   gson toJson map

[java] Gson: Is there an easier way to serialize a map

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