Question

I want to gson and de-gson a hashmap with generics.
I can do it successfully when my key is a string but not if it is an
object.
I have the two code part here . the first doesnt work and the second
does.

// doesnt work works
 try {
       TradableBean tradable = new TradableBean("Tradable");
       PositionBean position = new PositionBean(tradable);
       Map<TradableBean, PositionBean> map1 = new HashMap<TradableBean, PositionBean>();
       map1.put(tradable, position);
       String json1 = gson.toJson(map1);
       Map<TradableBean, PositionBean> map2 = gson.fromJson(json1, new TypeToken<Map<TradableBean, PositionBean>>(){}.getType());
       System.out.println(map2);
   } catch (Exception e) {
       System.out.println("failed");
   }

and now the working part –

 // works - with string
   try {
       String tradable = new String("Tradable");
       PositionBean position = new PositionBean(new TradableBean("Tradable"));
       Map<String, PositionBean> map1 = new HashMap<String,PositionBean>();
       map1.put(tradable, position);
       String json1 = gson.toJson(map1);
       Map<String, PositionBean> map2 = gson.fromJson(json1, new TypeToken<Map<String, PositionBean>>() {}.getType());
       System.out.println(map2);
   } catch (Exception e) {
       System.out.println("failed");
   }

and in the TradableBean I have:

@Override public int hashCode() {
   return getId();} 
@Override public boolean equals(Object obj) {
   boolean equals = false;
   if (obj instanceof AccountBean){
       TradableBean tradable_p = (TradableBean)obj;
       if (getId()==tradable_p.getId()){
           equals = true;
       }
   }
   return equals;

}

the exception:

com.google.gson.JsonParseException: Expecting object found:
"TradableBean{id=0, tradableName='Tradable', moneyMultiplier=1,
expirationDate=null}"
       at
com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler(JsonObjectDeserializationVisitor.java:
100)
       at
com.google.gson.ObjectNavigator.navigateClassFields(ObjectNavigator.java:
150)
       at com.google.gson.ObjectNavigator.accept(ObjectNavigator.java:123)
       at
com.google.gson.JsonDeserializationContextDefault.fromJsonPrimitive(JsonDeserializationContextDefault.java:
84)
       at
com.google.gson.JsonDeserializationContextDefault.deserialize(JsonDeserializationContextDefault.java:
53)
       at com.google.gson.DefaultTypeAdapters
$MapTypeAdapter.deserialize(DefaultTypeAdapters.java:531)
       at com.google.gson.DefaultTypeAdapters
$MapTypeAdapter.deserialize(DefaultTypeAdapters.java:498)
       at
com.google.gson.JsonDeserializerExceptionWrapper.deserialize(JsonDeserializerExceptionWrapper.java:
50)

Answer 1

I think you need to write your own custom serializator.

Update: the tell-tale is the exception:

com.google.gson.JsonParseException: Expecting object found: "TradableBean{id=0, tradableName='Tradable', moneyMultiplier=1, expirationDate=null}"

The prepending string “TradableBean” seems to be written by a serialization that uses some sort of toString(). the Deserialization expected an object of the form {id=0,... }