Gson: how should i convert a map to json String with gson

[wykCN]

My code likes:

    @Test
    public void testGsonTransferMap(){
        HashMap<String, Object> map = new HashMap<String, Object>() {{
            put("Request", new HashMap<String ,Object>(){{
                put("Data",new HashMap<String,Object>(){{
                    put("NWExID", "7019");
                    put("OrgOrderNo", "123");
                    put("OrgTransDate", "20170518");
                }});
            }});
        }};
        Gson gson = new Gson();
        Type gsonType = new TypeToken<HashMap<String ,Object>>(){}.getType();
        String gsonString = gson.toJson(map,gsonType);
        System.out.println(gsonString);
    } 

and the output is : "{}"
so,what's wrong with my code , how should i do.

[NightlyNexus]

You are trying to serialize an anonymous inner class. Don't.

[henrik242]

All other json implementations I can find seems to handle this well, while new Gson().toJson() returns null when I give it an one-liner map:

Map map = new HashMap() {{ put("hei", "sann"); }};
new Gson().toJson(map);  // returns null!

Other implementations works as expected:

new JSONObject(map).toString();             // returns {"hei":"sann"}
JsonOutput.toJson(map);                     // returns {"hei":"sann"}
new ObjectMapper().writeValueAsString(map); // returns {"hei":"sann"}

It works if I wrap the map:

new Gson().toJson(new HashMap(map));  // returns {"hei":"sann"}

A regular map works too:

map = new HashMap();
map.put("hei", "sann");
new Gson().toJson(map);  // returns {"hei":"sann"}

Is this an expected Gson feature, @NightlyNexus ?

I've created a test project at https://github.com/henrik242/map2json

[JakeWharton]

Yes. This is working as intended.

[codethinker09]

This has been fixed in Gson new version, tested with gson-2.8.5.jar

[ebuildy]

what about to throw exception if anonymous inner class? (instead of returning just "null")

[fpemud]

Running @wykCN's code with gson-2.8.5.jar (under openjdk-1.8) still returns "{}".
Using anonymous inner class is convinent and elegant, why gson doesn't support it?