HashMap to gson with maps as values

Question

I want to convert HashMap to JSON format using this kind of method:

public String JSObject(Object object) {
        Gson gson = new Gson();
        return gson.toJson(object);
}

But the problem is that when my HashMap has another HashMap as a key in the result I've got nothing in the JSON. Let's say I've got something like this in Java:

put("key", HashMap);

after conversion my JSON looks like this:

"key" : {}

Want I want is obviously some kind of these:

"key" : {
    "key1" : "value1",
    "key2" : "value2"
}

Is this becouse toJson() doesn't support more complicated JSON's ? I think that's more probably me doing something wrong.

@EDIT

This is how I initialize the map:

put("key", new HashMap<String,String>(){{
                put("key1", "value1");
            }};

Possible duplicate of [How to serialize a Map of a Map with GSON?](https://stackoverflow.com/questions/4547739/how-to-serialize-a-map-of-a-map-with-gson) — kennytm, Aug 25 '17 at 07:50
For me it is working good, are you sure, that your map is not empty? — ByeBye, Aug 25 '17 at 07:50
hey, thanks for replies, i edited the question to show how I initialize the map — shurrok, Aug 25 '17 at 07:53

ByeBye · Accepted Answer · 2017-08-25T08:06:19.133

1

With this:

final HashMap<String, String> value = new HashMap<String, String>(){{
    put("key1", "value1");
}};

You are creating new AnonymousInnerClass with instance initializer.

From Gson docs :

Gson can also deserialize static nested classes. However, Gson can not automatically deserialize the pure inner classes since their no-args constructor also need a reference to the containing Object which is not available at the time of deserialization.

Just change you map to not use instance initializer:

final Map<String, String> value = new HashMap<>();
value.put("key", "value");

edited Aug 25 '17 at 08:06

answered Aug 25 '17 at 08:00

ByeBye

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In the other words, I need to improve my method. Am I right? – shurrok Aug 25 '17 at 08:03
Just don't use `instance initializer` because it creates anonymous inner classes which gson cannot serialize – ByeBye Aug 25 '17 at 08:06
Yes, that's the simplest solution. But I'm curious if I can change my `JSObject` method to let me use anonymous class – shurrok Aug 25 '17 at 08:10
This does not look to be the issue. You are talking about *de*serialization while the question is asking about serialization. – user3151902 Aug 25 '17 at 08:32

HashMap to gson with maps as values

1 Answers1