Gson - how to parse dynamic JSON string with nested JSON?

Question

I have JSON string with dynamic elements, till now I parse it into Map:

Map map = new Gson().fromJson(jsonString, 
        new TypeToken<HashMap<String, String>>() {}.getType());

Now I need to solve thsi situation - one of these dynamic variables could be another JSON string.

Do you have some advice ho to solve it? Thanks in advance.

EDIT: JSON string example added (formatted):

{
    "key1": "val1",
    "key2": "val2",
    "key3": {
        "subkey1": [
            "subvalue1",
            "subvalue1"
        ],
        "subkey‌2": [
            "subvalue2"
        ]
    },
    "key4": "val3"
}

Eg: {"key1":"val1","key2":"val2","key3": {"subkey1":"subvalue1","subkey2":"subvalue2"},"key4":"val3"} but I don't a structure of this JSON, so I don't know if is there some nested json and if so, I don't know its structure. — jnemecz
– jnemecz, Commented Aug 31, 2012 at 12:02
Yes, there is an exception: Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_ARRAY at line 1 column 57 — jnemecz
– jnemecz, Commented Aug 31, 2012 at 12:03
According to this other question I found that should occur if your json-data is invalid (with a [ in that case), but off the bat I can't see anything wrong with the json you posted. — Aske B.
– Aske B., Commented Aug 31, 2012 at 12:13
Its weird, I'll check the structure but the JSON string is generated via PHP function json_encode() (php.net/manual/en/function.json-encode.php). Thanks for now. — jnemecz
– jnemecz, Commented Aug 31, 2012 at 12:15

Marek Dec · Accepted Answer · 2012-08-31 13:02:12Z

3

What you call another JSON string is just a json object. Change the Map value type to Object from String: TypeToken>

String jsonString = "{\"key1\":\"val1\",\"key2\":\"val2\",\"key3\": {\"subkey1\":\"subvalue1\",\"subkey2\":\"subvalue2\"},\"key4\":\"val3\"}";

Map<String, Object> map = new Gson().fromJson(jsonString, new TypeToken<Map<String, Object>>() {
}.getType());

The above example works with GSON 2.2.2. And sysout(map) produces

{key1=val1, key2=val2, key3={subkey1=subvalue1, subkey2=subvalue2}, key4=val3}

As a small improvement I'd suggest that you explicitly specify map type parameters, and use Map instead of HashMap for the TypeToken.

answered Aug 31, 2012 at 13:02

Marek Dec

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3 Comments

jnemecz Over a year ago

Yes, now it works, thank you. I loop through parsed Objects in Map and I am processing them - is there some way how to solve out if Object is another Map and not string value?

Marek Dec Over a year ago

@user1315357 There are obviously ways to solve it. The question is what you want to do with it. You can test if a value is a Map using the instanceof parameter. For example you could create some recursive method that prints out a value if it is a string or iterates over the values if it is a Map and recursively calls itself for every one of them. If you consider this question answered, could you accept it please?

jnemecz Over a year ago

It doesn't work with this JSON: {"key1":"val1","key2":"val2","key3":{"subkey1":["subvalue1","subvalue1"],"subkey2":["subvalue2"]},"key4":"val3"} created by this PHP code (notice that subkey1 and subkey2 is an array and not a single value as before):

$foo = array(); $foo["key1"] = 'val1'; $foo["key2"] = 'val2'; $foo["key3"] = array('subkey1'=>array('subvalue1','subvalue1'),'subkey2'=>array('subvalue2')); $foo["key4"] = 'val3'; var_dump(json_encode($foo));

"doesn't work" mean that this nested JSON object is not parsed and is returned as a String.

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