Preventing Gson deserializing JSON String of a List to actual ArrayList

Question

Here is my code

Gson gson = new Gson();
HashMap<String, String> map = new HashMap<>();
map = gson.fromJson(new FileReader(inputFile), map.getClass());

The content of the inputFile is

{
  "key1": "[\"value1\"]",
  "key2": "value2"
}

When I inspect the value of map.get("key2") during debugging in Eclipse, the value is actually (java.util.ArrayList<E>) [value1]

How can I make Gson deserialize the content to

{key1="[value1]", key2=value2}

Thanks

Sotirios Delimanolis · Accepted Answer · 2014-10-01 23:49:00Z

1

I feel like you are seeing the HashMap#toString() output of

{key1=["value1"], key2=value2}

and thinking that

["value1"]

is a List of some type, containing a String value of "value1".

It isn't. Your String, as a String literal, would be represented as "[\"value1\"]". Its value is ["value1"]. That's what gets displayed.

Both your JSON key-value entries are string-string and will get converted as such.

"key1": "[\"value1\"]",
//      ^ indicates a JSON string

edited Oct 1, 2014 at 23:49

answered Oct 1, 2014 at 23:24

Sotirios Delimanolis

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2 Comments

derrdji Over a year ago

The test code snippet I tried also worked, regardless of loading the source String from file or variable in memory. The complete case is I have some other code that down loads the file from S3 and return me a File object. I would get this deserialization error if I do not write the File to a local file. After writing the file locally and reopening the local file with FileReader and passing it to the fromJson method, everything is working as expected.

Sotirios Delimanolis Over a year ago

@derrdji So was it just an interpretation problem or something else?

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