Can not deserialize instance of java.util.ArrayList out of START_OBJECT token

This error is usually encountered when trying to parse a JSON string that does not start with a JSON array, but rather a JSON object.

For example, if you have a JSON string like this:

{
  "name": "John",
  "age": 30,
  "city": "New York"
}

And you try to parse it using a method that expects a JSON array, such as new Gson().fromJson(jsonString, new TypeToken<ArrayList<YourClass>>(){}.getType()), you will get the "Can not deserialize instance of java.util.ArrayList out of START_OBJECT token" error.

To fix this error, ensure the Java target type matches the JSON structure. Note that wrapping the JSON in brackets changes the data structure, which may not always be the desired fix. If the API actually returns a single object, adjust your DTO to deserialize into a single class instead:

YourClass obj = new Gson().fromJson(jsonString, YourClass.class);

If the API does return an array, format the JSON accordingly and use TypeToken to properly handle generic types:

[
  { "name": "John", "age": 30, "city": "New York" },
  { "name": "Jane", "age": 25, "city": "San Francisco" }
]

ArrayList<YourClass> list = new Gson().fromJson(jsonString, new TypeToken<ArrayList<YourClass>>(){}.getType());