使用GSON解析json对象与json数组

Question

I have a JSON that is either a single object or an array of the same object. Is there a way to parse this data using Gson where it'll distinguish between the single object vs the array?

The only solution I currently have for this is to manually parse the json and surround that with a try catch. First I'll try parsing it as a single object, if it fails, it'll throw an exception and then I'll try to parse it as an array.

I don't want to parse it manually though...that would take me forever. Here's an idea of what's happening.

public class ObjectA implements Serializable{

    public String variable;
    public ObjectB[] objectb; //or ObjectB objectb;

    public ObjectA (){}
}

Here's the object that can either be an array or a single object.

public class ObjectB implements Serializable{

    public String variable1;
    public String variable2;

    public ObjectB (){}
}

And then when interacting with the json response. I'm doing this.

Gson gson = new Gson();
ObjectA[] objectList = gson.fromJson(response, ObjectA[].class);

When the array of ObjectA's are being serialized, the json contains either an array or single object for ObjectB.

[
    {
        "variable": "blah blah",
        "objectb": {
            "variable1": "1",
            "variable2": "2"
        }
    },
    {
        "variable": "blah blah",
        "objectb": {
            "variable1": "1",
            "variable2": "2"
        }
    },
    {
        "variable": "blah blah",
        "objectb": [
            {
                "variable1": "1",
                "variable2": "2"
            },
            {
                "variable1": "1",
                "variable2": "2"
            }
        ]
    }
]

Answer 1

I just changed ObjectB[] to List<ObjectB> into ObjectA declaration.

ArrayList<ObjectA> la = new ArrayList<ObjectA>();
List<ObjectA> list = new Gson().fromJson(json, la.getClass());

for (Object a : list)
{
   System.out.println(a);
}

and this is my result:

{variable=blah blah, objectb={variable1=1, variable2=2}}
{variable=blah blah, objectb={variable1=1, variable2=2}}
{variable=blah blah, objectb=[{variable1=1, variable2=2}, {variable1=1, variable2=2}]}

I think that in full generics era, if you do not have particular needs, you can switch from arrays to lists, you have many benefits that Gson also can use to do a flexible parsing.

Answer 2

Try to use com.google.gson.JsonParser.

        String jsonString = "object json representation";
        JsonParser jsonParser = new JsonParser();
        JsonElement jsonElement = jsonParser.parse(jsonString);

        if (jsonElement.isJsonArray()) {
            // some logic
        }

There are different ways to get your object using the JsonElement instance, for example - simply using the com.google.gson.Gson methods :

public <T>  T fromJson(com.google.gson.JsonElement json, java.lang.Class<T> classOfT) throws com.google.gson.JsonSyntaxException 

public <T>  T fromJson(com.google.gson.JsonElement json, java.lang.reflect.Type typeOfT) throws com.google.gson.JsonSyntaxException

So, study the JsonElement, JsonArray, JsonPrimitive, JsonNull and JsonObject classes. Believe, they have an adequate interface to recover your object.

Answer 3

Can you try/catch it by first trying to parse the array, then falling back to parsing the single object class?

You could also do a real simple test and look to the first non whitespace character in the string you are deseralizing, if it is a "{" it is a single object, if it is a "[" it is an array