解析复杂的JSON文件

Question

I need to parse a JSON file and put the data into a HTML table. I am using GWT for this application, the data shall be read from the file on the server side and passed to the client on page load.

The format for the JSONObjects in the file are as follows:

{  
"Object 1": [
{ "value1": [ "subKey1", "subValue2" ], "value2": "val", "value3": { "key1": val1, "key2": val2, "key3": val3} },
{ "value2": [ "subKey1", "subValue2" ], "value2": "val", "value3": { "key1": val1, "key2": val2, "key3": val3} },
....
....
],

"Object 2": [
{ "value1": [ "subKey1", "subValue2" ], "value2": "val", "value3": { "key1": val1, "key2": val2, "key3": val3} },
{ "value2": [ "subKey1", "subValue2" ], "value2": "val", "value3": { "key1": val1, "key2": val2, "key3": val3} },
....
....
],
 ....

}

Up until now, I have only done simple JSON parsing. The problem I am having here is that the data I am working with has a unique name for each object so I cannot seem to parse them into an array of JSONObjects.

I have attempted to parse them (using JSON simple) this way but I am throwing an error.

    try {
        JSONParser parser = new JSONParser();
        JSONObject obj;
            obj = (JSONObject) parser.parse(new FileReader("file.json"));

        JSONArray array = new JSONArray();
        array.add(obj.get("Object1"));
        array.add(obj.get("Object2"));
        array.add(obj.get("Object3"));
        array.add(obj.get("Object4"));

        JSONObject jo;

        for (Object o : array) {
            jo = (JSONObject) o;
        }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } 

But this throws an error:

    org.json.simple.JSONArray cannot be cast to org.json.simple.JSONObject

Another method from my understanding is to create a POJO class for the objects but since each JSONObject has a different identifier, does that mean each object must have its own unique class? Some JSON2Java methods I have used just create a new class for each of them.

Answer 1

You can check the instance of the Object before casting it:

for (Object obj : array) {
    if (obj instanceof JSONArray) {
       // It's an array
       yourJsonArray = (JSONArray)obj;
    } else if (obj instanceof JSONObject) {
       // It's an object
       yourJsonObject = (JSONObject)obj;
    } else {
       // It's string, number...
    }
 }