Why the put method of a JSONObject throws JSONException?

Question

I found few answers here on how to handle this exception, but there was no explanation why would this happen in the first place. I have the following code:

for (Map.Entry<String, Double> entry: qosMap.entrySet()) {
        JSONObject qosEntry = new JSONObject();
        try {
            qosEntry.put(entry.getKey(), entry.getValue());
        } catch (JSONException ex) {
            Logger.getLogger(JSONUtil.class.getName()).log(Level.SEVERE, null, ex);
        }
}

The qosMap will never be empty, and the data in this map will always be valid.

What would be a case where the exception would thrown? Why do I need to have this extra code?

Answer 1

check java docs

"If a value is a non-finite number or if a name is duplicated."

https://docs.oracle.com/middleware/maf222/mobile/api-ref/oracle/adfmf/json/JSONObject.html

Answer 2

Assuming that you are using JSONObject from org.json

org.json.JSONObject.put(String, double) : JSONObject

It puts a key/double pair in the JSONObject.

Parameters:

key: A key string. value: A double which is the value.

Returns: this

Throws:

JSONException If the key is null or if the number is invalid.

I know that the data is always valid. why do I need to have this extra code?

You could make the method throws the exception, as you don't like clutter up your code and also it seems you can't do anything useful by catching the exception either.

It is obvious that you know the data you passed is valid. However the library won't know. That's why it's throwing an checked exception just to let you know in case it fails.

Answer 3

For all types T, JSONObject.put(String key, T value) throws a JSONException when the key is null or the value is a non-finite #. For type double, a JSONException is also thrown if the double value is invalid. See:

https://docs.oracle.com/middleware/maf222/mobile/api-ref/oracle/adfmf/json/JSONObject.html https://developer.android.com/reference/org/json/JSONObject.html