I’m checking if an object in a JSON string exists using this:
JSONObject json = null;
try {
json = new JSONObject(myJsonString);
} catch (JSONException e) { e.printStackTrace(); }
if(json.has("myObject")) System.out.println("EXISTS");
else System.out.println("DOESN'T EXIST");
The problem appears when I attempt to check if a sub object exists. e.g:
...,"queue":{"building":{"q0":{"id":177779,...
Queue always exists and building also, but q0 is not always there. So, how can I check the existence of q0? And, is there a way to check it using the Gson library?
Thank you in advance!
You can simply give it a try and return null if the try failed. Or you can break your attempt up into little pieces to monitor where it fails.
/**
* This method will return the JSONObject q0, if it exists
* If it doesn't exist it will return NULL
*
*/
private JSONObject getQZero(JSONObject json)
{
try
{
return json.getJSONObject("queue").getJSONObject("building").getJSONObject("q0");
}
catch (JSONException e)
{
// This could be triggered either because there is no q0
// or because the JSON structure is different from what was expected.
return null;
}
}
You could also go step by step, if you want to print logs for each level;
/**
* This method will show where your jsonparsing fails.
* It will throw a JSONOException if the json is way different from what
* was expected, and otherwise it will print a log of where the parsing
* failed.
*/
private JSONObject getQZero(JSONObject json) throws JSONException
{
// Stop if no queue
if (! myObject.has("queue")
{
Log.d(TAG, "no queue!");
return null;
}
JSONObject queue = myObject.getJSONObject("queue");
// Stop if no building
if (! queue.has("building")
{
Log.d(TAG, "no building!");
return null;
}
JSONObject building = queue.getJSONObject("building")
// Stop if no q0
if (! building.has("q0"))
{
Log.d(TAG, "no q0!");
return null;
}
JSONObject q0 = building.getJSONObject("q0");
// Q0 is returned here. If the method returned earlier, it returned NULL
// You could also do nested ifs, but the indentation gets crazy
return q0;
}
Answer：
Use the exceptions to your advantage
try {
JSONObject i = json. getJSONObject("q0");
// Is there do something
} catch (JSONException e) {
// Isn't there
}
http://www.json.org/javadoc/org/json/JSONObject.html#getJSONObject(java.lang.String)
JSONException – if the key is not found or if the value is not a JSONObject.
Tags: androidandroid, json, object
