Test if it is JSONObject or JSONArray

问题:

I have a json stream which can be something like :

{"intervention":      {        "id":"3",               "subject":"dddd",               "details":"dddd",               "beginDate":"2012-03-08T00:00:00+01:00",               "endDate":"2012-03-18T00:00:00+01:00",               "campus":                        {                           "id":"2",                          "name":"paris"                        }     } } 

or something like

{"intervention":             [{               "id":"1",               "subject":"android",               "details":"test",               "beginDate":"2012-03-26T00:00:00+02:00",               "endDate":"2012-04-09T00:00:00+02:00",               "campus":{                         "id":"1",                         "name":"lille"                        }             },      {      "id":"2",              "subject":"lozlzozlo",              "details":"xxx",              "beginDate":"2012-03-14T00:00:00+01:00",              "endDate":"2012-03-18T00:00:00+01:00",              "campus":{                        "id":"1",                        "name":"lille"                       }             }] }    

In my Java code I do the following:

JSONObject json = RestManager.getJSONfromURL(myuri); // retrieve the entire json stream      JSONArray  interventionJsonArray = json.getJSONArray("intervention"); 

In the first case, the above doesn't work because there is only one element in the stream.. How do I check if the stream is an object or an array ?

I tried with json.length() but it didn't work..

Thanks

回答1:

Something like this should do it:

JSONObject json; Object     intervention; JSONArray  interventionJsonArray; JSONObject interventionObject;  json = RestManager.getJSONfromURL(myuri); // retrieve the entire json stream      Object intervention = json.get("intervention"); if (intervention instanceof JSONArray) {     // It's an array     interventionJsonArray = (JSONArray)intervention; } else if (intervention instanceof JSONObject) {     // It's an object     interventionObject = (JSONObject)intervention; } else {     // It's something else, like a string or number } 

This has the advantage of getting the property value from the main JSONObject just once. Since getting the property value involves walking a hash tree or similar, that's useful for performance (for what it's worth).

回答2:

Maybe a check like this?

JSONObject intervention = json.optJSONObject("intervention"); 

This returns a JSONObject or null if the intervention object is not a JSON object. Next, do this:

JSONArray interventions; if(intervention == null)         interventions=jsonObject.optJSONArray("intervention"); 

This will return you an array if it's a valid JSONArray or else it will give null.

回答3:

To make it simple, you can just check first string from server result.

String result = EntityUtils.toString(httpResponse.getEntity()); //this function produce JSON String firstChar = String.valueOf(result.charAt(0));  if (firstChar.equalsIgnoreCase("[")) {     //json array }else{     //json object } 

This trick is just based on String of JSON format {foo : "bar"} (object) or [ {foo : "bar"}, {foo: "bar2"} ] (array)

回答4:

I haven't tryied it, but maybe...

 JsonObject jRoot = RestManager.getJSONfromURL(myuri); // retrieve the entire json stream JsonElement interventionElement = jRoot.get("intervention"); JsonArray interventionList = new JsonArray();  if(interventionElement.isJsonArray()) interventionList.addAll(interventionElement.getAsJsonArray()); else interventionList.add(interventionElement); 

If it's a JsonArray object, just use getAsJsonArray() to cast it. If not, it's a single element so just add it.

Anyway, your first exemple is broken, you should ask server's owner to fix it. A JSON data structure must be consistent. It's not just because sometime intervention comes with only 1 element that it doesn't need to be an array. If it has only 1 element, it will be an array of only 1 element, but still must be an array, so that clients can parse it using always the same schema.

回答5:

    //returns boolean as true if it is JSONObject else returns boolean false  public static boolean returnBooleanBasedOnJsonObject(Object jsonVal){         boolean h = false;         try {             JSONObject j1=(JSONObject)jsonVal;             h=true;         } catch (Exception e) {             // TODO Auto-generated catch block             e.printStackTrace();    if(e.toString().contains("org.json.simple.JSONArray cannot be cast to     org.json.simple.JSONObject")){                 h=false;             }         }         return h;      } 

文章来源: Test if it is JSONObject or JSONArray