Parsing JSON array in Java

Question

I'm currently parsing a JSON file to my Java Program and I ecounter a problem. I get a JSON array that can look like this for example:

[
  {
    "itemType": "magazineArticle",
    "creators": [
      {
        "firstName": "J. Antonio",
        "lastName": "Garcia-Macias",
        "creatorType": "author"
      },
      {
        "firstName": "Jorge",
        "lastName": "Alvarez-Lozano",
        "creatorType": "author"
      },
      {
        "firstName": "Paul",
        "lastName": "Estrada-Martinez",
        "creatorType": "author"
      },
      {
        "firstName": "Edgardo",
        "lastName": "Aviles-Lopez",
        "creatorType": "author"
      }
    ],
    "notes": [],
    "tags": [],
    "title": "Browsing the Internet of Things with Sentient Visors",
    "publicationTitle": "Computer",
    "volume": "44",
    "issue": "5",
    "ISSN": "0018-9162",
    "date": "2011",
    "pages": "46-52",
    "abstractNote": "Unlike the traditional Internet, the emerging Internet of Things constitutes a mix of virtual and physical entities. A proposed IoT browser enables the exploration of augmented spaces by identifying smart objects, discovering any services they might provide, and interacting with them.",
    "extra": "CICESE Research Center, Mexico; CICESE Research Center, Mexico; CICESE Research Center, Mexico; CICESE Research Center, Mexico",
    "libraryCatalog": "IEEE Computer Society"
  }
]

The problem is I have to do a check each time I parse if the field called "extra" is in the array, since it's not included every time i parse. So how do I do that check to see if the field "extra" exists?

Answer 1

Use "has" method of JSONObject like this:

Array.getJSONObject(j).has("extra")

Answer 2

Without framework, you can use JSONObject and JSONArray from org.json.*. Here is an example (not tested). It will allows you to check if the extra key is present

String jsonAsString = "/*Your json as a String*/";
JsonArray jsonArray = new JSONArray(jsonAsString);

for(int i=0; i<jsonArray.length(); i++) {
    JSONObject jsonObject = jsonArray.getJSONObject(i);
    //Get values from your jsonObject
    jsonObject.has("extra"); //Check if extra is present
}