How do I access members of items in a JSONArray in Java?

General Discussions
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1

I’m new to working with JSON in Java and unsure how to extract string values from a JSONArray Java object. My JSON structure looks like this:

{
  "locations": {
    "record": [
      {
        "id": 8817,
        "loc": "NEW YORK CITY"
      },
      {
        "id": 2873,
        "loc": "UNITED STATES"
      },
      {
        "id": 1501,
        "loc": "NEW YORK STATE"
      }
    ]
  }
}

I can retrieve the "record" JSONArray using:

JSONObject req = new JSONObject(join(loadStrings(data.json), ""));
JSONObject locs = req.getJSONObject("locations");
JSONArray recs = locs.getJSONArray("record");

But I’m unsure how to loop through it and access the "id" and "loc" values. What’s the correct way to do this?

2

You’re on the right track! Once you have the JSONArray, you can loop through it using getJSONObject(index).

Here’s how you can access “id” and “loc” values:

for (int i = 0; i < recs.length(); i++) {
    JSONObject obj = recs.getJSONObject(i);
    int id = obj.getInt("id");
    String loc = obj.getString("loc");
    System.out.println("ID: " + id + ", Location: " + loc);
}
  • :heavy_check_mark: Simple and readable
  • :x: Throws exceptions if keys are missing
3

Good approach! But what if “id” or “loc” are missing or have unexpected types?

We should handle that:

for (int i = 0; i < recs.length(); i++) {
    JSONObject obj = recs.optJSONObject(i);
    if (obj != null) {
        int id = obj.optInt("id", -1); // Default -1 if missing
        String loc = obj.optString("loc", "Unknown"); // Default "Unknown" if missing
        System.out.println("ID: " + id + ", Location: " + loc);
    }
}
  • Avoids exceptions for missing keys
  • Provides default values
4

Both solutions work well, but if you prefer a more modern, functional approach, try Java Streams:

IntStream.range(0, recs.length())
    .mapToObj(recs::getJSONObject)
    .forEach(obj -> {
        int id = obj.optInt("id", -1);
        String loc = obj.optString("loc", "Unknown");
        System.out.println("ID: " + id + ", Location: " + loc);
    });
  • Concise & elegant (especially for large JSON data)
  • Avoids index-based looping