Ah, right—JSONObject.names() or keySet() only grab the top-level keys, which doesn’t help when you have nested objects or arrays of objects like your data array. The solution here is to use a recursive traversal to dig through every level of the JSON structure and collect all keys along the way.

Here’s a step-by-step implementation using the org.json library (since you’re working with JSONObject):

Step 1: Create a Recursive Helper Method #

This method will take any JSON element (object, array, or primitive) and a set to accumulate keys (using a Set ensures we get unique keys even if they appear in multiple nested objects).

import org.json.JSONArray;
import org.json.JSONObject;
import java.util.HashSet;
import java.util.Set;

private static void collectAllKeys(Object jsonElement, Set<String> keySet) {
    // Handle JSON objects: iterate through keys and recurse on their values
    if (jsonElement instanceof JSONObject) {
        JSONObject jsonObj = (JSONObject) jsonElement;
        for (String key : jsonObj.keySet()) {
            keySet.add(key);
            try {
                Object value = jsonObj.get(key);
                collectAllKeys(value, keySet);
            } catch (Exception e) {
                // Skip any invalid elements (adjust error handling based on your needs)
                e.printStackTrace();
            }
        }
    }
    // Handle JSON arrays: iterate through each element and recurse
    else if (jsonElement instanceof JSONArray) {
        JSONArray jsonArray = (JSONArray) jsonElement;
        for (int i = 0; i < jsonArray.length(); i++) {
            try {
                Object element = jsonArray.get(i);
                collectAllKeys(element, keySet);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    // Primitive values (strings, numbers, booleans, null) have no keys, so do nothing
}

Step 2: Use the Helper Method on Your Root JSONObject #

Call the helper with your root object and a set to collect all keys:

public static void main(String[] args) {
    String yourJson = "{ \"per_page\": 3, \"total\": 12, \"data\": [{ \"color\": \"#98B2D1\", \"year\": 2000, \"name\": \"cerulean\", \"id\": 1, \"pantone_value\": \"15-4020\" }, { \"color\": \"#C74375\", \"year\": 2001, \"name\": \"fuchsia rose\", \"id\": 2, \"pantone_value\": \"17-2031\" } ], \"page\": 1, \"total_pages\": 4 }";
    
    JSONObject rootObj = new JSONObject(yourJson);
    Set<String> allKeys = new HashSet<>();
    
    collectAllKeys(rootObj, allKeys);
    
    // Print all collected keys
    System.out.println("All keys across all levels:");
    allKeys.forEach(System.out::println);
}

What This Does: #

• Starts at the root JSONObject and adds all top-level keys (per_page, total, data, page, total_pages) to the set.
• When it hits the data array, it iterates over each object in the array.
• For each object in the array, it adds its keys (color, year, name, id, pantone_value) to the set.
• Since we’re using a HashSet, duplicate keys (like color appearing in both objects in the data array) are only stored once.

Notes: #

• If you want to keep duplicate keys (though this is unusual for JSON), replace HashSet with ArrayList and add every key you encounter (even duplicates).
• The try-catch blocks handle cases where getting a value might throw a JSONException (e.g., invalid JSON structure). Adjust error handling based on your use case.
• This approach works for any depth of nesting—whether you have objects inside objects inside arrays, etc.

When you run this code, you’ll get exactly the list of keys you need: per_page, total, data, color, year, name, id, pantone_value, page, total_pages.

内容的提问来源于stack exchange，提问作者Sunilkumar 3560