java - Convert JSON object with duplicate keys to JSON array

Question

I have a JSON string that I get from a database which contains repeated keys. I want to remove the repeated keys by combining their values into an array.

For example

Input

{
"a":"b",
"c":"d",
"c":"e",
"f":"g"
}

Output

{
"a":"b",
"c":["d","e"],
"f":"g"
}

The actual data is a large file that may be nested. I will not know ahead of time what or how many pairs there are.

I need to use Java for this. org.json throws an exception because of the repeated keys, gson can parse the string but each repeated key overwrites the last one. I need to keep all the data.

If possible, I'd like to do this without editing any library code

Answer 1

As of today the org.json library version 20170516 provides accumulate() method that stores the duplicate key entries into JSONArray

JSONObject jsonObject = new JSONObject();
jsonObject.accumulate("a", "b");
jsonObject.accumulate("c", "d");
jsonObject.accumulate("c", "e");
jsonObject.accumulate("f", "g");
System.out.println(jsonObject);

Output:

{  
    "a":"b",  
    "c":["d","e"],  
    "f":"g"  
}