How to efficiently merge two JSON Strings based on a common key

Question

I have two JSON strings which are essentially arrays of JSONObject. The two JSON strings have below structure and keys:

JSON-1:

[
    {
        "title": "ABC",
        "edition": 7,
        "year": 2011
    },
    {
        "title": "DEF",
        "edition": 2,
        "year": 2012
    },
    {
        "title": "XYZ",
        "edition": 3,
        "year": 2013
    }
]

And, JSON-2:

[
    {
        "title": "ABC",
        "price": "20"
    },
    {
        "title": "DEF",
        "price": "20"
    },
    {
        "title": "XYZ",
        "price": "20"
    }
]

Both these JSONs have a common key "title" based on which I want to merge these two JSONs, either merging JSON-2 values into JSON-1 or creating a JSON object with the merged result.

The merged result should look like below:

[
    {
        "title": "ABC",
        "edition": 7,
        "year": 2011,
        "price": "20"
    },
    {
        "title": "DEF",
        "edition": 2,
        "year": 2012
        "price": "20"
    },
    {
        "title": "XYZ",
        "edition": 3,
        "year": 2013
        "price": "20"
    }
]

How can I achieve this by minimum looping and minimum object creation? I also can not use entity/model classes. The idea is to do it without creating any model classes.

Note: I cannot use Gson because I don't have the approval to use the same.

I tried to use List<JSONObject> listObj = objectMapper.readValue(jsonOneString, new TypeReference<List<JSONObject>>(){});, but I am getting an unknown property exception.
I tried JsonNode node = objectMapper.readTree(jsonOneString);, but I cannot proceed much further with this approach.

I know what I am doing here is highly inefficient, so looking for ways which will use no entity class, minimum new object creation and minimum loops. Kindly advise.

UPDATE: I updated the below code with a slight modification:

if (json1elem.get("title")!=null 
        && json2elem.get("title")!=null 
            && json1elem.get("title").equals(json2elem.get("title"))) {

    //
}

You "cannot use third-party libraries", yet you're already using a third-party library called Jackson. — Mark Rotteveel, Sep 08 '22 at 17:32
I see what mistake I did there. What I meant by that is, Even though this problem is easily solved with Gson library, currently can't include it in our pom as it needs a lot of approvals. Hence that statement — New2Java, Sep 09 '22 at 01:13

score 0 · Accepted Answer · answered Sep 08 '22 at 17:25

0

JsonNode json1 = objectMapper.readTree(jsonOneString);
JsonNode json2 = objectMapper.readTree(jsonTwoString);
for (JsonNode json1elem : json1) {
    for (JsonNode json2elem : json2) {
        if (json1elem.get("title").equals(json2elem.get("title"))) {
            ((ObjectNode) json1elem).setAll((ObjectNode) json2elem);
            break;
        }
    }
}
System.out.println(json1.toPrettyString());

answered Sep 08 '22 at 17:25

Raymond Choi

1,065
2
7
8

Thanks Raymond. I'll try this out today. Meanwhile could you please help me to understand why is this not working for me: List listObj = objectMapper.readValue(jsonOneString, new TypeReference>(){}); Is there a way to convert jsonOneString into a List ? – New2Java Sep 09 '22 at 02:57
Please check my UPDATE at the bottom of the question. – New2Java Sep 14 '22 at 02:18
You may refer to [this](https://stackoverflow.com/questions/6349421). I haven't verify it. – Raymond Choi Sep 20 '22 at 07:04

How to efficiently merge two JSON Strings based on a common key

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