Create JSON object using Jackson in Java

Question

I need to create a JSON string as below using Jackson. I know similar question has been answered already here: Creating a json object using jackson

But my expected JSON string is a little different from the one in above example.

How can I form the below formatted JSON object in Java using only Jackson? Also, I do not prefer creating a separate POJO to achieve this.

Expected Output:

{
    "obj1": {
        "name1": "val1",
        "name2": "val2"
    },
    "obj2": {
        "name3": "val3",
        "name4": "val4"
    },
    "obj3": {
        "name5": "val5",
        "name6": "val6"
    }
}

@Yogesh_D If you see the output format of my question and the one you mentioned, they are a little different. I need the output to be exactly in the above mentioned format in my question. — Shashank Shekher, Dec 05 '16 at 06:04
@Jerry06 Input does not matter, I just need to fetch some details from DB or elsewhere and form this JSON String. — Shashank Shekher, Dec 05 '16 at 06:55
This question is not a duplicate. Shouldn't have been marked as duplicate. — Sorter, Jun 22 '20 at 15:58
It is quite bad idea to not create POJO for such task in Java. If I would see such attempt during code review I would ultimately reject it and return it back to creator to fix it. — Jurass, Nov 21 '20 at 10:46
@Jurass Creating a POJO here will not make any sense as the input is not a fixed type. It can differ in many ways. Hope you have read the question clearly. — Shashank Shekher, Nov 23 '20 at 03:33

score 123 · Accepted Answer · edited Oct 12 '20 at 12:36

123

Try this:

ObjectMapper mapper = new ObjectMapper();
ObjectNode rootNode = mapper.createObjectNode();

ObjectNode childNode1 = mapper.createObjectNode();
childNode1.put("name1", "val1");
childNode1.put("name2", "val2");

rootNode.set("obj1", childNode1);

ObjectNode childNode2 = mapper.createObjectNode();
childNode2.put("name3", "val3");
childNode2.put("name4", "val4");

rootNode.set("obj2", childNode2);

ObjectNode childNode3 = mapper.createObjectNode();
childNode3.put("name5", "val5");
childNode3.put("name6", "val6");
    
rootNode.set("obj3", childNode3);


String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(rootNode);
System.out.println(jsonString);

edited Oct 12 '20 at 12:36

Jimothy

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answered Dec 05 '16 at 06:46

Sachin Gupta

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I tried this but I keep getting ObjectNode cannot be resolved to a type – Zeusox Apr 09 '19 at 18:01
this adds backslash to the added strings. How to avoid the backslash? – Deepak Selvakumar Jul 02 '19 at 18:12
@DeepakSelvakumar if you want to avoid that backslash, replace `writerWithDefaultPrettyPrinter()` in the second last line with `writer()`. You're good to go! – Prasannjeet Singh Sep 22 '21 at 19:37

Create JSON object using Jackson in Java

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