Handling various JSON responses in Java without relying on Plain Old Java Objects (POJO) classes

I am working with JSON responses from a REST API in Java, but I am looking for a solution that doesn't require creating a Java class (POJO) for each response due to the varying data structures and fields. Is there a more versatile JSON parser in Java that offers a syntax similar to JavaScript's simplicity?

The following JSON represents one example of the many responses from different REST endpoints

{
    "f1" : "volume",
    "f2" : "gender",
    "f3" : "days",
    "f4" : [{
            "id" : "F",
            "name" : "female",
            "values" : [{
                    "name" : "September",
                    "value" : 12
                }
            ]
        }, {
            "id" : "M",
            "name" : "male",
            "values" : [{
                    "name" : "September",
                    "value" : 11
                }
            ]
        }
    ]
}

In JavaScript, you can access the value for female like this:

jsonRoot.f4[0].values[0].value

This approach is cleaner than creating numerous Java classes. Do you have any suggestions for a similar solution or a way to avoid generating multiple POJOs?

javascriptjavajson

Answer №1

When utilizing the com.google.gson jar, extracting a value can be achieved in the following manner:

     String str="{" +
            "    \"f1\" : \"volume\"," +
            "    \"f2\" : \"gender\"," +
            "    \"f3\" : \"days\"," +
            "    \"f4\" : [{" +
            "            \"id\" : \"F\"," +
            "            \"name\" : \"female\"," +
            "            \"values\" : [{" +
            "                    \"name\" : \"September\"," +
            "                    \"value\" : 12" +
            "                }" +
            "            ]" +
            "        }, {" +
            "            \"id\" : \"M\"," +
            "            \"name\" : \"male\"," +
            "            \"values\" : [{" +
            "                    \"name\" : \"September\"," +
            "                    \"value\" : 11" +
            "                }" +
            "            ]" +
            "        }" +
            "    ]" +
            "}";
    JsonParser parser=new JsonParser();
    JsonObject object=(JsonObject)parser.parse(str);
    String value=object.get("f4").getAsJsonArray().get(0).getAsJsonObject()
            .get("values").getAsJsonArray().get(0).getAsJsonObject()
            .get("value").getAsString();

Answer №2

Using Jackson to map to a Map<String, Object> is an acceptable approach:

    String jsonData = "{\"f4\":[1, 2]}"

    try {
        Map<String, Object> mappedValue = mapper.readValue(jsonData, Map.class);
        System.out.println(mappedValue.get("f4"));
    } catch (IOException ex) {
        ex.printStackTrace();
    }

Creating a POJO object for this purpose provides static type checking, and I advise doing so.

Answer №3

    String s="[0,{\"1\":{\"2\":{\"3\":{\"4\":[5,{\"6\":7}]}}}}]";
    Object obj=JSONValue.parse(s);
    JSONArray array=(JSONArray)obj;
    System.out.println(array.get(1));       
    System.out.println(((JSONObject)array.get(1)).get("1"));

explore more examples here

download json-simple.jar

Answer №4

The org.json library can be utilized for this purpose.

If you are using Maven:

    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20150729</version>
    </dependency>

Alternatively, you can download the JAR file from: http://mvnrepository.com/artifact/org.json/json

Here is a Java example:

import org.json.JSONObject;

public class JSONExample {

    public static void main(String[] args) {

        JSONObject jsonObject = new JSONObject("{'f1' : 'volume', 'f2' : 'gender', 'f3' : 'days'}"); // Truncated for demonstration purposes

        String f1Value = jsonObject.getString("f1");
        System.out.println(f1Value);
    }
}

You can also access arrays:

JSONArray f4Array = jsonObject.getJSONArray("f4");

Then iterate over the array elements:

for (int i = 0; i < f4Array.length(); i++){
        String id = f4Array.getJSONObject(i).getString("id");
        String name = f4Array.getJSONObject(i).getString("name");
        System.out.println(name);
        System.out.println(id);
        JSONArray values = f4Array.getJSONObject(i).getJSONArray("values");
        for (int j = 0; j < values.length(); j++){
            String valueName = values.getJSONObject(j).getString("name");
            int numValue = values.getJSONObject(j).getInt("value");
            System.out.println(valueName);
            System.out.println(numValue);
        }

    }

Answer №5

If you're utilizing jQuery, remember that there's a parseJson() function available for data parsing.

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