Introduction:

JSON (JavaScript Object Notation) is a popular data interchange format that is extensively used in modern software development. In Java, converting a JSON array to a Map can be a common requirement, as it allows for easy data manipulation and retrieval. In this blog, we will explore various methods to convert a JSON array into a Map in Java.

Method 1: Using Jackson Library

Jackson is a powerful and widely used Java library for JSON processing. It provides a straightforward approach to convert JSON data to Java objects and vice versa. Let's see how we can use Jackson to convert a JSON array into a Map.

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JsonToMapConversion {

    public static void main(String[] args) {
        String jsonString = "[{\"key1\":\"value1\"},{\"key2\":\"value2\"}]";
        ObjectMapper objectMapper = new ObjectMapper();
        
        try {
            // Convert JSON array to List of Maps
            List<Map<String, Object>> list = objectMapper.readValue(jsonString, new TypeReference<>() {});
            
            // Merge individual Maps into a single Map
            Map<String, Object> map = new HashMap<>();
            list.forEach(map::putAll);
            
            // Output the result
            System.out.println("Method 1: Using Jackson Library");
            System.out.println("Converted Map: " + map);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Output:

Method 1: Using Jackson Library
Converted Map: {key1=value1, key2=value2}

In this method, we start by importing the necessary classes from the Jackson library. We then create a JSON array as a string representation. Using the ObjectMapper class from Jackson, we convert the JSON array into a List of Maps. Finally, we merge all individual Maps from the List into a single Map using the putAll() method. The resulting Map contains all the key-value pairs from the JSON array.

Method 2: Using Gson Library

Gson is another widely used Java library for working with JSON data. It simplifies the process of converting JSON data to Java objects and vice versa. Now, let's see how we can use Gson to achieve the same JSON array to Map conversion.

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class JsonToMapConversion {

    public static void main(String[] args) {
        String jsonString = "[{\"key1\":\"value1\"},{\"key2\":\"value2\"}]";
        Gson gson = new Gson();
        
        // Convert JSON array to List of Maps
        List<Map<String, Object>> list = gson.fromJson(jsonString, new TypeToken<List<Map<String, Object>>>() {}.getType());
        
        // Merge individual Maps into a single Map
        Map<String, Object> map = new HashMap<>();
        list.forEach(map::putAll);
        
        // Output the result
        System.out.println("Method 2: Using Gson Library");
        System.out.println("Converted Map: " + map);
    }
}

Output:

Method 2: Using Gson Library
Converted Map: {key1=value1, key2=value2}

In this method, we import the required classes from the Gson library and create the same JSON array as in the previous example. Using the Gson object, we convert the JSON array into a List of Maps. Then, similar to Method 1, we merge the individual Maps from the List into a single Map. The output will again contain all the key-value pairs from the JSON array.

Conclusion:

In this blog, we explored two popular methods to convert a JSON array into a Map in Java. We leveraged the power of Jackson and Gson libraries, both of which are excellent choices for JSON manipulation in Java.