Converting JSON to Java Map using Jackson

This tutorial demonstrates how to convert a JSON string into a Java Map using Jackson’s ObjectMapper. We will show a basic Java main Class to convert a sample JSON String. Then, we will simplify the classpath set up using JBang.

Prerequisites

• Basic understanding of Java programming.
• Jackson library added to your project’s dependencies.

Steps:

1. Include Jackson Dependency

Make sure to include the Jackson dependencies in your project. If you’re using Maven, add the following to your pom.xml file:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.16.0</version> <!-- Replace with the latest version -->
</dependency>

Create a Java Class

Create a Java class where you’ll perform the conversion from JSON to a Java Map. Let’s name the class JSONToMap.

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.HashMap;
import java.util.Map;

public class JSONToMap {
    public static void main(String[] args) {
        // Sample JSON String
        String jsonString = "{\"name\":\"John Doe\",\"age\":30,\"city\":\"New York\"}";

        // Initialize ObjectMapper
        ObjectMapper objectMapper = new ObjectMapper();

        // Convert JSON to Map
        try {
            // Read JSON string and map it to a Java Map
            Map<String, Object> resultMap = objectMapper.readValue(jsonString, HashMap.class);

            // Print the generated Map
            System.out.println("Generated Map: ");
            for (Map.Entry<String, Object> entry : resultMap.entrySet()) {
                System.out.println(entry.getKey() + " : " + entry.getValue());
            }
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

3. Run the Code

Replace the jsonString variable with your actual JSON content. Execute the code, and it will convert the JSON string into a Java Map using Jackson’s ObjectMapper.

Run the example with JBang

Finally, if you want to run the above example as a Java script command, we recommend using JBang. For more info about JBang check this article: JBang: Create Java scripts like a pro

By using JBang, you can skip the project creation and just include the dependency on top of the Java Class:

//usr/bin/env jbang "$0" "$@" ; exit $?
//DEPS com.fasterxml.jackson.core:jackson-databind:2.16.0

Then, run it as follows:

Conclusion

In this tutorial, you’ve learned how to utilize Jackson’s ObjectMapper to convert a JSON string into a Java Map. This capability is beneficial for parsing JSON data into a format that’s easily manipulable within Java applications.