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.
