Java Jackson @JsonIgnore

1. Overview

Jackson is a widely-used library for Java that allows for easy serialization and deserialization of Java objects to and from JSON. One of the annotations provided by the Jackson Library is @JsonIgnore. This annotation is used to ignore certain properties during serialization and deserialization processes. This is especially useful when you want to hide or omit sensitive or unnecessary data when converting between JSON and Java objects.

Jackson @JsonIgnore Annotation Overview

The @JsonIgnore annotation is placed above a field or getter method of a Java object to indicate that this particular property should not be considered during serialization or deserialization. This ensures that the specified field is neither included in the generated JSON output nor populated from an incoming JSON during deserialization.

2. Development Steps

1. Kickstart a new Maven project.

2. Integrate the essential Jackson dependencies.

3. Design the Employee class and apply the @JsonIgnore annotation to specific fields.

4. Develop a separate class responsible for the serialization process.

5. Establish a primary class to illustrate the serialization.

3. Create a Maven Project

There are different ways to create a simple Maven project:

Create a Simple Maven Project using the Command Line Interface

Create a Simple Maven Project using  Eclipse IDE

Create a Simple Maven Project using  IntelliJ IDEA

4. Maven Dependencies

Open the pom.xml file, and add the following Jackson data binding dependency:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.13.0</version>
</dependency>

5. Code Program

// Employee.java
import com.fasterxml.jackson.annotation.JsonIgnore;
public class Employee {
    private String name;
    private int age;
    // Ignoring this field during serialization
    @JsonIgnore
    private String ssn;
    // Standard constructors, getters, and setters...
}

// JsonSerializer.java
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JsonSerializer {
    public static String serializeToJson(Object object) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(object);
    }
}

// MainClass.java
public class MainClass {
    public static void main(String[] args) {
        Employee emp = new Employee();
        emp.setName("Jane Smith");
        emp.setAge(30);
        emp.setSsn("123-45-6789");
        try {
            String json = JsonSerializer.serializeToJson(emp);
            System.out.println(json);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

Output:

{"name":"Jane Smith","age":30}

Code Explanation:

In the Employee class, we have an ssn (Social Security Number) field annotated with @JsonIgnore. This indicates to Jackson that when the Employee object is serialized, the ssn field should be omitted.

The JsonSerializer class is a utility class responsible for the serialization, using Jackson's ObjectMapper. 

The MainClass brings everything together: it creates an Employee instance, triggers the serialization through JsonSerializer, and then prints the resulting JSON.

6. Conclusion

The @JsonIgnore annotation in Jackson provides a straightforward approach for developers to exercise control over what gets included in the JSON output. This offers a balance between data transparency and privacy, making sure only the necessary data is exposed.