Java Jackson @JsonRawValue

1. Overview

Jackson provides a vast collection of annotations that aid in customizing the serialization and deserialization process of Java objects. Among these annotations is the @JsonRawValue, which is especially useful when you want to include pre-formatted JSON within your serialized output. In this post, we will explore the utility of this annotation using a Student Management System as an example.

@JsonRawValue Annotation Overview

The @JsonRawValue annotation in Jackson is used to instruct the library to serialize a Java property as raw JSON, without further processing. This is especially beneficial when you have a property that already contains a formatted JSON string, and you'd like it to be embedded as-is in the final serialized JSON.

2. Development Steps

1. Create a new Maven project.

2. Add necessary Jackson dependencies.

3. Design a Student class, utilizing the @JsonRawValue annotation.

4. Construct a serialization class.

5. Demonstrate the functionality through a main method.

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

For our Student Management System, consider the following classes:
// Student.java
import com.fasterxml.jackson.annotation.JsonRawValue;
public class Student {
    private int id;
    private String name;
    // Assume this contains a JSON formatted string representing student's grades
    @JsonRawValue
    private String grades;
    public Student(int id, String name, String grades) {
        this.id = id;
        this.name = name;
        this.grades = grades;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public String getGrades() {
        return grades;
    }
}
// StudentSerializer.java
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class StudentSerializer {
    public static String serialize(Student student) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(student);
    }
}
// MainClass.java
public class MainClass {
    public static void main(String[] args) {
        // Embedding raw JSON string for grades
        Student student = new Student(101, "John Doe", "{\"math\": 90, \"english\": 85}");
        try {
            String json = StudentSerializer.serialize(student);
            System.out.println("Serialized JSON: " + json);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
    }
}

Output:

Serialized JSON: {"id":101,"name":"John Doe","grades":{"math": 90, "english": 85}}

Code Explanation:

In our Student class, the property grades is annotated with @JsonRawValue. This instructs Jackson to embed the string value of this property as raw JSON in the serialized output, without quoting or escaping it further. 

The StudentSerializer class takes care of the serialization using Jackson's ObjectMapper. 

The MainClass exhibits the annotation's functionality by creating a Student object and serializing it. The output demonstrates the raw JSON representation of the grades.

6. Conclusion

The @JsonRawValue annotation in Jackson provides an elegant solution to embed pre-existing JSON strings into serialized output, offering flexibility and convenience. This ensures that preformatted JSON content remains untouched, retaining its structure in the serialized result.