Java Jackson @JsonPropertyOrder

1. Overview

Jackson provides a suite of annotations that help in customizing the serialization of Java objects to JSON format. One such annotation is @JsonPropertyOrder, which governs the order in which properties appear in the serialized JSON. This blog post delves into how this annotation can be used, taking a Student Management System as a reference.

@JsonPropertyOrder Annotation Overview

The @JsonPropertyOrder annotation in Jackson allows users to specify the order in which properties are serialized to JSON. The properties to be serialized are mentioned in the annotation in the desired order. If a property is omitted, it will be serialized after the ordered ones.

2. Development Steps

1. Set up a new Maven project.

2. Add Jackson dependencies.

3. Create a Student class and annotate it with @JsonPropertyOrder.

4. Write a class to handle serialization.

5. Design a main method to showcase the functionality.

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 the Student Management System:
// Student.java
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
@JsonPropertyOrder({ "id", "name", "age" })
public class Student {
    private int id;
    private String name;
    private int age;
    public Student(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
    public int getId() {
        return id;
    }
    public String getName() {
        return name;
    }
    public int getAge() {
        return age;
    }
}
// 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) {
        Student student = new Student(101, "John Doe", 20);
        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","age":20}

Code Explanation:

In the Student class, the @JsonPropertyOrder annotation specifies the order in which properties should be serialized. Thus, the "id" property gets serialized first, followed by "name" and then "age". 

The StudentSerializer class handles the serialization using the Jackson library. 

The MainClass is where the demonstration takes place. Here, we create a Student object and serialize it, observing the custom property order in the output.

6. Conclusion

Jackson's @JsonPropertyOrder annotation furnishes a simple and effective mechanism to control the order of properties in the serialized JSON output. It provides the flexibility to shape the output according to specific requirements, making it a valuable tool in the Java serialization toolkit.