Java Jackson @JsonSerialize

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1. Overview

Jackson offers a powerful suite of annotations to customize the way Java objects are serialized into JSON and vice versa. One of the most versatile annotations is @JsonSerialize, which is employed to specify a custom serializer for an object. In this tutorial, we'll delve into the utilization of this annotation using an Employee Management System as our example.

@JsonSerialize Annotation Overview

The @JsonSerialize annotation in Jackson is employed to define a custom serializer for a Java object or property. It grants developers increased control over the JSON output, allowing for more tailored serialization than what's provided out-of-the-box by Jackson.

2. Development Steps

1. Establish a new Maven project.

2. Add the requisite Jackson dependencies.

3. Construct an Employee class, employing the @JsonSerialize annotation.

4. Define a custom serializer class.

5. Create a demonstration class with the 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 Employee Management System, consider the subsequent classes: // Employee.java import com.fasterxml.jackson.databind.annotation.JsonSerialize; public class Employee { private int empId; private String empName; private double salary; @JsonSerialize(using = SalarySerializer.class) public double getSalary() { return salary; } public Employee(int empId, String empName, double salary) { this.empId = empId; this.empName = empName; this.salary = salary; } public int getEmpId() { return empId; } public String getEmpName() { return empName; } } // SalarySerializer.java import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializerProvider; import java.io.IOException; public class SalarySerializer extends JsonSerializer<Double> { @Override public void serialize(Double value, JsonGenerator gen, SerializerProvider serializers) throws IOException { // Display salary rounded to two decimal places gen.writeString(String.format("%.2f", value)); } } // MainClass.java import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.ObjectMapper; public class MainClass { public static void main(String[] args) { Employee employee = new Employee(1, "Alice", 5000.4567); ObjectMapper mapper = new ObjectMapper(); try { String json = mapper.writeValueAsString(employee); System.out.println("Serialized JSON: " + json); } catch (JsonProcessingException e) { e.printStackTrace(); } } } 

Output:

Serialized JSON: {"empId":1,"empName":"Alice","salary":"5000.46"} 

Code Explanation:

In the Employee class, the salary property uses the @JsonSerialize annotation to specify SalarySerializer as its serializer. This custom serializer, SalarySerializer, modifies the serialization of the salary property to round to two decimal places. The MainClass shows