04 Serialization and Deserialization in Java

🧩 Serialization and Deserialization in Java

🔹 Definition

• Serialization → Converting a Java object into a data format (like JSON, XML, or byte stream) for transmission or storage.

• Deserialization → Converting that data format back into a Java object.

These are used widely in API testing (Rest Assured), file storage, network communication, and Java object persistence.

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🔹 Why It’s Important in API Automation

• To send Java objects as JSON/XML in the API request (Serialization).

• To read API responses (JSON/XML) and map them back to Java POJOs for validation (Deserialization).

• Makes tests type-safe, clean, and maintainable.

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🔹 Commonly Used Libraries in Java

✅ Rest Assured uses Jackson by default if it’s on the classpath.

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🔹 Universal Example (Works with Rest Assured or Plain Java)

Step 1: Create a POJO class

public class User {
    private String name;
    private int age;
    private String email;

    // Getters and Setters
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }

    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
}

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Step 2: Serialization (Object → JSON) using Jackson

import com.fasterxml.jackson.databind.ObjectMapper;

User user = new User();
user.setName("Nini");
user.setAge(25);
user.setEmail("nini@test.com");

ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(user);   // ✅ Java → JSON
System.out.println(json);

Output:

{"name":"Nini","age":25,"email":"nini@test.com"}

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Step 3: Deserialization (JSON → Object)

String jsonString = "{\"name\":\"Nini\",\"age\":25,\"email\":\"nini@test.com\"}";

User userObj = mapper.readValue(jsonString, User.class);  // ✅ JSON → Java
System.out.println(userObj.getEmail());

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Step 4: Using in Rest Assured

Serialization (sending Java object as body):

given()
    .contentType("application/json")
    .body(user)    // Rest Assured automatically serializes using Jackson
.when()
    .post("/createUser")
.then()
    .statusCode(201);

Deserialization (converting response to POJO):

User userResponse = 
    given()
        .get("/getUser/101")
    .then()
        .extract()
        .as(User.class);   // Rest Assured uses Jackson to deserialize

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🔹 Advanced Notes for Interviews

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🔹 Common Interview Questions and Universal Answers

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✅ In short (Universal 2-line Interview Answer):

“Serialization is converting a Java object into JSON or XML so it can be sent to an API, and Deserialization is converting JSON or XML back into a Java object. In Rest Assured, this happens automatically using Jackson or Gson libraries, which helps in sending clean requests and validating structured responses.”