How to test JSON Request using GSON API

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In this tutorial, I will explain the testing of a JSON Payload using GSON API.

Refer to the below tutorials to understand how GSON works:-

Serialization – How to convert Java Object To JSON Object Using Gson API

Deserialization – How to create JSON Object to JAVA Object Using Gson API

Add below dependency to POM.xml to use Gson API.

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.9</version>
</dependency>

As we know, we can use toJson() to convert the JAVA objects to JSON Payload.

In the below example, I have created a POJO class with the name of EmployeeDetails. This class contains the data members corresponding to the JSON nodes and their corresponding getter and setter methods.

public class EmployeeDetails {

	// private variables or data members of pojo class
	private String name;
	private double salary;
	private int age;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public int getAge() {
		return age;
	}

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

}

Below, will create a JSON payload and pass it as a request body to the Rest API.

	@Test
	public void createEmployee() throws IOException {

		// Just create an object of Pojo class
		EmployeeDetails emp = new EmployeeDetails();
		emp.setName("GsonTest");
		emp.setSalary(50000);
		emp.setAge(25);

		// Converting a Java class object to a JSON payload as string using Gson
		Gson builder = new GsonBuilder().setPrettyPrinting().create();
		String employeePrettyJsonPayload = builder.toJson(emp);
		System.out.println("Request");
		System.out.println(employeePrettyJsonPayload);
		System.out.println("=========================================");
		System.out.println("Response");

		// GIVEN
		given()
              .baseUri("http://dummy.restapiexample.com/api")
              .contentType(ContentType.JSON).body(emp)

		// WHEN
		.when()
               .post("/v1/create")

		// THEN
		.then()
              .assertThat().statusCode(200)
              .body("status", equalTo("success"))
			  .body("data.name", equalTo("GsonTest"))
              .body("data.salary", equalTo(50000))
			  .body("data.age", equalTo(25))
              .body("message", equalTo("Successfully! Record has been added."))
              .log().body();

	}
}

Output

We are done! Congratulations on making it through this tutorial and hope you found it useful! Happy Learning!!

Deserialization – How to create JSON Object to JAVA Object Using Gson API

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In this tutorial, I will explain the conversion of JSON Object (payload) to JAVA Object. We will use Gson API for the same purpose.

Before going through this tutorial, spend some time understanding Serialization using Gson API.

We can parse the JSON or XML response into POJO classes. After parsing into POJO classes, we can easily get values from the response easily. This is called De-serialization. For this, we can use any JSON parser APIs. Here, we are going to use Gson API.

To start with, add the below dependency to the project.

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.9</version>
</dependency>

Sample JSON Payload

{
  "firstName" : "Vibha",
  "lastName" : "Singh",
  "age" : 30,
  "salary" : 75000.0,
  "designation" : "Manager",
  "contactNumber" : "+91999996712",
  "emailId" : "abc123@test.com"
}

Let us create a class called Employee with field name exactly (case-sensitive) the same as node names in above JSON string because with default setting while parsing JSON object to Java object, it will look on getter setter methods of field names. 

public class Employee {

	// private variables or data members of POJO class
	private String firstName;
	private String lastName;
	private int age;
	private double salary;
	private String designation;
	private String contactNumber;
	private String emailId;

	// Getter and setter methods
	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	public int getAge() {
		return age;
	}

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

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public String getDesignation() {
		return designation;
	}

	public void setDesignation(String designation) {
		this.designation = designation;
	}

	public String getContactNumber() {
		return contactNumber;
	}

	public void setContactNumber(String contactNumber) {
		this.contactNumber = contactNumber;
	}

	public String getEmailId() {
		return emailId;
	}

	public void setEmailId(String emailId) {
		this.emailId = emailId;
	}

}

Gson class provides multiple overloaded fromJson() methods to achieve this. Below is a list of available methods:-

In the below test, I have mentioned the JSON Payload string in the test and used Gson API to deserialize the JSON payload to JAVA Object.

   @Test
	public void getDetailFromJson() {
		
		// De-serializing from JSON String
		String jsonString = "{\r\n" + "  \"firstName\": \"Tom\",\r\n" + "  \"lastName\": \"John\",\r\n"
				+ "  \"age\": 30,\r\n" + "  \"salary\": 50000.0,\r\n" + "  \"designation\": \"Lead\",\r\n"
				+ "  \"contactNumber\": \"+917642218922\",\r\n" + "  \"emailId\": \"abc@test.com\"\r\n" + "}";

		Gson gson = new Gson();
		// Pass JSON string and the POJO class
		Employee employee = gson.fromJson(jsonString, Employee.class);

		// Now use getter method to retrieve values
		System.out.println("Details of Employee is as below:-");
		System.out.println("First Name : " + employee.getFirstName());
		System.out.println("Last Name : " + employee.getLastName());
		System.out.println("Age : " + employee.getAge());
		System.out.println("Salary : " + employee.getSalary());
		System.out.println("designation : " + employee.getDesignation());
		System.out.println("contactNumber : " + employee.getContactNumber());
		System.out.println("emailId : " + employee.getEmailId());
		System.out.println("########################################################");

	}

Output

We can get the JSON payload from a file present in a project under src/test/resources as shown in the below image.

public class EmployeeDeserializationGsonTest {

	@Test
	public void fromFile() throws FileNotFoundException {

		Gson gson = new Gson();
		// De-serializing from a json file
		String userDir = System.getProperty("user.dir");
		File inputJsonFile = new File(userDir + "\\src\\test\\resources\\EmployeePayloadUsingGson.json");
		FileReader fileReader = new FileReader(inputJsonFile);
		Employee employee1 = gson.fromJson(fileReader, Employee.class);

		// Now use getter method to retrieve values
		System.out.println("Details of Employee is as below:-");
		System.out.println("First Name : " + employee1.getFirstName());
		System.out.println("Last Name : " + employee1.getLastName());
		System.out.println("Age : " + employee1.getAge());
		System.out.println("Salary : " + employee1.getSalary());
		System.out.println("designation : " + employee1.getDesignation());
		System.out.println("contactNumber : " + employee1.getContactNumber());
		System.out.println("emailId : " + employee1.getEmailId());
		System.out.println("########################################################");
	}
}

Output

We are done! Congratulations on making it through this tutorial and hope you found it useful! Happy Learning!!

Serialization¬†– How to convert Java Object To JSON Object Using Gson API

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The previous tutorials have explained the conversion of Java Object to JSON and JSON payload to Java Objects using Jackson API. This tutorial explains the process to convert Java Object to JSON Payload using Gson API.

Gson is a Java library that can be used to convert Java Objects into their JSON representation. It can also be used to convert a JSON string to an equivalent Java object. Gson can work with arbitrary Java objects, including pre-existing objects that you do not have source code of.

  • Provide simple toJson()¬†and fromJson()¬†methods to convert Java objects to JSON and vice-versa.
  • Allow pre-existing unmodifiable objects to be converted to and from JSON.
  • Extensive support of Java Generics.
  • Allow custom representations for objects.
  • Support arbitrarily complex objects (with deep inheritance hierarchies and extensive use of generic types).

Add below dependency to POM.xml to use Gson API.

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.9</version>
</dependency>

Let us take an example of a JSON.

{
  "firstName" : "Vibha",
  "lastName" : "Singh",
  "age" : 30,
  "salary" : 75000.0,
  "designation" : "Manager",
  "contactNumber" : "+919999988822",
  "emailId" : "abc@test.com"
  }

Let us create a table named Employee which contains the data members same as node names in the above JSON payload and their corresponding getter and setter methods.

public class Employee {

	// private data members of POJO class
	private String firstName;
	private String lastName;
	private int age;
	private double salary;
	private String designation;
	private String contactNumber;
	private String emailId;

	// Getter and setter methods
	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	public int getAge() {
		return age;
	}

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

	public double getSalary() {
		return salary;
	}

	public void setSalary(double salary) {
		this.salary = salary;
	}

	public String getDesignation() {
		return designation;
	}

	public void setDesignation(String designation) {
		this.designation = designation;
	}

	public String getContactNumber() {
		return contactNumber;
	}

	public void setContactNumber(String contactNumber) {
		this.contactNumber = contactNumber;
	}

	public String getEmailId() {
		return emailId;
	}

	public void setEmailId(String emailId) {
		this.emailId = emailId;
	}

}

We will convert a Java Object to a JSON object as a String and also will write it into a .json file. There are many variations for the method toJson().

You can create a Gson instance by invoking a new Gson() if the default configuration is all you need, as shown in the below example.

You can also use GsonBuilder to build a Gson instance with various configuration options such as versioning support, pretty-printing, custom JsonSerializer, JsonDeserializer.

public class EmployeeGsonTest {

	@Test
	public void gsonSerializationTest()  {

		// Create an object of POJO class
		Employee employee = new Employee();
		employee.setFirstName("Vibha");
		employee.setLastName("Singh");
		employee.setAge(30);
		employee.setSalary(75000);
		employee.setDesignation("Manager");
		employee.setContactNumber("+919999988822");
		employee.setEmailId("abc@test.com");

		Gson gson = new Gson();
		String employeeJsonPayload = gson.toJson(employee);
		System.out.println(employeeJsonPayload);

		Gson builder = new GsonBuilder().setPrettyPrinting().create();
		String employeePrettyJsonPayload = builder.toJson(employee);
		System.out.println(employeePrettyJsonPayload);

	}
}

The execution message is shown below.

We can save this JSON payload as a file under our project or any location. Here, in the below example, will save the JSON payload under src/test/resources.

   @Test
	public void saveJsonToFile() {

	    Employee employee = new Employee();
		employee.setFirstName("Vibha");
		employee.setLastName("Singh");
		employee.setAge(30);
		employee.setSalary(75000);
		employee.setDesignation("Manager");
		employee.setContactNumber("+919999988822");
		employee.setEmailId("abc@test.com");

		Gson builder = new GsonBuilder().setPrettyPrinting().create();
		String employeePrettyJsonPayload = builder.toJson(employee);
		System.out.println(employeePrettyJsonPayload);

		String userDir = System.getProperty("user.dir");
		File outputJsonFile = new File(userDir + "\\src\\test\\resources\\EmployeePayloadUsingGson.json");
		try {
			FileWriter fileWriter = new FileWriter(outputJsonFile);
			builder.toJson(employee, fileWriter);
			fileWriter.flush();
		} catch (Exception e) {
			System.out.println(e);
		}
	}

The JSON file is saved under src/test/resources as shown below image.

We are done! Congratulations on making it through this tutorial and hope you found it useful! Happy Learning!!