The previous tutorials have explained the conversion of Java Object to JSON using Gson API. This tutorial explains the process of saving JSON Payload in a file 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 those you do not have source code.
- 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 the below dependency to POM.xml to use Gson API.
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.10.1</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.
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import org.junit.Test;
import java.io.File;
import java.io.FileWriter;
public class WriteJsonFileDemo {
@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\\testData\\EmployeePayloadUsingGson.json");
try {
FileWriter fileWriter = new FileWriter(outputJsonFile);
builder.toJson(employee, fileWriter);
fileWriter.flush();
} catch (Exception e) {
System.out.println(e);
}
}
}
The execution message is shown below.
The JSON file is saved under src/test/resources/testData as shown below image.
We are done! Congratulations on making it through this tutorial and hope you found it useful! Happy Learning!!
QA Automation Expert 