In this article, we will create an example to converting or serializing Java object to JSON representation using the GSON library.
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. In this example, we will show you how you can serialize Java object to JSON using GSON.
GSON Maven Dependency
To use Gson with Maven2/3, you can use the Gson version available in Maven Central by adding the following dependency:
<dependencies>
<!-- Gson: Java to Json conversion -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
<scope>compile</scope>
</dependency>
</dependencies>
Student POJO Class - Object to be Serialized
Let's create a Student class which has one to many relationships with Phone class. Let's create both Student and Phone class and we will seriliaze it to JSON representation using GSON.
class Student {
private long studentId;
private String studentName;
private Set < Phone > studentPhoneNumbers = new HashSet < Phone > (0);
public long getStudentId() {
return studentId;
}
public void setStudentId(long studentId) {
this.studentId = studentId;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public Set < Phone > getStudentPhoneNumbers() {
return studentPhoneNumbers;
}
public void setStudentPhoneNumbers(Set < Phone > studentPhoneNumbers) {
this.studentPhoneNumbers = studentPhoneNumbers;
}
@Override
public String toString() {
return "Student [studentId=" + studentId + ", studentName=" + studentName + ", studentPhoneNumbers=" +
studentPhoneNumbers + "]";
}
}
class Phone {
private long phoneId;
private String phoneType;
private String phoneNumber;
public Phone() {}
public Phone(String phoneType, String phoneNumber) {
this.phoneType = phoneType;
this.phoneNumber = phoneNumber;
}
public long getPhoneId() {
return phoneId;
}
public void setPhoneId(long phoneId) {
this.phoneId = phoneId;
}
public String getPhoneType() {
return phoneType;
}
public void setPhoneType(String phoneType) {
this.phoneType = phoneType;
}
public String getPhoneNumber() {
return phoneNumber;
}
public void setPhoneNumber(String phoneNumber) {
this.phoneNumber = phoneNumber;
}
}
Serialize or Convert Java Object to JSON using GSON
Good to know below points while converting Java Object to JSON using GSON:
- You can not serialize objects with circular references since that will result in infinite recursion.
- Google GSON supports pre-existing objects. This means that we do not need to annotate our classes with any special marker annotations.
- Transient fields are by default ignored when serializing or deserializing.
- While serialization, a null field is skipped from the output.
- While deserialization, a missing entry in JSON results in setting the corresponding field in the object to null.
- Fields corresponding to the outer classes in inner classes, anonymous classes, and local classes are ignored and not included in serialization or deserialization.
package net.javaguides.gson;
import java.util.HashSet;
import java.util.Set;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
/**
*
* @author Ramesh Fadatare
*
*/
public class GSONComplexObjectExample {
public static void main(String[] args) {
serializeStudentObject();
}
private static void serializeStudentObject() {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
Student student = createStudent();
String jsonStr = gson.toJson(student);
System.out.println(jsonStr);
}
private static Student createStudent() {
Student student = new Student();
student.setStudentId(1000);
student.setStudentName("Ramesh");
Set < Phone > phones = new HashSet < Phone > ();
Phone phone = new Phone();
phone.setPhoneId(100);
phone.setPhoneNumber("1234567890");
phone.setPhoneType("Mobile Phone");
phones.add(phone);
Phone phone1 = new Phone();
phone1.setPhoneId(101);
phone1.setPhoneNumber("2222 3333 44");
phone1.setPhoneType("Landline Phone");
phones.add(phone1);
student.setStudentPhoneNumbers(phones);
return student;
}
}
Output:
{
"studentId": 1000,
"studentName": "Ramesh",
"studentPhoneNumbers": [
{
"phoneId": 100,
"phoneType": "Mobile Phone",
"phoneNumber": "1234567890"
},
{
"phoneId": 101,
"phoneType": "Landline Phone",
"phoneNumber": "2222 3333 44"
}
]
}
Complete Example for Reference
package net.javaguides.gson;
import java.util.HashSet;
import java.util.Set;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
/**
*
* @author Ramesh Fadatare
*
*/
public class GSONComplexObjectExample {
public static void main(String[] args) {
serializeStudentObject();
}
private static void serializeStudentObject() {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
Student student = createStudent();
String jsonStr = gson.toJson(student);
System.out.println(jsonStr);
}
private static Student createStudent() {
Student student = new Student();
student.setStudentId(1000);
student.setStudentName("Ramesh");
Set < Phone > phones = new HashSet < Phone > ();
Phone phone = new Phone();
phone.setPhoneId(100);
phone.setPhoneNumber("1234567890");
phone.setPhoneType("Mobile Phone");
phones.add(phone);
Phone phone1 = new Phone();
phone1.setPhoneId(101);
phone1.setPhoneNumber("2222 3333 44");
phone1.setPhoneType("Landline Phone");
phones.add(phone1);
student.setStudentPhoneNumbers(phones);
return student;
}
}
class Student {
private long studentId;
private String studentName;
private Set < Phone > studentPhoneNumbers = new HashSet < Phone > (0);
public long getStudentId() {
return studentId;
}
public void setStudentId(long studentId) {
this.studentId = studentId;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public Set < Phone > getStudentPhoneNumbers() {
return studentPhoneNumbers;
}
public void setStudentPhoneNumbers(Set < Phone > studentPhoneNumbers) {
this.studentPhoneNumbers = studentPhoneNumbers;
}
@Override
public String toString() {
return "Student [studentId=" + studentId + ", studentName=" + studentName + ", studentPhoneNumbers=" +
studentPhoneNumbers + "]";
}
}
class Phone {
private long phoneId;
private String phoneType;
private String phoneNumber;
public Phone() {}
public Phone(String phoneType, String phoneNumber) {
this.phoneType = phoneType;
this.phoneNumber = phoneNumber;
}
public long getPhoneId() {
return phoneId;
}
public void setPhoneId(long phoneId) {
this.phoneId = phoneId;
}
public String getPhoneType() {
return phoneType;
}
public void setPhoneType(String phoneType) {
this.phoneType = phoneType;
}
public String getPhoneNumber() {
return phoneNumber;
}
public void setPhoneNumber(String phoneNumber) {
this.phoneNumber = phoneNumber;
}
}
Output:
{
"studentId": 1000,
"studentName": "Ramesh",
"studentPhoneNumbers": [
{
"phoneId": 100,
"phoneType": "Mobile Phone",
"phoneNumber": "1234567890"
},
{
"phoneId": 101,
"phoneType": "Landline Phone",
"phoneNumber": "2222 3333 44"
}
]
}
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