Convert object to/from json using Gson

Posted on August 16, 2016 Updated on August 19, 2016

Google GSON is JSON parser and also generator for java, which is widely use to convert object to/from Json. To learn more about Gson one can refer to Gson tutorial. GSON library is used to convert any object to Json and vice-versa. Here in this tutorial we’ll be discussing below popular examples to convert different object to/from Json.

Convert Object to/from Json.
Convert List of objects to/from Json.
Convert Map containing objects.

Simple POJO which will be used as an object in all examples.

public class Emp {
	private int id;
	private String firstName;
	private String lastName;
 
	public Emp() {}
 
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	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;
	}
 
	@Override
	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append("Id : " + id);
		sb.append(", FirstName : " + firstName);
		sb.append(", LastName : " + lastName);
 
		return sb.toString();
	}
}

public class Emp {

private int id;

private String firstName;

private String lastName;

public Emp() {}

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

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;

}

@Override

public String toString() {

StringBuilder sb = new StringBuilder();

sb.append("Id : " + id);

sb.append(", FirstName : " + firstName);

sb.append(", LastName : " + lastName);

return sb.toString();

}

1) Convert Object to/from Json

Example to convert Emp object to Json.

Emp emp = new Emp();
emp.setId(1);
emp.setFirstName("Rahul");
emp.setLastName("Anand");
		
Gson gson = new Gson();
String jsonString = gson.toJson(emp);
System.out.println(jsonString);

Emp emp = new Emp();

emp.setId(1);

emp.setFirstName("Rahul");

emp.setLastName("Anand");

Gson gson = new Gson();

String jsonString = gson.toJson(emp);

System.out.println(jsonString);

Output

{"id":1,"firstName":"Rahul","lastName":"Anand"}

1	{"id":1,"firstName":"Rahul","lastName":"Anand"}

Example to convert Json to Emp object.

String jsonString = "{\"id\":1,\"firstName\":\"Rahul\",\"lastName\":\"Anand\"}";
Gson gson = new Gson();
Emp emp = gson.fromJson(jsonString, Emp.class);
System.out.println(emp);

String jsonString = "{\"id\":1,\"firstName\":\"Rahul\",\"lastName\":\"Anand\"}";

Gson gson = new Gson();

Emp emp = gson.fromJson(jsonString, Emp.class);

System.out.println(emp);

Output

Id : 1, FirstName : Rahul, LastName : Anand

1	Id : 1, FirstName : Rahul, LastName : Anand

2) Convert List of objects to/from Json

Example to convert List of Emp objects to Json.

List<Emp> employees = new ArrayList<Emp>(); 
Emp emp1 = new Emp();
emp1.setId(1);
emp1.setFirstName("Rahul");
emp1.setLastName("Anand");
		
Emp emp2 = new Emp();
emp2.setId(2);
emp2.setFirstName("Daniel");
emp2.setLastName("Anderson");
		
employees.add(emp1);
employees.add(emp2);
		
Gson gson = new Gson();
String jsonString = gson.toJson(employees);
System.out.println(jsonString);

List<Emp> employees = new ArrayList<Emp>();

Emp emp1 = new Emp();

emp1.setId(1);

emp1.setFirstName("Rahul");

emp1.setLastName("Anand");

Emp emp2 = new Emp();

emp2.setId(2);

emp2.setFirstName("Daniel");

emp2.setLastName("Anderson");

employees.add(emp1);

employees.add(emp2);

Gson gson = new Gson();

String jsonString = gson.toJson(employees);

System.out.println(jsonString);

Output

[{"id":1,"firstName":"Rahul","lastName":"Anand"},{"id":2,"firstName":"Daniel","lastName":"Anderson"}]

1	[{"id":1,"firstName":"Rahul","lastName":"Anand"},{"id":2,"firstName":"Daniel","lastName":"Anderson"}]

Example to convert Json to List of Emp objects.

String jsonString = "[{\"id\":1,\"firstName\":\"Rahul\",\"lastName\":\"Anand\"},{\"id\":2,\"firstName\":\"Daniel\",\"lastName\":\"Anderson\"}]";
Gson gson = new Gson();
List<Emp> employees = gson.fromJson(jsonString, new TypeToken<List<Emp>>(){}.getType());
System.out.println(employees);

String jsonString = "[{\"id\":1,\"firstName\":\"Rahul\",\"lastName\":\"Anand\"},{\"id\":2,\"firstName\":\"Daniel\",\"lastName\":\"Anderson\"}]";

Gson gson = new Gson();

List<Emp> employees = gson.fromJson(jsonString, new TypeToken<List<Emp>>(){}.getType());

System.out.println(employees);

Json object in user readable format.

[
  {
    "id": 1,
    "firstName": "Rahul",
    "lastName": "Anand"
  },
  {
    "id": 2,
    "firstName": "Daniel",
    "lastName": "Anderson"
  }
]

[

{

"id": 1,

"firstName": "Rahul",

"lastName": "Anand"

{

"id": 2,

"firstName": "Daniel",

"lastName": "Anderson"

}

]

Output

[Id : 1, FirstName : Rahul, LastName : Anand, Id : 2, FirstName : Daniel, LastName : Anderson]

1	[Id : 1, FirstName : Rahul, LastName : Anand, Id : 2, FirstName : Daniel, LastName : Anderson]

3) Convert Map containing objects.

Example to convert Map containing Emp objects to Json.

Map<Integer, Emp> employees = new HashMap<Integer, Emp>(); 
Emp emp1 = new Emp();
emp1.setId(1);
emp1.setFirstName("Rahul");
emp1.setLastName("Anand");
		
Emp emp2 = new Emp();
emp2.setId(2);
emp2.setFirstName("Daniel");
emp2.setLastName("Anderson");
		
employees.put(1, emp1);
employees.put(2, emp2);
		
Gson gson = new Gson();
String jsonString = gson.toJson(employees);
System.out.println(jsonString);

Map<Integer, Emp> employees = new HashMap<Integer, Emp>();

Emp emp1 = new Emp();

emp1.setId(1);

emp1.setFirstName("Rahul");

emp1.setLastName("Anand");

Emp emp2 = new Emp();

emp2.setId(2);

emp2.setFirstName("Daniel");

emp2.setLastName("Anderson");

employees.put(1, emp1);

employees.put(2, emp2);

Gson gson = new Gson();

String jsonString = gson.toJson(employees);

System.out.println(jsonString);

Output

{"1":{"id":1,"firstName":"Rahul","lastName":"Anand"},"2":{"id":2,"firstName":"Daniel","lastName":"Anderson"}}

1	{"1":{"id":1,"firstName":"Rahul","lastName":"Anand"},"2":{"id":2,"firstName":"Daniel","lastName":"Anderson"}}

Example to convert Json to Map.

String jsonString = "{\"1\":{\"id\":1,\"firstName\":\"Rahul\",\"lastName\":\"Anand\"},\"2\":{\"id\":2,\"firstName\":\"Daniel\",\"lastName\":\"Anderson\"}}";
Gson gson = new Gson();
Type type = new TypeToken<Map<Integer, Emp>>(){}.getType();
Map<Integer, Emp> employees = gson.fromJson(jsonString, type);
System.out.println(employees);

String jsonString = "{\"1\":{\"id\":1,\"firstName\":\"Rahul\",\"lastName\":\"Anand\"},\"2\":{\"id\":2,\"firstName\":\"Daniel\",\"lastName\":\"Anderson\"}}";

Gson gson = new Gson();

Type type = new TypeToken<Map<Integer, Emp>>(){}.getType();

Map<Integer, Emp> employees = gson.fromJson(jsonString, type);

System.out.println(employees);

Json String in user readable format

{
  "1": {
    "id": 1,
    "firstName": "Rahul",
    "lastName": "Anand"
  },
  "2": {
    "id": 2,
    "firstName": "Daniel",
    "lastName": "Anderson"
  }
}

{

"1": {

"id": 1,

"firstName": "Rahul",

"lastName": "Anand"

"2": {

"id": 2,

"firstName": "Daniel",

"lastName": "Anderson"

}

Output

{1=Id : 1, FirstName : Rahul, Last Name : Anand, 2=Id : 2, FirstName : Daniel, Last Name : Anderson}

1	{1=Id : 1, FirstName : Rahul, Last Name : Anand, 2=Id : 2, FirstName : Daniel, Last Name : Anderson}

Stay tuned for more tutorials and examples.

This entry was posted in Java and tagged gson, java.

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