In this post under Gson. I will show how to deserialize a JSON data back to Java object using Gson framework.

For our example I will use the below json data. The json data contains employee information.

employee.json


{"id":1,"name":"employee1","ssn":1234}

The class structure of Employee is as shown below

Employee class


public class Employee {
    private int id;
    private String name;
    private int ssn;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getSsn() {
        return ssn;
    }

    public void setSsn(int ssn) {
        this.ssn = ssn;
    }
    
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("Id:" + id).append("\n");
        sb.append("Name:" + name).append("\n");
        sb.append("ssn: " + ssn);
        
        return sb.toString();
    }
}

Below is the complete code

Main Code


1  import java.io.File;
2  import java.io.FileReader;
3  import java.io.IOException;
4  
5  import com.google.gson.Gson;
6  
7  public class GsonDemo2 {
8   public static void main(String[] args) {
9       File file = new File("employee.json");
10      Gson gson = new Gson();
11      try (FileReader fr = new FileReader(file)) {
12          Employee employee = gson.fromJson(fr, Employee.class);
13          System.out.println(employee);
14      } catch (IOException excep) {
15          excep.printStackTrace();
16      }
17  }
18 }

At line 9, I create a file object representing the file “employee.json”.

At line 10, I create a Gson instance “gson”.

At line 12, I deserialize the content in employee.json file to employee object by calling “fromJson” mehtod.

It takes two arguments
1) the FileReader object to read the file
2) the target class type