Spring serializing entity returns junk value for timestamp

I'm new to Spring, so I apologize if the question is basic.

I'm writing an application which fetches data from postgres and returns as JSON. The table structure is as below:

table student{
id int,
created_time Timestamp
}

I have an entry in the table as:

 id | created_time           
 ---+---------------------------
 1  | 2015-02-19 23:58:23.579761

I'm having my entity object as:

package main.java;
import java.sql.Timestamp;

import javax.persistence.Entity;
import javax.persistence.Id;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

@Entity
@JsonIgnoreProperties(ignoreUnknown = true)
public class Student {
    @Id
    protected int id;
    protected Timestamp created_time;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public Timestamp getCreated_time() {
        return created_time;
    }
    public void setCreated_time(Timestamp created_time) {
        this.created_time = created_time;
    }

}

And this is how I'm returning the data:

@RestController
@RequestMapping(value = "/student", produces = MediaType.APPLICATION_JSON_VALUE)
public class StudentController {

    @Autowired
    protected StudentRepository studentRepository;

    @RequestMapping(value = "/{id}")
    public Student student(@PathVariable int id) {
        return studentRepository.findOne(id);// uses the findOne() method inherited from CrudRepository
    }

However, the json I get is:

{"id":1,"created_time":1424419103579}

Why is it returning junk value for time stamp? How do I get the original value in same format as is in the table?

Thanks in advance.