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

@Entity
public class User {

@Id
private int id;
private String name;
private int age;

public User() {
}

public User(int id, String name, int age) {
    this.id = id;
    this.name = name;
    this.age = age;
}

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 getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;

import java.util.List;

@Controller
public class UserController {

@Autowired
private UserService userService;

@RequestMapping(value = "/")
public String display(ModelMap modelMap){
    User user = new User(1, "Endriyas", 21);
    userService.addUser(user);
    List<User> users = userService.getAllUser();
    modelMap.put("users", users);
    return "users";
}

}

<div>
    <form action="#" th:action="@{/}" th:object="${users}" method="post">
        <div>
            <label>
                <span>ID</span>
            </label>
            <input type="number" th:field="*{id}"/>
        </div>
        <div>
            <label>
                <span>Name</span>
            </label>
            <input type="text" th:field="*{name}"/>
        </div>
        <div>
            <label>
                <span>Age</span>
            </label>
            <input type="number" th:field="*{age}"/>
        </div>
        <div>
            <button type="submit" name="save">SAVE</button>
        </div>
    </form>
</div>