save
findOne
exists
findAll
count
delete
deleteAll

package ua.samuliak.messenger.entity;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;

@Entity
@Table(name = ""user"")
public class User {

    @Id
    @GeneratedValue(generator = "increment")
    @GenericGenerator(name = "increment", strategy = "increment")
    private long id;

    @Column(nullable = false, length = 20)
    private String login;

    @Column(nullable = false, length = 20)
    private String password;

    @Column(length = 2)
    private String country;

    @ManyToOne(fetch = FetchType.EAGER, cascade = {CascadeType.MERGE, CascadeType.PERSIST})
    @JoinColumn(name = "room_id")
    private Room room;

    public Room getRoom() {
        return room;
    }

    public void setRoom(Room room) {
        this.room = room;
    }

    public User() {}

    public long getId() {
        return id;
    }

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

    public String getLogin() {
        return login;
    }

    public void setLogin(String login) {
        this.login = login;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }
}

.....
    @RequestMapping(value = "/user/{name}", method = RequestMethod.GET)
    @ResponseBody
    public User getUserByName(@PathVariable("name") String userLogin){
        return userService.getByLogin(userLogin);
    }
.....

package ua.samuliak.messenger.repository;


import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import ua.samuliak.messenger.entity.User;

public interface UserRepository extends JpaRepository<User, Long>{
    @Query("FROM User WHERE login = :name ")
    User findByName(String name);
}