public String save() {

    boolean isDatavalid = validateData();

    if (isDatavalid) {

                    //clearRoles remove all user roles
        userService.clearRoles(selectedUser);
        List<UserRole> roles= userService.assignRolesToUser(selectedUser, rolesToAdd);
        selectedUser.setRoles(roles);
        userService.updateUser(selectedUser);
        manageFormsVisibility(true, false, false);
    }

    return null;
}

public List<UserRole> assignRolesToUser(User user, List<Role> roles) {
    List<UserRole> userRoles = new ArrayList<UserRole>();

    for(Role r:roles){

        UserRole role = new UserRole(user, r);
        userRoles.add(role);
        em.persist(role);
    }
    return userRoles;

}

@Entity
public class User implements Serializable {
    //other properties

private List<UserRole> roles = new ArrayList<UserRole>();

@OneToMany(mappedBy = "user", cascade = CascadeType.REMOVE)
public List<UserRole> getRoles() {
    roles.size();
    return roles;
}
}

@Entity
public class Role implements Serializable {
 //other properties

private List<UserRole> users = new ArrayList<UserRole>();

@OneToMany(mappedBy = "role", cascade = CascadeType.REMOVE)
public List<UserRole> getUsers() {
    users.size();
    return users;
}
}

@Entity
 @Table(name="User_Role")

 public class UserRole implements Serializable {

private IdUserRole idUserRole = new IdUserRole();
private Date activationDate;
private Date deactivationDate;
private User user;
private Role role;
private static final long serialVersionUID = 1L;

public UserRole() {
    super();
}

@EmbeddedId
public IdUserRole getIdUserRole() {
    return this.idUserRole;
}

public void setIdUserRole(IdUserRole idUserRole) {
    this.idUserRole = idUserRole;
}

@Temporal(TemporalType.DATE)
public Date getActivationDate() {
    return this.activationDate;
}

public void setActivationDate(Date activationDate) {
    this.activationDate = activationDate;
}

@Temporal(TemporalType.DATE)
public Date getDeactivationDate() {
    return this.deactivationDate;
}

public void setDeactivationDate(Date deactivationDate) {
    this.deactivationDate = deactivationDate;
}

public void setUser(User user) {
    this.user = user;
}

@ManyToOne
@JoinColumn(name = "user_id", insertable = false, updatable = false)
public User getUser() {
    return user;
}

public void setRole(Role role) {
    this.role = role;
}

@ManyToOne
@JoinColumn(name = "role_id", insertable = false, updatable = false)
public Role getRole() {
    return role;
}

public UserRole(User user, Role role) {
    getIdUserRole().setRoleId(role.getRoleId());
    getIdUserRole().setUserId(user.getUserId());
    this.setUser(user);
    this.setRole(role);
    user.getRoles().add(this);
    role.getUsers().add(this);
}
}