Struts 2 - é possível usar set / construtor private?

public class User implements Serializable 
{

	private static final long serialVersionUID = 1L;
	private Integer id;
	private String username;
	private String password;
	
	
	
	/**
	 * @param id
	 * @param username
	 * @param password
	 */
	public User(Integer id, String username, String password) throws Exception
	{
		super();
		this.setId(id);
		this.setUsername(username);
		this.setPassword(password);
	}


	/**
	 * @param id the id to set
	 */
	private void setId(Integer id) 
	{
		if (id < 0)
			throw new IllegalArgumentException("O atributo 'id' não pode ser menor que 0 (Zero) ( id : " + id + ") ");
		
		this.id = id;
	}


	/**
	 * @param username the username to set
	 */
	private void setUsername(String username) throws Exception
	{
		if (username == null)
			throw new NullPointerException("O atributo 'username' é nulo ( Class User : Method setUsername() )");
		
		if (username.trim().isEmpty())
			throw new IllegalArgumentException("O atributo 'username' está vazio ( Class User : Method setUsername() )");
		
		if (username.trim().length() > 20)	
			throw new IllegalArgumentException("O atributo 'username' possui mais de 20 caracteres. username.length : "+ username.length() +" ( Class User : Method setUsername() ) ");
			
		this.username = username.trim();
	}


	/**
	 * @param password the password to set
	 */
	private void setPassword(String password) throws Exception
	{
		if (password == null)
			throw new NullPointerException("O atributo 'password' é nulo ( Class User : Method setPassword() )");
			
		if (password.isEmpty())
			throw new IllegalArgumentException("O atributo 'password' está vazio ( Class User : Method setPassword() )");			
			
		if (password.trim().length() != 8)	
			throw new IllegalArgumentException("O atributo 'password' deve possuir 8 caracteres. password.length : "+ password.length() +" ( Class User : Method setPassword() ) ");
		
		this.password = password.trim();
	}


	/**
	 * @return the id
	 */
	public Integer getId() 
	{return id;}


	/**
	 * @return the username
	 */
	public String getUsername() 
	{return username;}


	/**
	 * @return the password
	 */
	public String getPassword() 
	{return password;}
}

package net.roseindia;
import com.opensymphony.xwork2.ActionSupport;
import java.util.Date;


/**
 * <p> Validate a user login. </p>
 */
public  class Login  extends ActionSupport {


    @Override
    public String execute() throws Exception {
       System.out.println("Validating login");
		if(!getUsername().equals("WilliamSilva") || !getPassword().equals("fly2007")){
           addActionError("Nome ou Password inválido! por favor repita a operação...!");
            return ERROR;
		}else{
			return SUCCESS;
		}
	}


    // ---- Username property ----

    /**
     * <p>Field to store User username.</p>
     * <p/>
     */
    private String username = null;


    /**
     * <p>Provide User username.</p>
     *
     * @return Returns the User username.
     */
    public String getUsername() {
        return username;
    }

    /**
     * <p>Store new User username</p>
     *
     * @param value The username to set.
     */
    public void setUsername(String value) {
        username = value;
    }

    // ---- Username property ----

    /**
     * <p>Field to store User password.</p>
     * <p/>
     */
    private String password = null;


    /**
     * <p>Provide User password.</p>
     *
     * @return Returns the User password.
     */
    public String getPassword() {
        return password;
    }

    /**
     * <p>Store new User password</p>
     *
     * @param value The password to set.
     */
    public void setPassword(String value) {
        password = value;
    }

}