如何获取session.setAttribute

Question

我这样创建HttpSession容器:

@SessionScoped
@ManagedBean(name="userManager")
public class UserManager extends Tools
{
  /* [private variables] */
  ...
  public String login() 
  {
    /* [find user] */
    ...
    FacesContext context = FacesContext.getCurrentInstance();
    session = (HttpSession) context.getExternalContext().getSession(true);
    session.setAttribute("id", user.getID());
    session.setAttribute("username", user.getName());
    ...
    System.out.println("Session id: " + session.getId());

我有SessionListener它应该给我关于创建的会话的信息:

@WebListener
public class SessionListener implements HttpSessionListener
{
  @Override
  public void sessionCreated(HttpSessionEvent event) {    
    HttpSession session = event.getSession();
    System.out.println("Session id: " + session.getId());
    System.out.println("New session: " + session.isNew());
    ...
  }
}

如何获取username属性?

如果我尝试使用System.out.println("User name: " + session.getAttribute("username"))它抛出java.lang.NullPointerException ..

Answer 1

HttpSessionListener接口用于监视何时在应用服务器上创建和销毁会话。HttpSessionEvent.getSession()返回一个新创建或销毁的会话(取决于它是否分别由sessionCreated/sessionDestroyed调用)。

如果你想要一个现有的会话，你必须从请求中获取会话。

HttpSession session = request.getSession(true).
String username = (String)session.getAttribute("username");

Answer 2

如果找到给定的键，则session.getAttribute("key")返回java.lang.Object类型的值。否则返回null。

String userName=(String)session.getAttribute("username");
if(userName!=null)
{
  System.out.println("User name: " + userName);
}