//session给用户一种标志，让用户可以在不同页面以及网站中都有一个特殊的标记
public interface HttpSession {
    /**
     * Returns the time when this session was created, measured
     * in milliseconds since midnight January 1, 1970 GMT.
     * @return            a <code>long</code> specifying
     *  when this session was created, expressed in  milliseconds since 1/1/1970 GMT
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
   //session创建时间
    public long getCreationTime();
    /**
     * Returns a string containing the unique identifier assigned 
     * to this session. The identifier is assigned 
     * by the servlet container and is implementation dependent.
     * @return            a string specifying the identifier
     *              assigned to this session
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    //session id
    public String getId();
    /**
     * Returns the last time the client sent a request associated with
     * this session, as the number of milliseconds since midnight
     * January 1, 1970 GMT, and marked by the time the container received the request. 
     * <p>Actions that your application takes, such as getting or setting
     * a value associated with the session, do not affect the access time.
     * @return            a <code>long</code>
     *              representing the last time 
     *              the client sent a request associated
     *              with this session, expressed in 
     *              milliseconds since 1/1/1970 GMT
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    //最近一次客户端发送与这个session相关联的请求的时间
    public long getLastAccessedTime();
    /**
    * Returns the ServletContext to which this session belongs.
    * @return The ServletContext object for the web application
    * @since 2.3
    */
    //session所属于的ServletContext
    public ServletContext getServletContext();
    /**
     * Specifies the time, in seconds, between client requests before the 
     * servlet container will invalidate this session.  A negative time
     * indicates the session should never timeout.
     * @param interval    An integer specifying the number of seconds 
     */
    //session失效时间
    public void setMaxInactiveInterval(int interval);
   /**
    * Returns the maximum time interval, in seconds, that 
    * the servlet container will keep this session open between 
    * client accesses. After this interval, the servlet container
    * will invalidate the session.  The maximum time interval can be set
    * with the <code>setMaxInactiveInterval</code> method.
    * A negative time indicates the session should never timeout.
    * @return      an integer specifying the number of
    *        seconds this session remains open
    *        between client requests
    * @see      #setMaxInactiveInterval
    */
    //获得失效时间
    public int getMaxInactiveInterval();
   /**
    * @deprecated  As of Version 2.1, this method is
    *        deprecated and has no replacement.
    *        It will be removed in a future
    *        version of the Java Servlet API.
    */

    public HttpSessionContext getSessionContext();
    /**
     * Returns the object bound with the specified name in this session, or
     * <code>null</code> if no object is bound under the name.
     * @param name     a string specifying the name of the object
     * @return         the object with the specified name
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    //session中name的对象
    public Object getAttribute(String name);
    /**
     * @deprecated  As of Version 2.2, this method is
     *        replaced by {@link #getAttribute}.
     * @param name     a string specifying the name of the object
     * @return         the object with the specified name
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
  
    public Object getValue(String name);
    /**
     * Returns an <code>Enumeration</code> of <code>String</code> objects
     * containing the names of all the objects bound to this session. 
     * @return         an <code>Enumeration</code> of 
     *           <code>String</code> objects specifying the
     *           names of all the objects bound to
     *           this session
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    //获得所有属性的枚举
    public Enumeration getAttributeNames();
    /**
     * @deprecated  As of Version 2.2, this method is
     *        replaced by {@link #getAttributeNames}
     * @return            an array of <code>String</code>
     *              objects specifying the
     *              names of all the objects bound to
     *              this session
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    
    public String[] getValueNames();
    /**
     * Binds an object to this session, using the name specified.
     * If an object of the same name is already bound to the session,
     * the object is replaced.
     * <p>After this method executes, and if the new object
     * implements <code>HttpSessionBindingListener</code>,
     * the container calls 
     * <code>HttpSessionBindingListener.valueBound</code>. The container then   
     * notifies any <code>HttpSessionAttributeListener</code>s in the web 
     * application.
     * <p>If an object was already bound to this session of this name
     * that implements <code>HttpSessionBindingListener</code>, its 
     * <code>HttpSessionBindingListener.valueUnbound</code> method is called.
     * <p>If the value passed in is null, this has the same effect as calling 
     * <code>removeAttribute()<code>.
     * @param name        the name to which the object is bound;
     *              cannot be null
     * @param value       the object to be bound
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    //设置属性
    public void setAttribute(String name, Object value);
    /**
     *
     * @deprecated  As of Version 2.2, this method is
     *        replaced by {@link #setAttribute}
     *
     * @param name        the name to which the object is bound;
     *              cannot be null
     *
     * @param value       the object to be bound; cannot be null
     *
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     *
     */
    public void putValue(String name, Object value);
    /**
     * Removes the object bound with the specified name from
     * this session. If the session does not have an object
     * bound with the specified name, this method does nothing.
     * <p>After this method executes, and if the object
     * implements <code>HttpSessionBindingListener</code>,
     * the container calls 
     * <code>HttpSessionBindingListener.valueUnbound</code>. The container
     * then notifies any <code>HttpSessionAttributeListener</code>s in the web 
     * application.
     * @param name           the name of the object to
     *                 remove from this session
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    //删除属性
    public void removeAttribute(String name);
    /**
     * @deprecated  As of Version 2.2, this method is
     *        replaced by {@link #removeAttribute}
     * @param name           the name of the object to
     *                 remove from this session
     * @exception IllegalStateException  if this method is called on an
     *              invalidated session
     */
    public void removeValue(String name);
    /**
     * Invalidates this session then unbinds any objects bound
     * to it. 
     * @exception IllegalStateException  if this method is called on an
     *              already invalidated session
     */
    //session无效
    public void invalidate();
    /**
     * Returns <code>true</code> if the client does not yet know about the
     * session or if the client chooses not to join the session.  For 
     * example, if the server used only cookie-based sessions, and
     * the client had disabled the use of cookies, then a session would
     * be new on each request.
     * @return            <code>true</code> if the 
     *              server has created a session, 
     *              but the client has not yet joined
     * @exception IllegalStateException  if this method is called on an
     *              already invalidated session
     */
    //
    public boolean isNew();
}