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javax.servlet.http
public interface: HttpSession [javadoc | source] Provides a way to identify a user across more than one page request or visit to a Web site and to store information about that user.

The servlet container uses this interface to create a session between an HTTP client and an HTTP server. The session persists for a specified time period, across more than one connection or page request from the user. A session usually corresponds to one user, who may visit a site many times. The server can maintain a session in many ways such as using cookies or rewriting URLs.

This interface allows servlets to

When an application stores an object in or removes an object from a session, the session checks whether the object implements HttpSessionBindingListener . If it does, the servlet notifies the object that it has been bound to or unbound from the session. Notifications are sent after the binding methods complete. For session that are invalidated or expire, notifications are sent after the session has been invalidated or expired.

When container migrates a session between VMs in a distributed container setting, all session attributes implementing the HttpSessionActivationListener interface are notified.

A servlet should be able to handle cases in which the client does not choose to join a session, such as when cookies are intentionally turned off. Until the client joins the session, isNew returns true. If the client chooses not to join the session, getSession will return a different session on each request, and isNew will always return true.

Session information is scoped only to the current web application (ServletContext), so information stored in one context will not be directly visible in another.

Method from javax.servlet.http.HttpSession Summary:
getAttribute,   getAttributeNames,   getCreationTime,   getId,   getLastAccessedTime,   getMaxInactiveInterval,   getServletContext,   getSessionContext,   getValue,   getValueNames,   invalidate,   isNew,   putValue,   removeAttribute,   removeValue,   setAttribute,   setMaxInactiveInterval
Method from javax.servlet.http.HttpSession Detail:
 public Object getAttribute(String name)
    Returns the object bound with the specified name in this session, or null if no object is bound under the name.
 public Enumeration getAttributeNames()
    Returns an Enumeration of String objects containing the names of all the objects bound to this session.
 public long getCreationTime()
    Returns the time when this session was created, measured in milliseconds since midnight January 1, 1970 GMT.
 public String getId()
    Returns a string containing the unique identifier assigned to this session. The identifier is assigned by the servlet container and is implementation dependent.
 public long getLastAccessedTime()
    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.

    Actions that your application takes, such as getting or setting a value associated with the session, do not affect the access time.

 public int getMaxInactiveInterval()
    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 setMaxInactiveInterval method. A negative time indicates the session should never timeout.
 public ServletContext getServletContext()
    Returns the ServletContext to which this session belongs.
 public HttpSessionContext getSessionContext()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 Object getValue(String name)Deprecated! As -  of Version 2.2, this method is
			replaced by #getAttribute .

 public String[] getValueNames()Deprecated! As -  of Version 2.2, this method is
			replaced by #getAttributeNames 

 public  void invalidate()
    Invalidates this session then unbinds any objects bound to it.
 public boolean isNew()
    Returns true 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.
 public  void putValue(String name,
    Object value)Deprecated! As -  of Version 2.2, this method is
			replaced by #setAttribute 

 public  void removeAttribute(String name)
    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.

    After this method executes, and if the object implements HttpSessionBindingListener, the container calls HttpSessionBindingListener.valueUnbound. The container then notifies any HttpSessionAttributeListeners in the web application.

 public  void removeValue(String name)Deprecated! As -  of Version 2.2, this method is
			replaced by #removeAttribute 

 public  void setAttribute(String name,
    Object value)
    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.

    After this method executes, and if the new object implements HttpSessionBindingListener, the container calls HttpSessionBindingListener.valueBound. The container then notifies any HttpSessionAttributeListeners in the web application.

    If an object was already bound to this session of this name that implements HttpSessionBindingListener, its HttpSessionBindingListener.valueUnbound method is called.

    If the value passed in is null, this has the same effect as calling removeAttribute().

 public  void setMaxInactiveInterval(int interval)
    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.