Package jakarta.servlet.http

Interface HttpSession

public interface HttpSession

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

• View and manipulate information about a session, such as the session identifier, creation time, and last accessed time
• Bind objects to sessions, allowing user information to persist across multiple user connections

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.

See Also:

• HttpSessionBindingListener

Method Summary

Modifier and Type	Method	Description
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.
Enumeration<String>	getAttributeNames()	Returns an Enumeration of String objects containing the names of all the objects bound to this session.
long	getCreationTime()	Returns the time when this session was created, measured in milliseconds since midnight January 1, 1970 GMT.
String	getId()	Returns a string containing the unique identifier assigned to this session.
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.
int	getMaxInactiveInterval()	Returns the maximum time interval, in seconds, that the servlet container will keep this session open between client accesses.
ServletContext	getServletContext()	Returns the ServletContext to which this session belongs.
void	invalidate()	Invalidates this session then unbinds any objects bound to it.
boolean	isNew()	Returns true if the client does not yet know about the session or if the client chooses not to join the session.
void	removeAttribute(String name)	Removes the object bound with the specified name from this session.
void	setAttribute(String name, Object value)	Binds an object to this session, using the name specified.
void	setMaxInactiveInterval(int interval)	Specifies the time, in seconds, between client requests before the servlet container will invalidate this session.

Method Details

getCreationTime

long getCreationTime()

Returns the time when this session was created, measured in milliseconds since midnight January 1, 1970 GMT.

Returns:

a long specifying when this session was created, expressed in milliseconds since 1/1/1970 GMT

Throws:

IllegalStateException - if this method is called on an invalidated session

getId

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.

Returns:

a string specifying the identifier assigned to this session

Throws:

IllegalStateException - if this method is called on an invalidated session

getLastAccessedTime

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.

Returns:

a long representing the last time the client sent a request associated with this session, expressed in milliseconds since 1/1/1970 GMT

Throws:

IllegalStateException - if this method is called on an invalidated session

getServletContext

ServletContext getServletContext()

Returns the ServletContext to which this session belongs.

Returns:

The ServletContext object for the web application

Since:

Servlet 2.3

setMaxInactiveInterval

void setMaxInactiveInterval(int interval)

Specifies the time, in seconds, between client requests before the servlet container will invalidate this session. A zero or negative time indicates that the session should never timeout.

Parameters:

interval - An integer specifying the number of seconds

getMaxInactiveInterval

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 zero or negative time indicates that the session should never timeout.

Returns:

an integer specifying the number of seconds this session remains open between client requests

See Also:

• setMaxInactiveInterval(int)

getAttribute

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.

Parameters:

name - a string specifying the name of the object

Returns:

the object with the specified name

Throws:

IllegalStateException - if this method is called on an invalidated session

getAttributeNames

Enumeration<String> getAttributeNames()

Returns an Enumeration of String objects containing the names of all the objects bound to this session.

Returns:

an Enumeration of String objects specifying the names of all the objects bound to this session

Throws:

IllegalStateException - if this method is called on an invalidated session

setAttribute

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().

Parameters:

name - the name to which the object is bound; cannot be null

value - the object to be bound

Throws:

IllegalStateException - if this method is called on an invalidated session

removeAttribute

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.

Parameters:

name - the name of the object to remove from this session

Throws:

IllegalStateException - if this method is called on an invalidated session

invalidate

void invalidate()

Invalidates this session then unbinds any objects bound to it.

Throws:

IllegalStateException - if this method is called on an already invalidated session

isNew

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.

Returns:

true if the server has created a session, but the client has not yet joined

Throws:

IllegalStateException - if this method is called on an already invalidated session