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## javax.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 invalidatd or expired.

When container migrates a session between VMs in a distributed container setting, all session atributes 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`, `HttpSessionContext`

Method Summary
`java.lang.Object` | `getAttribute(java.lang.String name)` Returns the object bound with the specified name in this session, or `null` if no object is bound under the name.
`java.util.Enumeration` | `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.
`java.lang.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 recieved 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.
`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.
`java.lang.Object` | `getValue(java.lang.String name)` Deprecated. As of Version 2.2, this method is replaced by `getAttribute(java.lang.String)`.
`java.lang.String[]` | `getValueNames()` Deprecated. As of Version 2.2, this method is replaced by `getAttributeNames()`
`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` | `putValue(java.lang.String name, java.lang.Object value)` Deprecated. As of Version 2.2, this method is replaced by `setAttribute(java.lang.String, java.lang.Object)`
`void` | `removeAttribute(java.lang.String name)` Removes the object bound with the specified name from this session.
`void` | `removeValue(java.lang.String name)` Deprecated. As of Version 2.2, this method is replaced by `removeAttribute(java.lang.String)`
`void` | `setAttribute(java.lang.String name, java.lang.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 Detail

### getCreationTime

    public 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:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### getId

    public java.lang.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

### getLastAccessedTime

    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 recieved 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

### getServletContext

    public ServletContext getServletContext()

  Returns the ServletContext to which this session belongs.
  Returns:
    The ServletContext object for the web application
  Since:
    2.3

### setMaxInactiveInterval

    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.
  Parameters:
    `interval` - An integer specifying the number of seconds

### getMaxInactiveInterval

    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.
  Returns:
    an integer specifying the number of seconds this session remains open between client requests
  See Also:
    `setMaxInactiveInterval(int)`

### getSessionContext

    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.

### getAttribute

    public java.lang.Object getAttribute(java.lang.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:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### getValue

    public java.lang.Object getValue(java.lang.String name)

  Deprecated. As of Version 2.2, this method is replaced by `getAttribute(java.lang.String)`.

  Parameters:
    `name` - a string specifying the name of the object
  Returns:
    the object with the specified name
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### getAttributeNames

    public java.util.Enumeration 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:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### getValueNames

    public java.lang.String[] getValueNames()

  Deprecated. As of Version 2.2, this method is replaced by `getAttributeNames()`

  Returns:
    an array of `String` objects specifying the names of all the objects bound to this session
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### setAttribute

    public void setAttribute(java.lang.String name,
                             java.lang.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 `HttpSessionAttributeListener`s 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:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### putValue

    public void putValue(java.lang.String name,
                         java.lang.Object value)

  Deprecated. As of Version 2.2, this method is replaced by `setAttribute(java.lang.String, java.lang.Object)`

  Parameters:
    `name` - the name to which the object is bound; cannot be null
    `value` - the object to be bound; cannot be null
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### removeAttribute

    public void removeAttribute(java.lang.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 `HttpSessionAttributeListener`s in the web application.

  Parameters:
    `name` - the name of the object to remove from this session
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### removeValue

    public void removeValue(java.lang.String name)

  Deprecated. As of Version 2.2, this method is replaced by `removeAttribute(java.lang.String)`

  Parameters:
    `name` - the name of the object to remove from this session
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an invalidated session

### invalidate

    public void invalidate()

  Invalidates this session then unbinds any objects bound to it.
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an already invalidated session

### isNew

    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.
  Returns:
    `true` if the server has created a session, but the client has not yet joined
  Throws:
    `java.lang.IllegalStateException` - if this method is called on an already invalidated session

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