/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package javax.servlet.http;

import java.util.Enumeration;

import javax.servlet.ServletContext;

/**
 * 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.
 * <p>
 * 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.
 * <p>
 * This interface allows servlets to
 * <ul>
 * <li>View and manipulate information about a session, such as the session identifier, creation time, and last accessed
 * time
 * <li>Bind objects to sessions, allowing user information to persist across multiple user connections
 * </ul>
 * <p>
 * When an application stores an object in or removes an object from a session, the session checks whether the object
 * implements {@link 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.
 * <p>
 * When container migrates a session between VMs in a distributed container setting, all session attributes implementing
 * the {@link HttpSessionActivationListener} interface are notified.
 * <p>
 * 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, <code>isNew</code> returns <code>true</code>. If
 * the client chooses not to join the session, <code>getSession</code> will return a different session on each request,
 * and <code>isNew</code> will always return <code>true</code>.
 * <p>
 * Session information is scoped only to the current web application ( <code>ServletContext</code>), so information
 * stored in one context will not be directly visible in another.
 *
 * @see HttpSessionBindingListener
 */
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
     */
    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
     */
    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
     */
    long getLastAccessedTime();

    /**
     * Returns the ServletContext to which this session belongs.
     *
     * @return The ServletContext object for the web application
     *
     * @since Servlet 2.3
     */
    ServletContext getServletContext();

    /**
     * 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.
     *
     * @param interval An integer specifying the number of seconds
     */
    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 zero or negative time indicates that
     * the session should never timeout.
     *
     * @return an integer specifying the number of seconds this session remains open between client requests
     *
     * @see #setMaxInactiveInterval
     */
    int getMaxInactiveInterval();

    /**
     * Do not use.
     *
     * @return A dummy implementation of HttpSessionContext
     *
     * @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.
     */
    @Deprecated
    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
     */
    Object getAttribute(String 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
     *
     * @deprecated As of Version 2.2, this method is replaced by {@link #getAttribute}.
     */
    @Deprecated
    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
     */
    Enumeration<String> 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
     *
     * @deprecated As of Version 2.2, this method is replaced by {@link #getAttributeNames}
     */
    @Deprecated
    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
     */
    void setAttribute(String name, Object value);

    /**
     * @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
     *
     * @deprecated As of Version 2.2, this method is replaced by {@link #setAttribute}
     */
    @Deprecated
    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
     */
    void removeAttribute(String name);

    /**
     * @param name the name of the object to remove from this session
     *
     * @exception IllegalStateException if this method is called on an invalidated session
     *
     * @deprecated As of Version 2.2, this method is replaced by {@link #removeAttribute}
     */
    @Deprecated
    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
     */
    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
     */
    boolean isNew();
}
