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package org.eclipse.jetty.server.session;

import java.util.Set;
import javax.servlet.http.HttpServletRequest;

import org.eclipse.jetty.util.component.LifeCycle;

SessionCache A working set of Session objects for a context. Ideally, multiple requests for the same session id in the same context will always share the same Session object from the SessionCache, but it would be possible for implementations of SessionCache to create a fresh object for each request. The SessionData pertaining to the Session objects is obtained from/written to a SessionDataStore. The SessionDataStore is the authoritative source of session data: 

if the session data is not present in the SessionDataStore the session does not exist.
if the session data is present in the SessionDataStore but its expiry time has passed then
the session is deemed to have expired and is therefore invalid

A SessionCache can passivate a valid Session to the SessionDataStore and
evict it from the cache according to various strategies:

whenever the last request exits a Session
whenever the Session has not been accessed for a configurable number of seconds
.
Eviction can save memory, and can also help mitigate
some of the problems of a non-sticky load balancer by forcing the session data to
be re-read from the SessionDataStore more frequently.
/**
 * SessionCache
 *
 * A working set of {@link Session} objects for a context.
 *
 * Ideally, multiple requests for the same session id in the same context will always
 * share the same Session object from the SessionCache, but it would be possible
 * for implementations of SessionCache to create a fresh object for each request.
 *
 * The SessionData pertaining to the Session objects is obtained from/written to a SessionDataStore.
 * The SessionDataStore is the authoritative source of session data:
 * <ul>
 * <li>if the session data is not present in the SessionDataStore the session does not exist.</li>
 * <li>if the session data is present in the SessionDataStore but its expiry time has passed then
 * the session is deemed to have expired and is therefore invalid</li>
 * </ul>
 *
 * A SessionCache can passivate a valid Session to the SessionDataStore and
 * evict it from the cache according to various strategies:
 * <ul>
 * <li>whenever the last request exits a Session</li>
 * <li>whenever the Session has not been accessed for a configurable number of seconds</li>
 * </ul>.
 *
 * Eviction can save memory, and can also help mitigate
 * some of the problems of a non-sticky load balancer by forcing the session data to
 * be re-read from the SessionDataStore more frequently.
 */
public interface SessionCache extends LifeCycle
{
    public static final int NEVER_EVICT = -1;
    public static final int EVICT_ON_SESSION_EXIT = 0;
    public static final int EVICT_ON_INACTIVITY = 1; //any number equal or greater is time in seconds

    
Params:
context – the SessionContext to use for this cache/**
     * @param context the {@link SessionContext} to use for this cache
     */
    void initialize(SessionContext context);

    void shutdown();

    SessionHandler getSessionHandler();

    
Create an entirely new Session.
Params:
request – the request
id – the unique id associated to the session
time – the timestamp of the session creation
maxInactiveMs – the max inactive time in milliseconds
Returns:
a new Session/**
     * Create an entirely new Session.
     *
     * @param request the request
     * @param id the unique id associated to the session
     * @param time the timestamp of the session creation
     * @param maxInactiveMs the max inactive time in milliseconds
     * @return a new Session
     */
    Session newSession(HttpServletRequest request, String id, long time, long maxInactiveMs);

    
Re-materialize a Session that has previously existed.
Params:
data – the data associated with the session
Returns:
a Session object for the data supplied/**
     * Re-materialize a Session that has previously existed.
     *
     * @param data the data associated with the session
     * @return a Session object for the data supplied
     */
    Session newSession(SessionData data);

    
Change the id of a Session.
Params:
oldId – the current session id
newId – the new session id
oldExtendedId – the current extended session id
newExtendedId – the new extended session id
Throws:
Exception – if any error occurred
Returns:
the Session after changing its id/**
     * Change the id of a Session.
     *
     * @param oldId the current session id
     * @param newId the new session id
     * @param oldExtendedId the current extended session id
     * @param newExtendedId the new extended session id
     * @return the Session after changing its id
     * @throws Exception if any error occurred
     */
    Session renewSessionId(String oldId, String newId, String oldExtendedId, String newExtendedId) throws Exception;

    
Get an existing Session. If necessary, the cache will load the data for
the session from the configured SessionDataStore.
Params:
id – the session id
Throws:
Exception – if any error occurred
Returns:
the Session if one exists, null otherwise/**
     * Get an existing Session. If necessary, the cache will load the data for
     * the session from the configured SessionDataStore.
     *
     * @param id the session id
     * @return the Session if one exists, null otherwise
     * @throws Exception if any error occurred
     */
    Session get(String id) throws Exception;

    
Finish using a Session. This is called by the SessionHandler
once a request is finished with a Session. SessionCache
implementations may want to delay writing out Session contents
until the last request exits a Session.
Params:
id – the session id
session – the current session object
Throws:
Exception – if any error occurred/**
     * Finish using a Session. This is called by the SessionHandler
     * once a request is finished with a Session. SessionCache
     * implementations may want to delay writing out Session contents
     * until the last request exits a Session.
     *
     * @param id the session id
     * @param session the current session object
     * @throws Exception if any error occurred
     */
    void put(String id, Session session) throws Exception;

    
Check to see if a Session is in the cache. Does NOT consult
the SessionDataStore.
Params:
id – the session id
Throws:
Exception – if any error occurred
Returns:
true if a Session object matching the id is present
in the cache, false otherwise/**
     * Check to see if a Session is in the cache. Does NOT consult
     * the SessionDataStore.
     *
     * @param id the session id
     * @return true if a Session object matching the id is present
     * in the cache, false otherwise
     * @throws Exception if any error occurred
     */
    boolean contains(String id) throws Exception;

    
Check to see if a session exists: WILL consult the
SessionDataStore.
Params:
id – the session id
Throws:
Exception – if any error occurred
Returns:
true if the session exists, false otherwise/**
     * Check to see if a session exists: WILL consult the
     * SessionDataStore.
     *
     * @param id the session id
     * @return true if the session exists, false otherwise
     * @throws Exception if any error occurred
     */
    boolean exists(String id) throws Exception;

    
Remove a Session completely: from both this
cache and the SessionDataStore.
Params:
id – the session id
Throws:
Exception – if any error occurred
Returns:
the Session that was removed, null otherwise/**
     * Remove a Session completely: from both this
     * cache and the SessionDataStore.
     *
     * @param id the session id
     * @return the Session that was removed, null otherwise
     * @throws Exception if any error occurred
     */
    Session delete(String id) throws Exception;

    
Check a list of session ids that belong to potentially expired
sessions. The Session in the cache should be checked,
but also the SessionDataStore, as that is the authoritative
source of all session information.
Params:
candidates – the session ids to check
Returns:
the set of session ids that have actually expired: this can
be a superset of the original candidate list./**
     * Check a list of session ids that belong to potentially expired
     * sessions. The Session in the cache should be checked,
     * but also the SessionDataStore, as that is the authoritative
     * source of all session information.
     *
     * @param candidates the session ids to check
     * @return the set of session ids that have actually expired: this can
     * be a superset of the original candidate list.
     */
    Set<String> checkExpiration(Set<String> candidates);

    
Check a Session to see if it might be appropriate to
evict or expire.
Params:
session – the session to check/**
     * Check a Session to see if it might be appropriate to
     * evict or expire.
     *
     * @param session the session to check
     */
    void checkInactiveSession(Session session);

    
A SessionDataStore that is the authoritative source
of session information.
Params:
sds – the SessionDataStore to use/**
     * A SessionDataStore that is the authoritative source
     * of session information.
     *
     * @param sds the {@link SessionDataStore} to use
     */
    void setSessionDataStore(SessionDataStore sds);

    
Returns:
the SessionDataStore used/**
     * @return the {@link SessionDataStore} used
     */
    SessionDataStore getSessionDataStore();

    
Sessions in this cache can be:

never evicted
evicted once the last request exits
evicted after a configurable period of inactivity

Params:
policy – -1 is never evict; 0 is evict-on-exit; and any other positive
value is the time in seconds that a session can be idle before it can
be evicted./**
     * Sessions in this cache can be:
     * <ul>
     * <li>never evicted</li>
     * <li>evicted once the last request exits</li>
     * <li>evicted after a configurable period of inactivity</li>
     * </ul>
     *
     * @param policy -1 is never evict; 0 is evict-on-exit; and any other positive
     * value is the time in seconds that a session can be idle before it can
     * be evicted.
     */
    void setEvictionPolicy(int policy);

    
Returns:
the eviction policy/**
     * @return the eviction policy
     */
    int getEvictionPolicy();

    
Whether or not a a session that is about to be evicted should
be saved before being evicted.
Params:
saveOnEvict – true if the session should be saved before being evicted/**
     * Whether or not a a session that is about to be evicted should
     * be saved before being evicted.
     *
     * @param saveOnEvict <code>true</code> if the session should be saved before being evicted
     */
    void setSaveOnInactiveEviction(boolean saveOnEvict);

    
Returns:
true if the session should be saved before being evicted/**
     * @return <code>true</code> if the session should be saved before being evicted
     */
    boolean isSaveOnInactiveEviction();

    
Whether or not a session that is newly created should be
immediately saved. If false, a session that is created and
invalidated within a single request is never persisted.
Params:
saveOnCreate – true to immediately save the newly created session/**
     * Whether or not a session that is newly created should be
     * immediately saved. If false, a session that is created and
     * invalidated within a single request is never persisted.
     *
     * @param saveOnCreate <code>true</code> to immediately save the newly created session
     */
    void setSaveOnCreate(boolean saveOnCreate);

    
Returns:
if true the newly created session will be saved immediately/**
     * @return if <code>true</code> the newly created session will be saved immediately
     */
    boolean isSaveOnCreate();

    
If the data for a session exists but is unreadable,
the SessionCache can instruct the SessionDataStore to delete it.
Params:
removeUnloadableSessions – true to delete session which cannot be loaded/**
     * If the data for a session exists but is unreadable,
     * the SessionCache can instruct the SessionDataStore to delete it.
     *
     * @param removeUnloadableSessions <code>true</code> to delete session which cannot be loaded
     */
    void setRemoveUnloadableSessions(boolean removeUnloadableSessions);

    
Returns:
if true unloadable session will be deleted/**
     * @return if <code>true</code> unloadable session will be deleted
     */
    boolean isRemoveUnloadableSessions();
}