分布式共享Session之SpringSession源码细节

//包装
HttpServletRequest strategyRequest = this.httpSessionStrategy
		.wrapRequest(wrappedRequest, wrappedResponse);
//再包装
HttpServletResponse strategyResponse = this.httpSessionStrategy
		.wrapResponse(wrappedRequest, wrappedResponse);

try {
	filterChain.doFilter(strategyRequest, strategyResponse);
}
finally {
   // 提交
	wrappedRequest.commitSession();
}

@Override
protected void onResponseCommitted() {
	this.request.commitSession();
}

@Override
public HttpSessionWrapper getSession(boolean create) {
	// currentSession 是存在 request 的 attribute 中
	HttpSessionWrapper currentSession = getCurrentSession();
	// 存在即返回
	if (currentSession != null) {
		return currentSession;
	}
	// 获取请求的 sessionId, Cookie策略的话从cookie里拿, header策略的话在 Http Head 中获取
	String requestedSessionId = getRequestedSessionId();
	// 如果获取到，并且没有‘sessionId失效’标识
	if (requestedSessionId != null
			&& getAttribute(INVALID_SESSION_ID_ATTR) == null) {
		// 这里是从 repository 中读取，如 RedisRepository
		S session = getSession(requestedSessionId);
		// 读取到了就恢复出session
		if (session != null) {
			this.requestedSessionIdValid = true;
			currentSession = new HttpSessionWrapper(session, getServletContext());
			currentSession.setNew(false);
			setCurrentSession(currentSession);
			return currentSession;
		}
		// 没有读取到（过期了）, 设置‘失效’标识, 下次不用再去 repository 中读取
		else {
			// This is an invalid session id. No need to ask again if
			// request.getSession is invoked for the duration of this request
			if (SESSION_LOGGER.isDebugEnabled()) {
				SESSION_LOGGER.debug(
						"No session found by id: Caching result for getSession(false) for this HttpServletRequest.");
			}
			setAttribute(INVALID_SESSION_ID_ATTR, "true");
		}
	}
	if (!create) {
		return null;
	}
	if (SESSION_LOGGER.isDebugEnabled()) {
		SESSION_LOGGER.debug(
				"A new session was created. To help you troubleshoot where the session was created we provided a StackTrace (this is not an error). You can prevent this from appearing by disabling DEBUG logging for "
						+ SESSION_LOGGER_NAME,
				new RuntimeException(
						"For debugging purposes only (not an error)"));
	}
	// 都没有那么就创建一个新的
	S session = SessionRepositoryFilter.this.sessionRepository.createSession();
	session.setLastAccessedTime(Instant.now());
	currentSession = new HttpSessionWrapper(session, getServletContext());
	setCurrentSession(currentSession);
	return currentSession;
}

private void commitSession() {
	HttpSessionWrapper wrappedSession = getCurrentSession();
	// 如果没有session，并且已经被标记为失效时，调用 onInvalidateSession 进行通知处理
	if (wrappedSession == null) {
		if (isInvalidateClientSession()) {
			SessionRepositoryFilter.this.httpSessionStrategy
					.onInvalidateSession(this, this.response);
		}
	}
	// 如果存在就更新属性值
	else {
		S session = wrappedSession.getSession();
		SessionRepositoryFilter.this.sessionRepository.save(session);
		// 如果请求的sessionId跟当前的session的id不同，或者请求的sessionId无效，
		// 则调用 onNewSession 进行通知处理
		if (!isRequestedSessionIdValid()
				|| !session.getId().equals(getRequestedSessionId())) {
			SessionRepositoryFilter.this.httpSessionStrategy.onNewSession(session,
					this, this.response);
		}
	}
}

public interface SessionRepository<S extends Session> {
	// 创建session
	S createSession();
	
	// 保存session
	void save(S session);
	
	// 根据sessionId 获取
	S findById(String id);

	// 删除特定id的session值
	void deleteById(String id);
}

// 更新失效时间
public void onExpirationUpdated(Long originalExpirationTimeInMilli, Session session) {
	// NO.2 key
	String keyToExpire = "expires:" + session.getId();
	// 往后推迟 lastAccessTime + MaxInactiveInterval
	long toExpire = roundUpToNextMinute(expiresInMillis(session));
	// 原来的NO.3 key 清除掉
	if (originalExpirationTimeInMilli != null) {
		long originalRoundedUp = roundUpToNextMinute(originalExpirationTimeInMilli);
		if (toExpire != originalRoundedUp) {
			String expireKey = getExpirationKey(originalRoundedUp);
			this.redis.boundSetOps(expireKey).remove(keyToExpire);
		}
	}

	long sessionExpireInSeconds = session.getMaxInactiveInterval().getSeconds();
	String sessionKey = getSessionKey(keyToExpire);

	// MaxInactiveInterval < 0 Session永久有效
	if (sessionExpireInSeconds < 0) {
		this.redis.boundValueOps(sessionKey).append("");
		this.redis.boundValueOps(sessionKey).persist();
		this.redis.boundHashOps(getSessionKey(session.getId())).persist();
		return;
	}

	// 拼装NO.3 key
	String expireKey = getExpirationKey(toExpire);
	BoundSetOperations<Object, Object> expireOperations = this.redis
			.boundSetOps(expireKey);
	expireOperations.add(keyToExpire);

	long fiveMinutesAfterExpires = sessionExpireInSeconds
			+ TimeUnit.MINUTES.toSeconds(5);
	// NO.3 key 过期时间是自身时间+5分钟
	expireOperations.expire(fiveMinutesAfterExpires, TimeUnit.SECONDS);
	// sessionKey -> NO.2 key
	if (sessionExpireInSeconds == 0) {
		this.redis.delete(sessionKey);
	}
	else {
		this.redis.boundValueOps(sessionKey).append("");
		this.redis.boundValueOps(sessionKey)
			.expire(sessionExpireInSeconds, TimeUnit.SECONDS);
	}
	// NO.1 也是过期时间推迟5min
	this.redis.boundHashOps(getSessionKey(session.getId()))
			.expire(fiveMinutesAfterExpires, TimeUnit.SECONDS);
}

PUBLISH __keyspace@0__:key expired  
PUBLISH __keyspace@0__:expired key

container.addMessageListener(messageListener,
				Arrays.asList(new PatternTopic("__keyevent@*:del"),
						new PatternTopic("__keyevent@*:expired")));
container.addMessageListener(messageListener, Arrays.asList(new PatternTopic(messageListener.getSessionCreatedChannelPrefix() + "*")));

public void onMessage(Message message, byte[] pattern) {
	byte[] messageChannel = message.getChannel();
	byte[] messageBody = message.getBody();
	if (messageChannel == null || messageBody == null) {
		return;
	}

	String channel = new String(messageChannel);

	// 新建Session
	if (channel.startsWith(getSessionCreatedChannelPrefix())) {
		// TODO: is this thread safe?
		Map<Object, Object> loaded = (Map<Object, Object>) this.defaultSerializer
				.deserialize(message.getBody());
		handleCreated(loaded, channel);
		return;
	}

	String body = new String(messageBody);
	if (!body.startsWith(getExpiredKeyPrefix())) {
		return;
	}

	// 删除及过期Session
	boolean isDeleted = channel.endsWith(":del");
	if (isDeleted || channel.endsWith(":expired")) {
		int beginIndex = body.lastIndexOf(":") + 1;
		int endIndex = body.length();
		String sessionId = body.substring(beginIndex, endIndex);

		RedisSession session = getSession(sessionId, true);

		if (logger.isDebugEnabled()) {
			logger.debug("Publishing SessionDestroyedEvent for session " + sessionId);
		}
		// 清楚登录用户关联的sessionId，如: userId -> set(sessionId)
		cleanupPrincipalIndex(session);

		if (isDeleted) {
			handleDeleted(sessionId, session);
		}
		else {
			handleExpired(sessionId, session);
		}

		return;
	}
}