SpringSession：请求与响应重写

private final class SessionRepositoryRequestWrapper
            extends HttpServletRequestWrapper {
    // HttpServletResponse 实例
    private final HttpServletResponse response;
    // ServletContext 实例
    private final ServletContext servletContext;
        // requestedSession session对象
        private S requestedSession; 
        // 是否缓存 session
        private boolean requestedSessionCached;
    // sessionId
    private String requestedSessionId;
    // sessionId 是否有效
    private Boolean requestedSessionIdValid;
    // sessionId 是否失效
    private boolean requestedSessionInvalidated;

    // 省略方法
}

private SessionRepositoryRequestWrapper(HttpServletRequest request,
        HttpServletResponse response, ServletContext servletContext) {
    super(request);
    this.response = response;
    this.servletContext = servletContext;
}

@Override
public HttpSessionWrapper getSession(boolean create) {
    // 从当前请求线程中获取 session
    HttpSessionWrapper currentSession = getCurrentSession();
    // 如果有直接返回
    if (currentSession != null) {
        return currentSession;
    }
    // 从请求中获取 session，这里面会涉及到从缓存中拿session的过程
    S requestedSession = getRequestedSession();
    if (requestedSession != null) {
        // 无效的会话id(不支持的会话存储库)请求属性名称。
        // 这里看下当前的sessionId是否有效
        if (getAttribute(INVALID_SESSION_ID_ATTR) == null) {
            // 设置当前session的最后访问时间，用于延迟session的有效期
            requestedSession.setLastAccessedTime(Instant.now());
            // 将requestedSessionIdValid置为true
            this.requestedSessionIdValid = true;
            // 包装session
            currentSession = new HttpSessionWrapper(requestedSession, getServletContext());
            // 不是新的session，如果是新的session则需要改变sessionId
            currentSession.setNew(false);
            // 将session设置到当前请求上下文
            setCurrentSession(currentSession);
            // 返回session
            return currentSession;
        }
    }
    else {
        // 这里处理的是无效的sessionId的情况，但是当前请求线程 session有效
        if (SESSION_LOGGER.isDebugEnabled()) {
            SESSION_LOGGER.debug(
                    "No session found by id: Caching result for getSession(false) for this HttpServletRequest.");
        }
        // 将invalidSessionId置为true
        setAttribute(INVALID_SESSION_ID_ATTR, "true");
    }
    // 是否需要创建新的session
    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)"));
    }
    // 创建新的session
    S session = SessionRepositoryFilter.this.sessionRepository.createSession();
    // 设置最后访问时间，也就是指定了当前session的有效期限
    session.setLastAccessedTime(Instant.now());
    // 包装下当前session
    currentSession = new HttpSessionWrapper(session, getServletContext());
    //设置到当前请求线程
    setCurrentSession(currentSession);
    return currentSession;
}

private S getRequestedSession() {
    // 缓存的请求session是否存在
    if (!this.requestedSessionCached) {
            // 获取 sessionId
            List<String> sessionIds = SessionRepositoryFilter.this.httpSessionIdResolver
                    .resolveSessionIds(this);
            // 通过sessionId来从存储中获取session
            for (String sessionId : sessionIds) {
                if (this.requestedSessionId == null) {
                    this.requestedSessionId = sessionId;
                }
                S session = SessionRepositoryFilter.this.sessionRepository
                        .findById(sessionId);
                if (session != null) {
                    this.requestedSession = session;
                    this.requestedSessionId = sessionId;
                    break;
                }
            }
            this.requestedSessionCached = true;
    }
    return this.requestedSession;
}

@Override
public Object getAttribute(String name) {
    checkState();
    return this.session.getAttribute(name);
}