Tomcat Session管理窥探

Manager<<Interface>>管理Session，负责添加value、持久化等。Manager的实现类必须实现Lifecycle接口。

实现类有StandardManager、PersistentManager、BackupManager等。

StandardManager

SessionId和Session的映射是由一个Map管理的。

/**
     * The set of currently active Sessions for this Manager, keyed by
     * session identifier.
     */
    protected Map<String, Session> sessions = new ConcurrentHashMap<>();

Session的持久化是一个名为 SESSIONS.ser 的文件。

/**
     * Path name of the disk file in which active sessions are saved
     * when we stop, and from which these sessions are loaded when we start.
     * A <code>null</code> value indicates that no persistence is desired.
     * If this pathname is relative, it will be resolved against the
     * temporary working directory provided by our context, available via
     * the <code>javax.servlet.context.tempdir</code> context attribute.
     */
    protected String pathname = "SESSIONS.ser";

对Manager正常的使用方法是调用start或stop方法。

start方法

/**
     * Start this component and implement the requirements
     * of {@link org.apache.catalina.util.LifecycleBase#startInternal()}.
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents this component from being used
     */
    @Override
    protected synchronized void startInternal() throws LifecycleException {

        super.startInternal();

        // Load unloaded sessions, if any
        try {
            load();
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            log.error(sm.getString("standardManager.managerLoad"), t);
        }

        setState(LifecycleState.STARTING);
    }

doLoad方法里，使用了ConcurrentHashMap却又对其加了锁。

• 使用CustomObjectInputStream加载持久化Session文件；
• 将session激活；
• 增加session计数。

stop方法

/**
     * Stop this component and implement the requirements
     * of {@link org.apache.catalina.util.LifecycleBase#stopInternal()}.
     *
     * @exception LifecycleException if this component detects a fatal error
     *  that prevents this component from being used
     */
    @Override
    protected synchronized void stopInternal() throws LifecycleException {

        if (log.isDebugEnabled()) {
            log.debug("Stopping");
        }

        setState(LifecycleState.STOPPING);

        // Write out sessions
        try {
            unload();
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            log.error(sm.getString("standardManager.managerUnload"), t);
        }

        // Expire all active sessions
        Session sessions[] = findSessions();
        for (int i = 0; i < sessions.length; i++) {
            Session session = sessions[i];
            try {
                if (session.isValid()) {
                    session.expire();
                }
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
            } finally {
                // Measure against memory leaking if references to the session
                // object are kept in a shared field somewhere
                session.recycle();
            }
        }

        // Require a new random number generator if we are restarted
        super.stopInternal();
    }

调用unload方法，将session过期掉。

在doUnload方法里，使用ObjectOutputStream保存现有sessions，并将sessions过期（重复操作了）。