MSM源代码分析

memcached session manager（MSM） 用集中式缓存方式解决了集群环境的session共享
MSM用MemcachedBackupSessionManager类替换了StandardManager

1 MSM通过两个Valve拦截Request请求实现了对Session的操作

RequestTrackingHostValve
RequestTrackingContextValve

这两个Valve是在startInternal()方法中加载的 如下代码

        _trackingHostValve = new RequestTrackingHostValve(_requestUriIgnorePattern, sessionCookieName, this, _statistics, _enabled, _currentRequest);
        _manager.getContainer().getParent().getPipeline().addValve(_trackingHostValve);
        _trackingContextValve = new RequestTrackingContextValve(sessionCookieName, this);
        _manager.getContainer().getPipeline().addValve( _trackingContextValve );

先看RequestTrackingHostValve做了什么？

    @Override
    public void invoke( final Request request, final Response response ) throws IOException, ServletException {

        final String requestId = getURIWithQueryString( request );
        if(!_enabled.get() || !_msmContext.equals(request.getContext())) {
            getNext().invoke( request, response );
        } else if ( _ignorePattern != null && _ignorePattern.matcher( requestId ).matches() ) {
            if(_log.isDebugEnabled()) {
                _log.debug( ">>>>>> Ignoring: " + requestId + " (requestedSessionId "+ request.getRequestedSessionId() +") ==================" );
            }

            try {
                storeRequestThreadLocal( request );
                request.setNote(REQUEST_IGNORED, Boolean.TRUE);
                getNext().invoke( request, response );
            } finally {
                if(request.getNote(REQUEST_PROCESSED) == Boolean.TRUE) {
                    final String sessionId = getSessionId(request, response);
                    if(sessionId != null) {
                        _sessionBackupService.requestFinished(sessionId, requestId);
                    }
                }
                resetRequestThreadLocal();
            }
            if(_log.isDebugEnabled()) {
                _log.debug( "<<<<<< Ignored: " + requestId + " ==================" );
            }
        } else {

            request.setNote(REQUEST_PROCESS, Boolean.TRUE);

            if ( _log.isDebugEnabled() ) {
                _log.debug( ">>>>>> Request starting: " + requestId + " (requestedSessionId "+ request.getRequestedSessionId() +") ==================" );
            }
//请求开始，注意这里并没有从memcached获取session，而是在用户调用request.getSession()才从memcached获取
            try {
                storeRequestThreadLocal( request ); //保存request到ThreadLocal
                getNext().invoke( request, response ); //调用下一个Valve
            } finally {
                final Boolean sessionIdChanged = (Boolean) request.getNote(SESSION_ID_CHANGED);
//在请求结束时保存session到memcached
                backupSession( request, response, sessionIdChanged == null ? false : sessionIdChanged.booleanValue() );
                resetRequestThreadLocal();
            }

            if ( _log.isDebugEnabled() ) {
                logDebugRequestSessionCookie( request );
                logDebugResponseCookie( response );
                _log.debug( "<<<<<< Request finished: " + requestId + " ==================" );
            }

        }
    }