Spring Security3源码分析-SessionManagementFilter分析-上

SessionManagementFilter过滤器对应的类路径为
org.springframework.security.web.session.SessionManagementFilter
这个过滤器看名字就知道是管理session的了，http标签是自动配置时，默认是添加SessionManagementFilter过滤器到filterChainProxy中的，如果不想使用这个过滤器，需要做如下配置

<security:http auto-config="true">
  <security:session-management session-fixation-protection="none"/>
</security:http>

其实在之前的过滤器中有使用到session策略了，但是没有细说。
SessionManagementFilter提供两大类功能：
1.session固化保护-通过session-fixation-protection配置
2.session并发控制-通过concurrency-control配置
下面看SessionManagementFilter的bean是如何创建的

    void createSessionManagementFilters() {
        Element sessionMgmtElt = DomUtils.getChildElementByTagName(httpElt, Elements.SESSION_MANAGEMENT);
        Element sessionCtrlElt = null;

        String sessionFixationAttribute = null;
        String invalidSessionUrl = null;
        String sessionAuthStratRef = null;
        String errorUrl = null;
        //如果配置了标签，解析标签的属性、子标签
        if (sessionMgmtElt != null) {
            sessionFixationAttribute = sessionMgmtElt.getAttribute(ATT_SESSION_FIXATION_PROTECTION);
            invalidSessionUrl = sessionMgmtElt.getAttribute(ATT_INVALID_SESSION_URL);
            sessionAuthStratRef = sessionMgmtElt.getAttribute(ATT_SESSION_AUTH_STRATEGY_REF);
            errorUrl = sessionMgmtElt.getAttribute(ATT_SESSION_AUTH_ERROR_URL);
            sessionCtrlElt = DomUtils.getChildElementByTagName(sessionMgmtElt, Elements.CONCURRENT_SESSIONS);
            //判断是否配置了concurrency-control子标签
            if (sessionCtrlElt != null) {
                //配置了并发控制标签则创建并发控制过滤器和session注册的bean定义
                createConcurrencyControlFilterAndSessionRegistry(sessionCtrlElt);
            }
        }

        if (!StringUtils.hasText(sessionFixationAttribute)) {
            sessionFixationAttribute = OPT_SESSION_FIXATION_MIGRATE_SESSION;
        } else if (StringUtils.hasText(sessionAuthStratRef)) {
            pc.getReaderContext().error(ATT_SESSION_FIXATION_PROTECTION + " attribute cannot be used" +
                    " in combination with " + ATT_SESSION_AUTH_STRATEGY_REF, pc.extractSource(sessionCtrlElt));
        }

        boolean sessionFixationProtectionRequired = !sessionFixationAttribute.equals(OPT_SESSION_FIXATION_NO_PROTECTION);

        BeanDefinitionBuilder sessionStrategy;
        //如果配置了concurrency-control子标签
        if (sessionCtrlElt != null) {
            assert sessionRegistryRef != null;
            //session控制策略为ConcurrentSessionControlStrategy
            sessionStrategy = BeanDefinitionBuilder.rootBeanDefinition(ConcurrentSessionControlStrategy.class);
            sessionStrategy.addConstructorArgValue(sessionRegistryRef);

            String maxSessions = sessionCtrlElt.getAttribute("max-sessions");
            //添加最大session数
            if (StringUtils.hasText(maxSessions)) {
                sessionStrategy.addPropertyValue("maximumSessions", maxSessions);
            }
            String exceptionIfMaximumExceeded = sessionCtrlElt.getAttribute("error-if-maximum-exceeded");

            if (StringUtils.hasText(exceptionIfMaximumExceeded)) {
                sessionStrategy.addPropertyValue("exceptionIfMaximumExceeded", exceptionIfMaximumExceeded);
            }
        } else if (sessionFixationProtectionRequired || StringUtils.hasText(invalidSessionUrl)
                || StringUtils.hasText(sessionAuthStratRef)) {
            //如果没有配置concurrency-control子标签
              //session控制策略是SessionFixationProtectionStrategy
            sessionStrategy = BeanDefinitionBuilder.rootBeanDefinition(SessionFixationProtectionStrategy.class);
        } else {
            //<session-management session-fixation-protection="none"/>
            sfpf = null;
            return;
        }
        //创建SessionManagementFilter，并设置依赖的bean、property
        BeanDefinitionBuilder sessionMgmtFilter = BeanDefinitionBuilder.rootBeanDefinition(SessionManagementFilter.class);
        RootBeanDefinition failureHandler = new RootBeanDefinition(SimpleUrlAuthenticationFailureHandler.class);
        if (StringUtils.hasText(errorUrl)) {
            failureHandler.getPropertyValues().addPropertyValue("defaultFailureUrl", errorUrl);
        }
        sessionMgmtFilter.addPropertyValue("authenticationFailureHandler", failureHandler);
        sessionMgmtFilter.addConstructorArgValue(contextRepoRef);

        if (!StringUtils.hasText(sessionAuthStratRef)) {
            BeanDefinition strategyBean = sessionStrategy.getBeanDefinition();

            if (sessionFixationProtectionRequired) {
                sessionStrategy.addPropertyValue("migrateSessionAttributes",
                        Boolean.valueOf(sessionFixationAttribute.equals(OPT_SESSION_FIXATION_MIGRATE_SESSION)));
            }
            sessionAuthStratRef = pc.getReaderContext().generateBeanName(strategyBean);
            pc.registerBeanComponent(new BeanComponentDefinition(strategyBean, sessionAuthStratRef));
        }

        if (StringUtils.hasText(invalidSessionUrl)) {
            sessionMgmtFilter.addPropertyValue("invalidSessionUrl", invalidSessionUrl);
        }

        sessionMgmtFilter.addPropertyReference("sessionAuthenticationStrategy", sessionAuthStratRef);

        sfpf = (RootBeanDefinition) sessionMgmtFilter.getBeanDefinition();
        sessionStrategyRef = new RuntimeBeanReference(sessionAuthStratRef);
    }

    //创建并发控制Filter和session注册的bean
    private void createConcurrencyControlFilterAndSessionRegistry(Element element) {
        final String ATT_EXPIRY_URL = "expired-url";
        final String ATT_SESSION_REGISTRY_ALIAS = "session-registry-alias";
        final String ATT_SESSION_REGISTRY_REF = "session-registry-ref";

        CompositeComponentDefinition compositeDef =
            new CompositeComponentDefinition(element.getTagName(), pc.extractSource(element));
        pc.pushContainingComponent(compositeDef);

        BeanDefinitionRegistry beanRegistry = pc.getRegistry();

        String sessionRegistryId = element.getAttribute(ATT_SESSION_REGISTRY_REF);
        //判断是否配置了session-registry-ref属性，用于扩展
         //默认情况下使用SessionRegistryImpl类管理session的注册
        if (!StringUtils.hasText(sessionRegistryId)) {
            // Register an internal SessionRegistryImpl if no external reference supplied.
            RootBeanDefinition sessionRegistry = new RootBeanDefinition(SessionRegistryImpl.class);
            sessionRegistryId = pc.getReaderContext().registerWithGeneratedName(sessionRegistry);
            pc.registerComponent(new BeanComponentDefinition(sessionRegistry, sessionRegistryId));
        }

        String registryAlias = element.getAttribute(ATT_SESSION_REGISTRY_ALIAS);
        if (StringUtils.hasText(registryAlias)) {
            beanRegistry.registerAlias(sessionRegistryId, registryAlias);
        }
        //创建并发session控制的Filter
        BeanDefinitionBuilder filterBuilder =
                BeanDefinitionBuilder.rootBeanDefinition(ConcurrentSessionFilter.class);
        //注入session的注册实现类
        filterBuilder.addPropertyReference("sessionRegistry", sessionRegistryId);

        Object source = pc.extractSource(element);
        filterBuilder.getRawBeanDefinition().setSource(source);
        filterBuilder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);

        String expiryUrl = element.getAttribute(ATT_EXPIRY_URL);

        if (StringUtils.hasText(expiryUrl)) {
            WebConfigUtils.validateHttpRedirect(expiryUrl, pc, source);
            filterBuilder.addPropertyValue("expiredUrl", expiryUrl);
        }

        pc.popAndRegisterContainingComponent();

        concurrentSessionFilter = filterBuilder.getBeanDefinition();
        sessionRegistryRef = new RuntimeBeanReference(sessionRegistryId);
    }

如果项目需要使用session的并发控制，需要做如下的配置

<session-management invalid-session-url="/login.jsp">
    <concurrency-control max-sessions="1" error-if-maximum-exceeded="true" expired-url="/login.jsp"/>
</session-management>

session-fixation-protection属性支持三种不同的选项允许你使用
none：使得session固化攻击失效（未配置其他属性）
migrateSession：当用户经过认证后分配一个新的session，它保证原session的所有属性移到新session中
newSession：当用户认证后，建立一个新的session，原（未认证时）session的属性不会进行移到新session中来


如果使用了标签concurrency-control，那么filterchainProxy中会添加新的过滤器
ConcurrentSessionFilter。这个过滤器的顺序在SecurityContextPersistenceFilter之前。说明未创建空的认证实体时就需要对session进行并发控制了
看ConcurrentSessionFilter执行过程

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;

        HttpSession session = request.getSession(false);
        if (session != null) {
            //这个SessionInformation是在执行SessionManagementFilter时通过sessionRegistry构造的并且放置在map集合中的
            SessionInformation info = sessionRegistry.getSessionInformation(session.getId());
            //如果当前session已经注册了
            if (info != null) {
                //如果当前session失效了
                if (info.isExpired()) {
                    // Expired - abort processing
                    //强制退出
                    doLogout(request, response);
                    //目标url为expired-url标签配置的属性值
                    String targetUrl = determineExpiredUrl(request, info);
                    //跳转到指定url
                    if (targetUrl != null) {
                        redirectStrategy.sendRedirect(request, response, targetUrl);

                        return;
                    } else {
                        response.getWriter().print("This session has been expired (possibly due to multiple concurrent " +
                                "logins being attempted as the same user).");
                        response.flushBuffer();
                    }

                    return;
                } else {
                    // Non-expired - update last request date/time
                    //session未失效，刷新时间
                    info.refreshLastRequest();
                }
            }
        }

        chain.doFilter(request, response);
    }

那么分析完ConcurrentSessionFilter过滤器的执行过程，具体有什么作用呢？
简单点概括就是：从session缓存中获取当前session信息，如果发现过期了，就跳转到expired-url配置的url或者响应session失效提示信息。当前session有哪些情况会导致session失效呢？这里的失效并不是指在web容器中session的失效，而是spring security把登录成功的session封装为SessionInformation并放到注册类缓存中，如果SessionInformation的expired变量为true，则表示session已失效。
所以，ConcurrentSessionFilter过滤器主要检查SessionInformation的expired变量的值


为了能清楚解释session 并发控制的过程，现在引入UsernamePasswordAuthenticationFilter过滤器，因为该过滤器就是对登录账号进行认证的，并且在分析UsernamePasswordAuthenticationFilter过滤器时，也没有详细讲解session的处理。
UsernamePasswordAuthenticationFilter的doFilter是由父类AbstractAuthenticationProcessingFilter完成的，截取部分重要代码

        try {
            //由子类UsernamePasswordAuthenticationFilter认证
              //之前已经详细分析
            authResult = attemptAuthentication(request, response);
            if (authResult == null) {
                // return immediately as subclass has indicated that it hasn't completed authentication
                return;
            }
            //由session策略类完成session固化处理、并发控制处理
              //如果当前认证实体的已注册session数超出最大并发的session数
              //这里会抛出AuthenticationException
            sessionStrategy.onAuthentication(authResult, request, response);
        }
        catch (AuthenticationException failed) {
            // Authentication failed
            //捕获到异常，直接跳转到失败页面或做其他处理
            unsuccessfulAuthentication(request, response, failed);

            return;
        }

session处理的方法就是这一语句

sessionStrategy.onAuthentication(authResult, request, response);

如果是采用了并发控制session，则sessionStrategy为ConcurrentSessionControlStrategy类，具体源码：

    public void onAuthentication(Authentication authentication, HttpServletRequest request,
            HttpServletResponse response) {
        //检查是否允许认证
        checkAuthenticationAllowed(authentication, request);

        // Allow the parent to create a new session if necessary
        //执行父类SessionFixationProtectionStrategy的onAuthentication，完成session固化工作。其实就是重新建立一个session，并且把之前的session失效掉。
        super.onAuthentication(authentication, request, response);
        //向session注册类SessionRegistryImpl注册当前session、认证实体
         //实际上SessionRegistryImpl维护两个缓存列表，分别是
         //1.sessionIds（Map）：key=sessionid，value=SessionInformation
        //2.principals（Map）：key=principal，value=HashSet
        sessionRegistry.registerNewSession(request.getSession().getId(), authentication.getPrincipal());
    }
    //检查是否允许认证通过，如果通过直接返回，不通过，抛出AuthenticationException
    private void checkAuthenticationAllowed(Authentication authentication, HttpServletRequest request)
            throws AuthenticationException {
        //获取当前认证实体的session集合
        final List<SessionInformation> sessions = sessionRegistry.getAllSessions(authentication.getPrincipal(), false);

        int sessionCount = sessions.size();
        //获取的并发session数（由max-sessions属性配置）
        int allowedSessions = getMaximumSessionsForThisUser(authentication);
        //如果当前认证实体的已注册session数小于max-sessions，允许通过
        if (sessionCount < allowedSessions) {
            // They haven't got too many login sessions running at present
            return;
        }
        //如果allowedSessions配置为-1，说明未限制并发session数，允许通过
        if (allowedSessions == -1) {
            // We permit unlimited logins
            return;
        }
        //如果当前认证实体的已注册session数等于max-sessions
        //判断当前的session是否已经注册过了，如果注册过了，允许通过
        if (sessionCount == allowedSessions) {
            HttpSession session = request.getSession(false);

            if (session != null) {
                // Only permit it though if this request is associated with one of the already registered sessions
                for (SessionInformation si : sessions) {
                    if (si.getSessionId().equals(session.getId())) {
                        return;
                    }
                }
            }
            // If the session is null, a new one will be created by the parent class, exceeding the allowed number
        }
        //以上条件都不满足时，进一步处理
        allowableSessionsExceeded(sessions, allowedSessions, sessionRegistry);
    }

    protected void allowableSessionsExceeded(List<SessionInformation> sessions, int allowableSessions,
            SessionRegistry registry) throws SessionAuthenticationException {
        //判断配置的error-if-maximum-exceeded属性，如果为true，抛出异常
        if (exceptionIfMaximumExceeded || (sessions == null)) {
            throw new SessionAuthenticationException(messages.getMessage("ConcurrentSessionControllerImpl.exceededAllowed",
                    new Object[] {new Integer(allowableSessions)},
                    "Maximum sessions of {0} for this principal exceeded"));
        }
        //如果配置的error-if-maximum-exceeded为false，接下来就是取出最先注册的session信息（这里是封装到SessionInformation），然后让最先认证成功的session过期。当ConcurrentSessionFilter过滤器检查到这个过期的session，就执行session失效的处理。
        // Determine least recently used session, and mark it for invalidation
        SessionInformation leastRecentlyUsed = null;

        for (int i = 0; i < sessions.size(); i++) {
            if ((leastRecentlyUsed == null)
                    || sessions.get(i).getLastRequest().before(leastRecentlyUsed.getLastRequest())) {
                leastRecentlyUsed = sessions.get(i);
            }
        }
        leastRecentlyUsed.expireNow();
    }

经过以上分析，可以这么理解

如果concurrency-control标签配置了error-if-maximum-exceeded="true"，max-sessions="1"，那么第二次登录时，是登录不了的。如果error-if-maximum-exceeded="false"，那么第二次是能够登录到系统的，但是第一个登录的账号再次发起请求时，会跳转到expired-url配置的url中（如果没有配置，则显示This session has been expired (possibly due to multiple concurrent logins being attempted as the same user).提示信息）

由于篇幅过长，SessionManagementFilter、org.springframework.security.web.session.HttpSessionEventPublisher就放到下部分再分析了