浅谈Spring Session工作原理

<!-- spring session -->
  <filter>
    <filter-name>springSessionRepositoryFilter</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>springSessionRepositoryFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

<!--创建了一个RedisConnectionFactory，它将Spring会话连接到Redis服务器-->
    <bean id="jedisConnectionFactory" class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory">
        <!--配置Redis连接池 ，可以不配置，使用默认就行！-->
        p:poolConfig-ref="jedisPoolConfig"
    </bean>
 
    <!--创建一个Spring Bean的名称springSessionRepositoryFilter实现过滤器-->
    <bean class="org.springframework.session.data.redis.config.annotation.web.http.RedisHttpSessionConfiguration">
        <!--默认session时效30分钟-->
        <property name="maxInactiveIntervalInSeconds" value="60" />
    </bean>

contextInitialized(ServletContextEvent arg0); // Listener
init(FilterConfig filterConfig); // Filter
init(ServletConfig config); // Servlet

@Bean
public <S extends ExpiringSession> SessionRepositoryFilter<? extends ExpiringSession> springSessionRepositoryFilter(
        SessionRepository<S> sessionRepository) {
    ......
    return sessionRepositoryFilter;
}

public final void init(FilterConfig filterConfig) throws ServletException {
        ......
        // Let subclasses do whatever initialization they like.
        initFilterBean();
        ......
    }

protected void initFilterBean() throws ServletException {
        synchronized (this.delegateMonitor) {
            if (this.delegate == null) {
                // If no target bean name specified, use filter name.
                if (this.targetBeanName == null) {
                    //targetBeanName 为springSessionRepositoryFilter
                    this.targetBeanName = getFilterName();
                }
                WebApplicationContext wac = findWebApplicationContext();
                if (wac != null) {
                    this.delegate = initDelegate(wac);
                }
            }
        }
    }

protected void doFilterInternal(HttpServletRequest request,
           HttpServletResponse response, FilterChain filterChain)
           throws ServletException, IOException {
       request.setAttribute(SESSION_REPOSITORY_ATTR, this.sessionRepository);
       //包装了HttpServletRequest，覆写了HttpServletRequest中 getSession(boolean create)方法
       SessionRepositoryRequestWrapper wrappedRequest = new SessionRepositoryRequestWrapper(
               request, response, this.servletContext);
             ......
       try {
           filterChain.doFilter(strategyRequest, strategyResponse);
       }
       finally {
           //保证session持久化
           wrappedRequest.commitSession();
       }
   }

public void onExpirationUpdated(Long originalExpirationTimeInMilli,
            ExpiringSession session) {
        String keyToExpire = "expires:" + session.getId();
        long toExpire = roundUpToNextMinute(expiresInMillis(session));
                ......
        //把spring:session:sessions:expires加入到spring:session:expirations开头的key里面
        String expireKey = getExpirationKey(toExpire);
        BoundSetOperations<Object, Object> expireOperations = this.redis
                .boundSetOps(expireKey);
        expireOperations.add(keyToExpire);
 
        long fiveMinutesAfterExpires = sessionExpireInSeconds
                + TimeUnit.MINUTES.toSeconds(5);
        //spring:session:expirations开头的key过期时间为xml配置的时间后五分钟
        expireOperations.expire(fiveMinutesAfterExpires, TimeUnit.SECONDS);
        if (sessionExpireInSeconds == 0) {
            this.redis.delete(sessionKey);
        }
        else {
            //spring:session:sessions:expires开头的key过期时间为xml配置的时间
            this.redis.boundValueOps(sessionKey).append("");
            this.redis.boundValueOps(sessionKey).expire(sessionExpireInSeconds,
                    TimeUnit.SECONDS);
        }
        //spring:session:sessions开头的key过期时间为xml配置的时间后五分钟
        this.redis.boundHashOps(getSessionKey(session.getId()))
                .expire(fiveMinutesAfterExpires, TimeUnit.SECONDS);
    }

public void cleanExpiredSessions() {
        long now = System.currentTimeMillis();
        long prevMin = roundDownMinute(now);
        ......
        //获取到spring:session:expirations键
        String expirationKey = getExpirationKey(prevMin);
        // 取出当前这一分钟应当过期的 session
        Set<Object> sessionsToExpire = this.redis.boundSetOps(expirationKey).members();
        // 注意：这里删除的是spring:session:expirations键，不是删除 session 本身！
        this.redis.delete(expirationKey);
        for (Object session : sessionsToExpire) {
            String sessionKey = getSessionKey((String) session);
            //遍历一下spring:session:sessions:expires键
            touch(sessionKey);
        }
    }
 
    /**
     * By trying to access the session we only trigger a deletion if it the TTL is
     * expired. This is done to handle
     * https://github.com/spring-projects/spring-session/issues/93
     *
     * @param key the key
     */
    private void touch(String key) {
        //并不是直接删除 key，而只是访问 key，通过惰性删除确保spring:session:sessions:expires键实时删除，
        // 同时也保证多线程并发续签的场景下，key移动到不同spring:session:expirations键里面时，
        //以spring:session:sessions:expires键实际ttl时间为准
        this.redis.hasKey(key);
    }

public void configure(RedisConnection connection) {
       String notifyOptions = getNotifyOptions(connection);
       String customizedNotifyOptions = notifyOptions;
       if (!customizedNotifyOptions.contains("E")) {
           customizedNotifyOptions += "E";
       }
       boolean A = customizedNotifyOptions.contains("A");
       if (!(A || customizedNotifyOptions.contains("g"))) {
           customizedNotifyOptions += "g";
       }
       if (!(A || customizedNotifyOptions.contains("x"))) {
           customizedNotifyOptions += "x";
       }
       if (!notifyOptions.equals(customizedNotifyOptions)) {
           connection.setConfig(CONFIG_NOTIFY_KEYSPACE_EVENTS, customizedNotifyOptions);
       }
   }

@Bean
 public RedisMessageListenerContainer redisMessageListenerContainer(
         RedisConnectionFactory connectionFactory,
         RedisOperationsSessionRepository messageListener) {
             ......
     //psubscribe del和expired事件
     container.addMessageListener(messageListener,
             Arrays.asList(new PatternTopic("__keyevent@*:del"),
                     new PatternTopic("__keyevent@*:expired")));
     //psubscribe created事件
     container.addMessageListener(messageListener, Arrays.asList(new PatternTopic(
             messageListener.getSessionCreatedChannelPrefix() + "*")));
     return container;
 }

public void onMessage(Message message, byte[] pattern) {
      ......
      if (channel.startsWith(getSessionCreatedChannelPrefix())) {
          ...
          //处理spring:session created事件
          handleCreated(loaded, channel);
          return;
      }
 
      //非spring:session:sessions:expires事件不做处理
      String body = new String(messageBody);
      if (!body.startsWith(getExpiredKeyPrefix())) {
          return;
      }
 
      boolean isDeleted = channel.endsWith(":del");
      if (isDeleted || channel.endsWith(":expired")) {
          ......
          if (isDeleted) {
              //处理spring:session:sessions:expires del事件
              handleDeleted(sessionId, session);
          }
          else {
              //处理spring:session:sessions:expires expired事件
              handleExpired(sessionId, session);
          }
          ......
          return;
      }
  }

@Component
public class SessionExpiredListener implements ApplicationListener<SessionExpiredEvent> {
    @Override
    public void onApplicationEvent(SessionExpiredEvent event) {
        ......
    }
}