2.1.SpringSession源码:getRequestedSession()

private S getRequestedSession() {
	if (!this.requestedSessionCached) {
		List<String> sessionIds = SessionRepositoryFilter.this.httpSessionIdResolver
				.resolveSessionIds(this);
		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;
}

【3】获取sessionId，SpringSession对于sessionId获取的两种策略，一种从Cookie中获取(CookieHttpSessionIdResolver)，也是默认方式.另一种从Header中获取HeaderHttpSessionIdResolver,顺便说下，如果要还一种解析方式，需要预先配置下.

用户代码如下:

 @Configuration
 public class SessionIdResolverConfig {
         @Bean
         public HttpSessionIdResolver httpSessionIdResolver() {
                 return HeaderHttpSessionIdResolver.xAuthToken();
         }
 }

接着说resolveSessionIds,从CookieHttpSessionIdResolver#resolveSessionIds方法进去，内部有个readCookieValues, 直接从request中获取cookies然后循环，找到名称是SESSION，默认进行Base64解码，最后将sessionId放入列表中。

     //DefaultCookieSerializer.java
     @Override
     public List<String> readCookieValues(HttpServletRequest request) {
         Cookie[] cookies = request.getCookies();
         List<String> matchingCookieValues = new ArrayList<>();
         if (cookies != null) {
             for (Cookie cookie : cookies) {
                 if (this.cookieName.equals(cookie.getName())) {
                     String sessionId = (this.useBase64Encoding
                             ? base64Decode(cookie.getValue())
                             : cookie.getValue());
                     if (sessionId == null) {
                         continue;
                     }
                     //TODO:jvmRoute不知道是什么。后期研究下
                     if (this.jvmRoute != null && sessionId.endsWith(this.jvmRoute)) {
                         sessionId = sessionId.substring(0,
                                 sessionId.length() - this.jvmRoute.length());
                     }
                     matchingCookieValues.add(sessionId);
                 }
             }
         }
         return matchingCookieValues;
     }

【5-15】循环从httpSessionIdResolver解析出来的sessionId列表，并且根据sessionId从存储(这里是Redis)中获取Session。顺序是RedisOperationsSessionRepository#findById -> RedisOperationsSessionRepository#getSession

	private RedisSession getSession(String id, boolean allowExpired) {
      Map<Object, Object> entries = getSessionBoundHashOperations(id).entries();
      if (entries.isEmpty()) {
          return null;
      }
      MapSession loaded = loadSession(id, entries);
      if (!allowExpired && loaded.isExpired()) {
          return null;
      }
      RedisSession result = new RedisSession(loaded);
      result.originalLastAccessTime = loaded.getLastAccessedTime();
      return result;
  }

【2】从redis根据sessionId读取信息
【6】本质上就是将读取出来的Map结构转换为自定义的MapSession

【16】获取session成功，顺便就把requestedSessionCached标记下已缓存

2.1.SpringSession源码:getRequestedSession()

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