通过api：Shiro的Session接口有一个setTimeout()方法
//登录后，可以用如下方式取得session SecurityUtils.getSubject().getSession().setTimeout(30000);
查看Shiro的api文档，
setTimeout
void setTimeout(long maxIdleTimeInMillis) throws InvalidSessionExceptionSets the time in milliseconds that the session may remain idle before expiring.A negative value means the session will never expire.A non-negative value (0 or greater) means the session
expiration will occur if idle for that length of time.*Note: if you are used to the HttpSession's getMaxInactiveInterval() method, the scale on this method is different: Shiro Sessions use millisecond values for timeout whereas HttpSession.getMaxInactiveInterval
uses seconds. Always use millisecond values with Shiro sessions.Parameters:maxIdleTimeInMillis - the time in milliseconds that the session may remain idle before expiring.Throws:InvalidSessionException - if the session has been stopped or expired prior to
calling this method.Since:0.2
设置的最大时间，正负都可以，为负数时表示永不超时。开发过程中，设置负数时，遇到点儿问题：
SecurityUtils.getSubject().getSession().setTimeout(-1l);
这样调用后，总是抛出session已经过时的异常，一直找不到原因，后来调试源码才发现，这里设置的时间单位是:ms，但是Shiro会把这个时间转成:s，而且是会舍掉小数部分，这样我设置的是-1ms，转成s后就是0s，马上就过期了，所以后面再对这个会话进行操作时，总会抛异常，正确的设置永不超时的方式应该是：
// timeout:-1000ms 永不超时
SecurityUtils.getSubject().getSession().setTimeout(-1000l);