Cannot create a session after the response has been committed

		ServletOutputStream os = resp.getOutputStream();
		String serverCode = CheckCodeUtil.outputVerifyImage(100, 50, os, 5);

        HttpSession session = req.getSession();
        session.setAttribute("serverCode", serverCode);

不知道为什么 response响应处理之后，再次获取session会报错，先记录下来

了解到的信息为，获取session的时机，当获取session的时机在 response处理之后会抛出此异常，将获取session的代码提取到response之前即可

java.lang.IllegalStateException: Cannot create a session after the response has been committed
	at org.apache.catalina.connector.Request.doGetSession(Request.java:2921)
	at org.apache.catalina.connector.Request.getSession(Request.java:2318)
	```