在登录时生成Session
```java
if ("admin".equals(username) && "123".equals(password)) {
	req.getSession().setAttribute(JavaBean.USER_SESSION, req.getSession().getId());
	resp.sendRedirect("/status/success.html");
} else {
	resp.sendRedirect("/error.html");
}
```
然后注销，清空Session的值
```java
Object user_session = req.getSession().getAttribute(JavaBean.USER_SESSION);
if (user_session != null) {
	req.getSession().removeAttribute(JavaBean.USER_SESSION);
	resp.sendRedirect("/login.html");
} else {
	resp.sendRedirect("/login.html");
}
```
然后过滤器
```java
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;

if (request.getSession().getAttribute(JavaBean.USER_SESSION) == null) {
	response.sendRedirect("/error.html");
}

chain.doFilter(request, response);
```
![](https://kuangstudy.oss-cn-beijing.aliyuncs.com/bbs/2021/04/18/kuangstudy43613a45-3935-41c0-9420-998dac75e05f.png)
![](https://kuangstudy.oss-cn-beijing.aliyuncs.com/bbs/2021/04/18/kuangstudy3c445bf5-a28b-4402-ab75-fbaf135dd366.jpg)
![](https://kuangstudy.oss-cn-beijing.aliyuncs.com/bbs/2021/04/18/kuangstudyb2730697-a01b-4063-bf7d-6088db01ad6f.png)
![](https://kuangstudy.oss-cn-beijing.aliyuncs.com/bbs/2021/04/18/kuangstudy80ae9fa6-0174-4c65-b18c-bf6bf21bcb87.png)
![](https://kuangstudy.oss-cn-beijing.aliyuncs.com/bbs/2021/04/18/kuangstudydad17d8d-382e-453b-b8ac-a409ec25c5d4.png)

Servlet中登录生成session后注销，第一次用地址访问Filter不起作用，第二次才起作用，是为什么？

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