在jsp和Servlet Filter中获取相同的会话对象？

Question

我设置在JSP页面中的会话对象的属性，如下图所示：

String remoteAddr = request.getRemoteAddr(); 
session.setAttribute("remoteAddr",remoteAddr); 

于是，我试图找回在Servlet过滤器会话属性：

public void doFilter(ServletRequest request, ServletResponse response, 
         FilterChain chain) throws IOException, ServletException { 

HttpServletRequest httpServletRequest = (HttpServletRequest) request; 
String remoteIP = httpServletRequest.getSession(false).getAttribute("remoteAddr"); 
} 

但我在这里获得会话对象的空值。在这里获得同样的会话对象的正确方法是什么？

Answer 1

方法HttpServletRequest.html#getSession(boolean)可能返回null

如果制作的是虚假的，该请求没有有效的HttpSession，此方法返回null。被请求的资源之前

一个Filter可调用或取决于当您执行chain.doFilter(request, response);

你的情况，它要求后，似乎是你查询会话执行之前的JSP，即做什么像这样：

HttpServletRequest httpServletRequest = (HttpServletRequest) request; 
String remoteIP = (String) httpServletRequest.getSession(false).getAttribute("remoteAddr"); 

// pass the request along the filter chain 
chain.doFilter(request, response); 

将其更改为

// pass the request along the filter chain 
chain.doFilter(request, response); 

HttpServletRequest httpServletRequest = (HttpServletRequest) request; 
String remoteIP = (String) httpServletRequest.getSession(false).getAttribute("remoteAddr"); 

它会工作，但我怀疑这是你打算做的，因为你可能想检查远程IP并决定是否允许访问或拒绝它请求的资源，在这种情况下，你可能想要做一些事情像这样：

String remoteIP= request.getRemoteAddr(); 

if(remoteIP.matches("some pattern")) { 
    ((HttpServletResponse)response).setStatus(HttpServletResponse.SC_FORBIDDEN); 
} else { 
    // pass the request along the filter chain 
    chain.doFilter(request, response); 
}