Java 在jsp和Servlet过滤器中获取相同的会话对象？

我正在为jsp页面中的会话对象设置一个属性，如下所示：

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

然后，我尝试在servlet过滤器中检索该会话属性：

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

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

但是我在这里得到了session对象的null值。在这里获取相同会话对象的正确方法是什么？

该方法可能返回

null

如果create为false并且请求没有有效的HttpSession，则此方法返回null

根据执行

chain.doFilter（请求、响应）的时间，可以在请求资源之前或请求资源之后调用

在您的情况下，您似乎在执行jsp之前查询会话，即执行以下操作：

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

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

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);  
}

改成

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

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

将使其正常工作，但我怀疑您是否打算这样做，因为您可能希望检查远程IP并决定是否允许访问或拒绝访问请求的资源，在这种情况下，您可能希望执行以下操作：

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

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

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);  
}

您确定
request.getRemoteAddr（）
一开始没有给您一个空值吗？