查找从给定客户端IP创建的活动会话数

Question

有没有一种方法可以确定从给定客户端IP地址创建的活动会话数？

Answer 1

标准Servlet API并未为此提供便利。最好你可以做的是保持Map<HttpSession, String>自己（这里String是IP地址），并检查每个ServletRequest如果HttpSession#isNew()并将其添加到Map沿ServletRequest#getRemoteAddr()。然后，您可以使用Collections#frequency()on
获取具有活动会话的IP地址数量Map#values()。你只需要确保您删除HttpSession从Map过程中HttpSessionListener#sessionDestroyed()。

所有这些都可以在一次Listener实现中完成ServletContextListener，HttpSessionListener和ServletRequestListener。

这是一个启动示例：

public class SessionCounter implements ServletContextListener, HttpSessionListener, ServletRequestListener {

    private static final String ATTRIBUTE_NAME = "com.example.SessionCounter";
    private Map<HttpSession, String> sessions = new ConcurrentHashMap<HttpSession, String>();

    @Override
    public void contextInitialized(ServletContextEvent event) {
        event.getServletContext().setAttribute(ATTRIBUTE_NAME, this);
    }

    @Override
    public void requestInitialized(ServletRequestEvent event) {
        HttpServletRequest request = (HttpServletRequest) event.getServletRequest();
        HttpSession session = request.getSession();
        if (session.isNew()) {
            sessions.put(session, request.getRemoteAddr());
        }
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent event) {
        sessions.remove(event.getSession());
    }

    @Override
    public void sessionCreated(HttpSessionEvent event) {
        // NOOP. Useless since we can't obtain IP here.
    }

    @Override
    public void requestDestroyed(ServletRequestEvent event) {
        // NOOP. No logic needed.
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        // NOOP. No logic needed. Maybe some future cleanup?
    }

    public static SessionCounter getInstance(ServletContext context) {
        return (SessionCounter) context.getAttribute(ATTRIBUTE_NAME);
    }

    public int getCount(String remoteAddr) {
        return Collections.frequency(sessions.values(), remoteAddr);
    }

}

定义web.xml如下：

<listener>
    <listener-class>com.example.SessionCounter</listener-class>
</listener>

您可以在任何servlet中使用它，如下所示：

SessionCounter counter = SessionCounter.getInstance(getServletContext());
int count = counter.getCount("127.0.0.1");