Detailed Explanation of Writing Filter Selection in jsp

The example is as follows:

public class LoginCheckFilter implements Filter {
private FilterConfig config=null;
private String webroot=null;
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
// TODO Auto-generated method stub
HttpServletRequest request=(HttpServletRequest)req;
HttpServletResponse response=(HttpServletResponse)resp;
HttpSession session=request.getSession(false); //Get the current session's session, do not create a session if there is no session, the same as request.getSession()}
String url = request.getRequestURI(); //Get the current input /Project/Whether the current access path is the same as the path defined by us
if (url != null && url.equals(webroot+"/login.jsp") && url.equals(webroot+"/LoginServlet")){
chain.doFilter(req, resp);
} else {
if (session == null) {
response.sendRedirect(webroot+"/login.jsp
} else {
String user2=(String) session.getAttribute("user1);
if (user2== null) {
response.sendRedirect(webroot+"/login.jsp
} else {
chain.doFilter(request, response);
}
}
}
}
@Override
public void init(FilterConfig config) throws ServletException {
// TODO Auto-generated method stub
this.config = config;
ServletContext ctx = config.getServletContext(); //Get URL  /Project Name
webroot = ctx.getContextPath();    //Project Name
}
}

It should be noted here that the jump used by LoginServlet to jump to the welcome page is a client-side jump.

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