import   java.io.IOException;

import   javax.servlet.Filter;
import   javax.servlet.FilterChain;
import   javax.servlet.FilterConfig;
import   javax.servlet.ServletException;
import   javax.servlet.ServletRequest;
import   javax.servlet.ServletResponse;
import   javax.servlet.http.HttpServletRequest;
import   javax.servlet.http.HttpSession;

public   class   MyFilter   implements   Filter   {

public   void   destroy()   {
//   TODO   Auto-generated   method   stub

}

public   void   doFilter(ServletRequest   req,   ServletResponse   resp,
FilterChain   chain)   throws   IOException,   ServletException   {
HttpServletRequest   request   =   (HttpServletRequest)req;
// String   url   =   request.getContextPath()   +   request.getServletPath();
String   servletPath   =   request.getServletPath();
if(servletPath.equals( "/index.jsp ")   ||   servletPath.equals( "/loginServlet ")){
chain.doFilter(req,   resp);
return;
}

HttpSession   session   =   request.getSession();
User   user   =   (User)session.getAttribute( "user ");
if(user   ==   null){
//非法访问

return;
}   else   {
//合法访问

chain.doFilter(req,   resp);
}

}

public   void   init(FilterConfig   arg0)   throws   ServletException   {
//   TODO   Auto-generated   method   stub

}

}

<servlet>
                <servlet-name> default </servlet-name>
                <servlet-class> org.apache.catalina.servlets.DefaultServlet </servlet-class>
                <init-param>
                        <param-name> debug </param-name>
                        <param-value> 0 </param-value>
                </init-param>
                <init-param>
                        <param-name> listings </param-name>
                        <param-value> true </param-value>
                </init-param>
                <load-on-startup> 1 </load-on-startup>
        </servlet>