一个登陆验证的过滤器

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.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class AuthenticationFilter implements Filter {
String url="/";


public void destroy() {
}


public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
ServletException {
HttpServletRequest req =(HttpServletRequest)request;
HttpServletResponse res =(HttpServletResponse)response;
HttpSession session=req.getSession();
if(session.getAttribute("guestbook.admin.username")==null){
res.sendRedirect(req.getContextPath()+url);
return ;
}
chain.doFilter(request, response);
}


public void init(FilterConfig config) throws ServletException {
url=config.getInitParameter("url");

}

}

在web-inf中配置

<filter>
<filter-name>AuthenticationFilter</filter-name>
<filter-class>AuthenticationFilter</filter-class>
<init-param>
<param-name>url</param-name>
<param-value>/admin/login.jsp</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>AuthenticationFilter</filter-name>
<url-pattern>/secure/*</url-pattern>
</filter-mapping>