Java使用Filter实现登录验证

public class LoginFilter implements Filter{
	//销毁方法
	public void destroy() {
	}
	public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
			throws IOException, ServletException {
		//将ServletRequest转化成HttpServletRequest
	  HttpServletRequest request=(HttpServletRequest)servletRequest;
        HttpServletResponse response=(HttpServletResponse)servletResponse;
        //获取当前用户的请求地址
        String url=request.getRequestURI();
        //如果请求的地址中包含login,就放行
        //如果用户正在通过login.jsp或者请求login.do进行登录，要放行。
        if(url.indexOf("login")>-1){
        	//放行
        	filterChain.doFilter(request, response);
        	return ;
        }
        HttpSession session=request.getSession();
        String username=(String)session.getAttribute("username");
        //如果username值为空，说明没有登录，因为登录成功后会将用户信息保存在session中。
        if(username!=null){
        	//放行
        	filterChain.doFilter(request, response);
        	return ;
        }
        //如果没有登录转发到login.jsp
        request.getRequestDispatcher("login.jsp").forward(request, response);
	}
	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
		
	}

}

<!-- 自定义过滤器 -->
  <filter>
        <filter-name> LoginFilter </filter-name>
        <filter-class>com.it.filter. LoginFilter </filter-class>
    </filter>
    <filter-mapping>
        <filter-name> LoginFilter </filter-name>
        <url-pattern>/*</url-pattern>
</filter-mapping>