过滤器的实现

1.要实现过滤器需要实现过滤接口，并实现过滤器接口的init（）、doFilter（）、destory（）方法。
2.需要在web.xml部署过滤器。
3.具体实现：

public class UrlFilter implements Filter{

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

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		HttpServletRequest req = (HttpServletRequest)request;
		HttpServletResponse rsp = (HttpServletResponse)response;
		String url= req.getRequestURI();
		//拿到url之后就可以根据需要过滤了
		//还可以在web.xml里面配置
		//检查是否合法，根据需要跳转
	}

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

}

<filter>
     <filter-name>URLFilter</filter-name>
     <filter-class>org.filter.URLFilter</filter-class>
   </filter>

  <filter-mapping>
  	<filter-name>URLFilter</filter-name>
  	<url-pattern>/mytest/*</url-pattern>
  </filter-mapping>
  <filter-mapping>
  	<filter-name>URLFilter</filter-name>
  	<url-pattern>/jsp/*</url-pattern>
  </filter-mapping>

4还可以过滤某个特定的servlet

<filter-mapping>
    <filter-name>URLFilter</filter-name>
    <servlet-name>LoginServlet</servlet-name>
</filter-mapping>