java使用过滤器实现 请求转发

///------java 代码

package  com.msw.tools;

import java.io.IOException;
import java.util.Properties;

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;

public class   UserFilter    implements Filter
{

    public void destroy()
    {
    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain filterChain) throws IOException, ServletException
    {
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse res = (HttpServletResponse)response;
        Properties pro=new Properties();
        pro.load(getClass().getResourceAsStream("/url.properties"));//如果是直接copy地址栏参数，则不让登录系统
        String login_url = pro.getProperty("login_url");
        if( null == req.getSession().getAttribute("admin"))//当前登录系统的用户
        {
            res.sendRedirect(login_url);
        }
        else
            filterChain.doFilter(req, res);
    }

    public void init(FilterConfig arg0) throws ServletException
    {
    }

}//

//2/-----如果使用此过滤器 需要在配置文件中加入如下代码.. web.xml

   <filter>
        <filter-name>userFilter</filter-name>
        <filter-class>com.msw.tools.UserFilter</filter-class>
    </filter>

<filter-mapping>
        <filter-name>userFilter</filter-name>
        <url-pattern>/admin/*</url-pattern> // 过滤范围：对后台管理员模块过滤
</filter-mapping>