filter过滤器的应用

filter过滤器的使用
  在jsp开发中，我们经常使用过滤器（filter）来过滤权限，我做了一个简单的过滤器，代码如下：
（1）web.xml中加入：
<filter>
  <filter-name>adminfilter</filter-name>
  <filter-class>org.frank.filter.AdminFilter</filter-class>
  <init-param>
   <param-name>jspDirectAccess</param-name>
   <param-value>login,/img/</param-value>
  </init-param>
  <init-param>
   <param-name>forwardPage</param-name>
   <param-value>/login.do</param-value>
  </init-param>
</filter>

  <filter-mapping>
  <filter-name>adminfilter</filter-name>
  <url-pattern>/*</url-pattern>
  <dispatcher>REQUEST</dispatcher>
       </filter-mapping>
注意：jspDirectAccess，是定义不登录的时候允许访问的地址，比如登录页面、登录页面用到的图片等等，多个地址使用逗号分开。
      forwardPage是定义跳转的页面。
      <filter-mapping> 一般是声明在其他过滤器的前面，避免引起过滤器失效等其他异常。

（2）定义过滤器AdminFilter类：

package org.frank.filter;

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;

import org.seasar.struts.util.RequestUtil;

public class AdminFilter implements Filter {

private String access = "login";
private String forward = "/login";
private static final String[] SESSIONS = {"userInfoSessionDto"};

@Override
public void destroy() {

}

@Override
public void doFilter(ServletRequest arg0, ServletResponse arg1,
   FilterChain arg2) throws IOException, ServletException {
  HttpServletRequest req = (HttpServletRequest)arg0;
  HttpServletResponse res = (HttpServletResponse) arg1;  
  HttpSession session = req.getSession(true);  
  String path = RequestUtil.getPath(req);
   if(processDirectAccess(path)){
    arg2.doFilter(arg0, arg1);  
   }else{
    if(session==null || session.getAttribute(SESSIONS[0])==null || "".equals(session.getAttribute(SESSIONS[0]))){
           req.getRequestDispatcher(forward).forward(arg0, arg1);
           res.setHeader("Cache-Control","no-store");     
               res.setDateHeader("Expires",1000);  
               res.setHeader("Pragma","no-cache");  
               return;
          }else{
           arg2.doFilter(arg0, arg1);  
          }
   }
           
       
}

public boolean processDirectAccess(String path){
  if(path==null && "".equals(path)){
   return false;
  }
  if(access!=null){
   String[] accs = access.split(",");
   for(String acc:accs){
    if(path.lastIndexOf(acc + ".do") >=0 || path.lastIndexOf(acc) >=0){
     return true;
    }
   }
  }
  return false;
}

@Override
public void init(FilterConfig arg0) throws ServletException {
  this.access = arg0.getInitParameter("jspDirectAccess");
  this.forward = arg0.getInitParameter("forwardPage");
}

}

（3）登录成功保存session
session.setAttribute("userInfoSessionDto", userInfoSessionDto);
注意：
  session中存入的userInfoSessionDto要和AdminFilter类中的SESSIONS[0]的值对应。