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JAVA´úÂ룺
package com.cq.bean;

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.HttpSession;

/**
* µÇ½¹ýÂËÆ÷
* @author Administrator
*
*/
public class LoginFilter implements Filter{

public void init(FilterConfig arg0) throws ServletException {
}

public void doFilter(ServletRequest request, ServletResponse response,
  FilterChain chain) throws IOException, ServletException {
  
  HttpServletRequest re=(HttpServletRequest)request;
  HttpSession session=re.getSession();
  
  if(session.getAttribute("loginuser")!=null){
  chain.doFilter(request, response);
  }else{
  request.getRequestDispatcher("index.jsp").forward(request, response);
  }
}

public void destroy() {
}
}

web.xmlÅäÖÃÈçÏÂ:
<filter>
  <filter-name>LoginFilter</filter-name>
  <filter-class>com.cq.bean.LoginFilter</filter-class>
</filter>
<filter-mapping>
  <fi