src/com/book/filter/LoginFilter.java

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package com.book.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 com.book.pojo.User;

public class LoginFilter implements Filter{

	public void destroy() {
		
	}

	public void doFilter(ServletRequest arg0, ServletResponse arg1,
			FilterChain arg2) throws IOException, ServletException {
		 HttpServletRequest request = (HttpServletRequest)arg0;
		 HttpServletResponse response = (HttpServletResponse) arg1;
		 String url = request.getRequestURI();
		 boolean flag = false;
		 if(url.indexOf(".jsp")==-1){
			 flag = true;
		 }
		 else if(url.indexOf("login") == -1 && url.indexOf("index") == -1 ){
			 User user = (User)request.getSession().getAttribute("user");
			 if(user != null){
				flag = true;
			 }
		 }else{
			 flag = true;
		 }
		 if(flag){
			 arg2.doFilter(arg0, arg1);
		 }else{
			response.sendRedirect(request.getContextPath()+"/index.jsp");
		 }
		
	}

	public void init(FilterConfig arg0) throws ServletException {
		
	}

}