servlet+jsp实现过滤器 防止用户未登录访问（servlet入门教程）太疯狂了

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginFilter implements Filter {
public static final String login_page=”/test/admin/index.jsp”;
public static final String logout_page=”/test/admin/Public/login.jsp”;
public void destroy(){

}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)throws ServletException, IOException {
HttpServletRequest request=(HttpServletRequest)servletRequest;
HttpServletResponse response=(HttpServletResponse)servletResponse;
String currentURL=request.getRequestURI();
String ctxPath=request.getContextPath();
//除掉项目名称时访问页面当前路径
String targetURL=currentURL.substring(ctxPath.length());
HttpSession session=request.getSession(false);
//对当前页面进行判断，如果当前页面不为登录页面
if(!(“/admin/Public/login.jsp”.equals(targetURL))){
System.out.println(“1″+targetURL+”ctxPath:”+ctxPath+”currentURL:”+currentURL);
//在不为登陆页面时，再进行判断，如果不是登陆页面也没有session则跳转到登录页面，
if(session==null || session.getAttribute(“admin”)==null){
response.sendRedirect(logout_page);
return;
}else{
//这里表示正确，会去寻找下一个链，如果不存在，则进行正常的页面跳转
filterChain.doFilter(request, response);
return;
}
}else{
//这里表示如果当前页面是登陆页面，跳转到登陆页面
filterChain.doFilter(request, response);
return;
}

}
public void init(FilterConfig filterConfig)throws ServletException{

}

}