jsp 过滤器（filter) 中session, application(servletContext)的获取

import java.io.IOException;

import javax.jms.Session;
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.SessionTrackingMode;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EncodingFilter implements Filter{
	public void init(FilterConfig config)throws ServletException{
		System.out.println("初始化");
	}
IOException,ServletException{
	public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain) throws IOException, ServletException{
		
		request.setCharacterEncoding("utf-8");
		
		HttpServletRequest req=(HttpServletRequest)request; //强制转换
                HttpServletResponse resp=(HttpServletResponse)response; 
		HttpSession session = req.getSession();
                ServletContext application = req.getServletContext();
        if(session.getAttribute("session") == null){
    	    session.setAttribute("session", "session");
        }
        
		chain.doFilter(request, response);
	}
	public void destroy() {
		System.out.println("destroy");
	}
}