package com.javaweb.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;

public abstract class HttpFilter implements Filter {

    private FilterConfig filterConfig;

    @Override

    public void destroy() {

    }

    @Override

    public void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)

            throws IOException, ServletException {

        HttpServletRequest request=(HttpServletRequest)servletrequest;

        HttpServletResponse response=(HttpServletResponse)servletresponse;

        doFilter(request,response,filterchain);

    }

    public abstract void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterchain)

            throws IOException, ServletException ;

    @Override

    public void init(FilterConfig filterconfig) throws ServletException {

        this.filterConfig=filterconfig;

        init();

    }

    public FilterConfig getFilterConfig() {

        return filterConfig;

    }

    public void init() throws ServletException{

    }

}

package com.javaweb.login;

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;

public class LoginFilter extends HttpFilter {

    public void destroy() {
        // TODO Auto-generated method stub
        System.out.println("离开LoginFilter");
    }

    public void init() throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("初始化LoginFilter 只会出现一次！");
    }

    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterchain)
            throws IOException, ServletException {
        System.out.println("进入LoginFilter");
        filterchain.doFilter(request, response);//放行
        System.out.println("离开LoginFilter");
    }
}

package com.javaweb.listener;

import javax.servlet.ServletRequestAttributeEvent;

import javax.servlet.ServletRequestAttributeListener;

import javax.servlet.ServletRequestEvent;

import javax.servlet.ServletRequestListener;

public class MyHttpRequestListener implements ServletRequestListener,ServletRequestAttributeListener {

    @Override

    public void requestDestroyed(ServletRequestEvent servletrequestevent) {

        System.out.println("requestDestroyed...");

    }

    @Override

    public void requestInitialized(ServletRequestEvent servletrequestevent) {

        System.out.println("requestInitialized...");

    }

    @Override

    public void attributeAdded(ServletRequestAttributeEvent servletrequestattributeevent) {

        // TODO Auto-generated method stub

    }

    @Override

    public void attributeRemoved(ServletRequestAttributeEvent servletrequestattributeevent) {

        // TODO Auto-generated method stub

    }

    @Override

    public void attributeReplaced(ServletRequestAttributeEvent servletrequestattributeevent) {

        // TODO Auto-generated method stub

    }

}

package com.javaweb.login;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

public class LoginServlet extends HttpServlet {

    private static final long serialVersionUID = -6820554522964310475L;

    private String userName;

    private String password;

    public void init(){

        userName=getServletConfig().getInitParameter("username");

        password=getServletConfig().getInitParameter("password");

    }

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        doPost(req, resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String username=req.getParameter("username");

        String pwd=req.getParameter("password");

        if(username!=null && !"".equals(username) && pwd!=null && !"".equals(pwd)){

            if(userName.equals(username) && password.equals(pwd)){

                HttpSession session=req.getSession();

                session.setAttribute("username", username);

                session.setAttribute("password", pwd);

                resp.sendRedirect(req.getContextPath()+"/login.jsp");

            }else{

                resp.sendRedirect(req.getContextPath()+"/index.jsp");

            }

        }

    }

}