Filter实现自动登录

filter的简介

filter是对客户端访问资源的过滤，符合条件放行，不符合条件不放行，并且可以对目 标资源访问前后进行逻辑处理

步骤：

思路： 前台有一个 <input type="checkbox" name="autoLogin" value="autoLogin"> 自动登录，当判断选中的时候，把username和password存到cookie中，当你关闭浏览器，再次打开的时候，先经过filter，判断cookie中是否有username和password，如果有，取出来，从数据库中查到user，存到session中，chain.doFilter(request, response);放行，就达到自动登陆的目的。

1. 编写一个过滤器的类实现Filter接口
2. 实现接口中尚未实现的方法(着重实现doFilter方法)
3. 在web.xml中进行配置(主要是配置要对哪些资源进行过滤)

 前台是一个form表单login.jsp

success.jsp  成功就可以取出session中的user

            <c:if test="${empty user }">
				<li><a href="login.jsp">登录</a></li>
				<li><a href="register.jsp">注册</a></li>
			</c:if>
			<c:if test="${!empty user }">
				<li>欢迎您,${user.username }</li>
				<li><a href="#">退出</a></li>
			</c:if>

1. 编写servlet

        request.setCharacterEncoding("UTF-8");
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		HttpSession session = request.getSession();
		
		loginService loginService = new loginService();
		User user = null;
		try {
                //从数据库中根据username和password查询user
			user = loginService.findUser(username,password);
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		if(user!=null) {
			String autoLogin = request.getParameter("autoLogin");
			if(autoLogin!=null) {
                    //对username进行编码（如果是中文）
				String username_code = URLEncoder.encode(username, "UTF-8");
                    //username和password  cookie
				Cookie cookie_username = new Cookie("username1",username_code);
				Cookie cookie_password = new Cookie("password1",user.getPassword());
                    //设置存活时间
				cookie_username.setMaxAge(60*60);
				cookie_password.setMaxAge(60*60);
                    //设置访问路径
				cookie_username.setPath(request.getContextPath());
				cookie_password.setPath(request.getContextPath());
				response.addCookie(cookie_username);
				response.addCookie(cookie_password);
			}
                //存在session中
			session.setAttribute("user", user);
			response.sendRedirect(request.getContextPath());
		}else {
			System.out.println(username);
			request.setAttribute("loginInfo", "用户名或密码错误");
			request.getRequestDispatcher("/login.jsp").forward(request, response);
		}

2.过滤器的类实现Filter接口

package web.filter;

import java.io.IOException;
import java.sql.SQLException;

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

import com.ithiema.domain.User;
import com.ithiema.service.loginService;

public class AutoLogin implements Filter{

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
			throws IOException, ServletException {
		
		String cookie_username = null;
		String cookie_password = null;
		
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) res;
		HttpSession session = request.getSession();
		Cookie[] cookies = request.getCookies();
		if(cookies!=null) {
			for(Cookie cookie:cookies) {
				if("username1".equals(cookie.getName())) {
					cookie_username = cookie.getValue();
				}
				if("password1".equals(cookie.getName())) {
					cookie_password = cookie.getValue();
				}
			}
		}
		if(cookie_username!=null&&cookie_password!=null) {
			loginService loginService = new loginService();
			User user = null;
			try {
                            //取出username和password  从数据库中查user
				user = loginService.findUser(cookie_username, cookie_password);
			} catch (SQLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			session.setAttribute("user", user);
		}
                //放行
		chain.doFilter(request, response);
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
		
	}

}

3.web.xml中添加这个

  <filter>
    <filter-name>AutoLoginFilter</filter-name>
    <filter-class>web.filter.AutoLogin</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>AutoLoginFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>