BaseServlet的抽取与优化(减少创建多个Servlet类)，利用反射机制进行抽取

package com.feilong.shop.controller;

import com.feilong.shop.utils.Constants;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Method;

/**
 * @author FeiLong
 * @version 1.8
 * @date 2020/9/13 17:47
 */
@SuppressWarnings("ALL")
public class BaseServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        //获取请求的uri地址的标识
        String uri = req.getRequestURI();
        //通过截取得到标识对应的方法名称
        String methodName = uri.substring(uri.lastIndexOf("/") + 1);
        if (methodName == null && methodName.equals("")) {
            methodName = Constants.INDEX;//methodName为空时赋值为index然后调用index方法跳转到index界面
        }
        //利用反射机制拿到对应的方法
        try {
            Method method = this.getClass().getMethod(methodName, HttpServletRequest.class, HttpServletResponse.class);
            //执行方法
            Object result = method.invoke(this, req, resp);
            //集中处理响应结果
            if (result != null) {
                String str = (String) result;
                if (str.startsWith(Constants.FORWARD)) {//forward
                    //转发
                    String path = str.substring(str.indexOf(Constants.FLAG) + 1);//:
                    req.getRequestDispatcher(path).forward(req, resp);
                } else if (str.startsWith(Constants.REDIRECT)) {//redirect
                    //重定向
                    String path = str.substring(str.indexOf(Constants.FLAG) + 1);
                    resp.sendRedirect(path);
                } else {
                    resp.getWriter().println(str);
                }
            }
        } catch (Exception e) {
            //没有找到反射方法
            e.printStackTrace();
            req.getSession().setAttribute("msg", "程序异常请稍后再试...");
            resp.sendRedirect("/message.jsp");
        }
    }

    /**
     * 当method标识符‘没有值’ 我们默认赋 index 访问每个controller的index方法！
     * 我们将方法提取到baseservlet中即可！
     * 默认处理：跳转到程序的首页！
     *
     * @param req
     * @param resp
     * @return
     * @throws IOException
     * @throws ServletException
     */
    public String index(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {

        return Constants.REDIRECT + "/index.jsp";
    }
}

编写完后根据模块进行编写Servlet，一个用户模块对应一个Servlet，里面的方法对应要进行的操作，模块的Servlet都要继承这个BaseServlet，不要再继承HttpServlet了！
再进行配置注解的时候最好这样配置 /user/*
当访问用户模块服务器时确保要访问到里面的每一个对应的方法
示例 用户模块

package com.feilong.shop.controller;

import com.feilong.shop.entity.User;
import com.feilong.shop.service.UserService;
import com.feilong.shop.service.impl.UserServiceImpl;
import com.feilong.shop.utils.Base64Utils;
import com.feilong.shop.utils.Constants;
import com.feilong.shop.utils.MD5Utils;
import com.feilong.shop.utils.RandomUtils;
import org.apache.commons.beanutils.BeanUtils;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.Map;

/**
 * @author FeiLong
 * @version 1.8
 * @date 2020/9/13 18:06
 */
@SuppressWarnings("ALL")
@WebServlet("/user/*")
public class UserServletController extends BaseServlet {
    private UserService userService = new UserServiceImpl();

    /**
     * 检测用户名是否存在的方法
     *
     * @param req
     * @param resp
     * @return 1 存在 不可注册  0不存在可注册
     * @throws Exception
     */
    public String check(HttpServletRequest req, HttpServletResponse resp) throws Exception {
        String username = req.getParameter("username");
        if (username == null) {
            return Constants.USERHAS;//用户名为空不可注册
        }

        boolean checked = userService.checked(username);
        if (checked) {
            return Constants.USERHAS;//用户名存在不可注册
        } else {
            return Constants.USERNOHAS;
        }
    }

    /**
     * 用户注册的方法
     *
     * @param req
     * @param resp
     * @return 注册成功跳转到成功界面  失败跳转到注册界面
     */
    public String register(HttpServletRequest req, HttpServletResponse resp) {
        Map<String, String[]> map = req.getParameterMap();
        User user = new User();
        try {
            BeanUtils.populate(user, map);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(user);
        //完善用户信息
        //已经赋值：用户姓名  用户密码 邮箱  性别
        //未赋值：激活状态 激活码  账号类型
        user.setUstatus(Constants.USER_NOT_ACTIVE);//0代表未激活  1代表激活
        user.setCode(RandomUtils.createActive());//随机生成激活码
        user.setUrole(Constants.USER_CUSTOMER);//普通客户0   管理员1
        //密码进行MD5加密
        user.setUpassword(MD5Utils.md5(user.getUpassword()));

        int result = userService.registerUser(user);
        if (result > 0) {
            return Constants.REDIRECT + "/registerSuccess.jsp";
        } else {
            req.getSession().setAttribute("registerMsg", "注册失败！");
            return Constants.FORWARD + "/register.jsp";
        }
    }

    /**
     * 邮箱激活
     * @param req
     * @param resp
     * @return
     */
    public String active(HttpServletRequest req, HttpServletResponse resp) {
        //1.得到的结果是base64编码
        String code = req.getParameter("c");
        //2.进行base64解码
        String decode = Base64Utils.decode(code);
        int status = userService.activeUser(decode);
        if (status == Constants.ACTIVE_FAIL) {
            req.setAttribute("msg", "激活失败！");
        } else if (status == Constants.ACTIVE_SUCCESS) {
            req.setAttribute("msg", "激活成功！请返回登录！");
        } else {
            req.setAttribute("msg", "已经激活，请勿重复操作！");
        }
        return Constants.FORWARD + "/message.jsp";

    }

    /**
     * 用户登录
     * @param req
     * @param resp
     * @return
     */
    public String login(HttpServletRequest req, HttpServletResponse resp) {
        //获取参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String code = req.getParameter("code");//用户输入的验证码
        String auto = req.getParameter("auto");
        //获取存储的验证码
        String code_session = (String) req.getSession().getAttribute("code");//正确的验证码
        if (code == null || !code.equalsIgnoreCase(code_session)) {
            req.setAttribute("msg", "验证码输入有误！");
            return Constants.FORWARD + "/login.jsp";
        }


        /* 调用业务逻辑方法
           loginUser为空证明用户名或密码错误
           loginUser不为空  但是user处于未激活状态
         */
        User loginUser = userService.login(username, password);
        if (loginUser == null) {
            //用户为空转发登录页
            req.setAttribute("msg", "用户名或密码错误！");
            return Constants.FORWARD + "/login.jsp";
        }

        if (loginUser.getUstatus() != Constants.USERACTIVE) {
            //未激活转发到登录页
            req.setAttribute("msg", "账号未激活！");
            return Constants.FORWARD + "/login.jsp";
        }
        req.getSession().setAttribute("loginUser", loginUser);

        if (auto == null) {
            //没有勾选自动登录
            //将本地浏览器的Cookie清空
            Cookie cookie = new Cookie(Constants.COOKIE_USER, "");
            cookie.setPath("/");
            cookie.setMaxAge(0);//立即删除
            resp.addCookie(cookie);
        } else {
            //不为空代表已经勾选
            //需要将用户名和密码存储到浏览器
            String content = username + Constants.FLAG + password;
            //将内容进行base64编码存储  安全性高
            String encodeContent = Base64Utils.encode(content);
            System.out.println(encodeContent);
            Cookie cookie = new Cookie(Constants.COOKIE_USER, encodeContent);
            cookie.setPath("/");
            cookie.setMaxAge(60 * 60 * 24 * 14);//两周
            resp.addCookie(cookie);
        }

        //用户不为空并且已经激活，可以跳转详情页
        return Constants.FORWARD + "/index.jsp";
    }

    /**
     * 用户注销
     * @param req
     * @param resp
     * @return
     */
    public String logout(HttpServletRequest req, HttpServletResponse resp) {
        //1.清除session中的数据
        HttpSession session = req.getSession();
        session.removeAttribute("loginUser");
        //2.清除Cookie
        Cookie cookie = new Cookie(Constants.COOKIE_USER, "");
        cookie.setPath("/");
        cookie.setMaxAge(0);
        resp.addCookie(cookie);

        req.setAttribute("msg", "账户注销成功！");
        return Constants.FORWARD + "/login.jsp";

    }
}